TOMOYO Linux Cross Reference
Linux/fs/namespace.c

   /*
    *  linux/fs/namespace.c
    *
    * (C) Copyright Al Viro 2000, 2001
    *      Released under GPL v2.
    *
    * Based on code from fs/super.c, copyright Linus Torvalds and others.
    * Heavily rewritten.
    */
  
  #include <linux/syscalls.h>
  #include <linux/export.h>
  #include <linux/capability.h>
  #include <linux/mnt_namespace.h>
  #include <linux/user_namespace.h>
  #include <linux/namei.h>
  #include <linux/security.h>
  #include <linux/idr.h>
  #include <linux/init.h>         /* init_rootfs */
  #include <linux/fs_struct.h>    /* get_fs_root et.al. */
  #include <linux/fsnotify.h>     /* fsnotify_vfsmount_delete */
  #include <linux/uaccess.h>
  #include <linux/proc_ns.h>
  #include <linux/magic.h>
  #include <linux/bootmem.h>
  #include <linux/task_work.h>
  #include "pnode.h"
  #include "internal.h"
  
  static unsigned int m_hash_mask __read_mostly;
  static unsigned int m_hash_shift __read_mostly;
  static unsigned int mp_hash_mask __read_mostly;
  static unsigned int mp_hash_shift __read_mostly;
  
  static __initdata unsigned long mhash_entries;
  static int __init set_mhash_entries(char *str)
  {
          if (!str)
                  return 0;
          mhash_entries = simple_strtoul(str, &str, 0);
          return 1;
  }
  __setup("mhash_entries=", set_mhash_entries);
  
  static __initdata unsigned long mphash_entries;
  static int __init set_mphash_entries(char *str)
  {
          if (!str)
                  return 0;
          mphash_entries = simple_strtoul(str, &str, 0);
          return 1;
  }
  __setup("mphash_entries=", set_mphash_entries);
  
  static u64 event;
  static DEFINE_IDA(mnt_id_ida);
  static DEFINE_IDA(mnt_group_ida);
  static DEFINE_SPINLOCK(mnt_id_lock);
  static int mnt_id_start = 0;
  static int mnt_group_start = 1;
  
  static struct hlist_head *mount_hashtable __read_mostly;
  static struct hlist_head *mountpoint_hashtable __read_mostly;
  static struct kmem_cache *mnt_cache __read_mostly;
  static DECLARE_RWSEM(namespace_sem);
  
  /* /sys/fs */
  struct kobject *fs_kobj;
  EXPORT_SYMBOL_GPL(fs_kobj);
  
  /*
   * vfsmount lock may be taken for read to prevent changes to the
   * vfsmount hash, ie. during mountpoint lookups or walking back
   * up the tree.
   *
   * It should be taken for write in all cases where the vfsmount
   * tree or hash is modified or when a vfsmount structure is modified.
   */
  __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
  
  static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
  {
          unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
          tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
          tmp = tmp + (tmp >> m_hash_shift);
          return &mount_hashtable[tmp & m_hash_mask];
  }
  
  static inline struct hlist_head *mp_hash(struct dentry *dentry)
  {
          unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
          tmp = tmp + (tmp >> mp_hash_shift);
          return &mountpoint_hashtable[tmp & mp_hash_mask];
  }
  
  /*
   * allocation is serialized by namespace_sem, but we need the spinlock to
   * serialize with freeing.
   */
 static int mnt_alloc_id(struct mount *mnt)
 {
         int res;
 
 retry:
         ida_pre_get(&mnt_id_ida, GFP_KERNEL);
         spin_lock(&mnt_id_lock);
         res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
         if (!res)
                 mnt_id_start = mnt->mnt_id + 1;
         spin_unlock(&mnt_id_lock);
         if (res == -EAGAIN)
                 goto retry;
 
         return res;
 }
 
 static void mnt_free_id(struct mount *mnt)
 {
         int id = mnt->mnt_id;
         spin_lock(&mnt_id_lock);
         ida_remove(&mnt_id_ida, id);
         if (mnt_id_start > id)
                 mnt_id_start = id;
         spin_unlock(&mnt_id_lock);
 }
 
 /*
  * Allocate a new peer group ID
  *
  * mnt_group_ida is protected by namespace_sem
  */
 static int mnt_alloc_group_id(struct mount *mnt)
 {
         int res;
 
         if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
                 return -ENOMEM;
 
         res = ida_get_new_above(&mnt_group_ida,
                                 mnt_group_start,
                                 &mnt->mnt_group_id);
         if (!res)
                 mnt_group_start = mnt->mnt_group_id + 1;
 
         return res;
 }
 
 /*
  * Release a peer group ID
  */
 void mnt_release_group_id(struct mount *mnt)
 {
         int id = mnt->mnt_group_id;
         ida_remove(&mnt_group_ida, id);
         if (mnt_group_start > id)
                 mnt_group_start = id;
         mnt->mnt_group_id = 0;
 }
 
 /*
  * vfsmount lock must be held for read
  */
 static inline void mnt_add_count(struct mount *mnt, int n)
 {
 #ifdef CONFIG_SMP
         this_cpu_add(mnt->mnt_pcp->mnt_count, n);
 #else
         preempt_disable();
         mnt->mnt_count += n;
         preempt_enable();
 #endif
 }
 
 /*
  * vfsmount lock must be held for write
  */
 unsigned int mnt_get_count(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         unsigned int count = 0;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
         }
 
         return count;
 #else
         return mnt->mnt_count;
 #endif
 }
 
 static void drop_mountpoint(struct fs_pin *p)
 {
         struct mount *m = container_of(p, struct mount, mnt_umount);
         dput(m->mnt_ex_mountpoint);
         pin_remove(p);
         mntput(&m->mnt);
 }
 
 static struct mount *alloc_vfsmnt(const char *name)
 {
         struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
         if (mnt) {
                 int err;
 
                 err = mnt_alloc_id(mnt);
                 if (err)
                         goto out_free_cache;
 
                 if (name) {
                         mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
                         if (!mnt->mnt_devname)
                                 goto out_free_id;
                 }
 
 #ifdef CONFIG_SMP
                 mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
                 if (!mnt->mnt_pcp)
                         goto out_free_devname;
 
                 this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
 #else
                 mnt->mnt_count = 1;
                 mnt->mnt_writers = 0;
 #endif
 
                 INIT_HLIST_NODE(&mnt->mnt_hash);
                 INIT_LIST_HEAD(&mnt->mnt_child);
                 INIT_LIST_HEAD(&mnt->mnt_mounts);
                 INIT_LIST_HEAD(&mnt->mnt_list);
                 INIT_LIST_HEAD(&mnt->mnt_expire);
                 INIT_LIST_HEAD(&mnt->mnt_share);
                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
                 INIT_LIST_HEAD(&mnt->mnt_slave);
                 INIT_HLIST_NODE(&mnt->mnt_mp_list);
 #ifdef CONFIG_FSNOTIFY
                 INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
 #endif
                 init_fs_pin(&mnt->mnt_umount, drop_mountpoint);
         }
         return mnt;
 
 #ifdef CONFIG_SMP
 out_free_devname:
         kfree_const(mnt->mnt_devname);
 #endif
 out_free_id:
         mnt_free_id(mnt);
 out_free_cache:
         kmem_cache_free(mnt_cache, mnt);
         return NULL;
 }
 
 /*
  * Most r/o checks on a fs are for operations that take
  * discrete amounts of time, like a write() or unlink().
  * We must keep track of when those operations start
  * (for permission checks) and when they end, so that
  * we can determine when writes are able to occur to
  * a filesystem.
  */
 /*
  * __mnt_is_readonly: check whether a mount is read-only
  * @mnt: the mount to check for its write status
  *
  * This shouldn't be used directly ouside of the VFS.
  * It does not guarantee that the filesystem will stay
  * r/w, just that it is right *now*.  This can not and
  * should not be used in place of IS_RDONLY(inode).
  * mnt_want/drop_write() will _keep_ the filesystem
  * r/w.
  */
 int __mnt_is_readonly(struct vfsmount *mnt)
 {
         if (mnt->mnt_flags & MNT_READONLY)
                 return 1;
         if (mnt->mnt_sb->s_flags & MS_RDONLY)
                 return 1;
         return 0;
 }
 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 
 static inline void mnt_inc_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         this_cpu_inc(mnt->mnt_pcp->mnt_writers);
 #else
         mnt->mnt_writers++;
 #endif
 }
 
 static inline void mnt_dec_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         this_cpu_dec(mnt->mnt_pcp->mnt_writers);
 #else
         mnt->mnt_writers--;
 #endif
 }
 
 static unsigned int mnt_get_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         unsigned int count = 0;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
         }
 
         return count;
 #else
         return mnt->mnt_writers;
 #endif
 }
 
 static int mnt_is_readonly(struct vfsmount *mnt)
 {
         if (mnt->mnt_sb->s_readonly_remount)
                 return 1;
         /* Order wrt setting s_flags/s_readonly_remount in do_remount() */
         smp_rmb();
         return __mnt_is_readonly(mnt);
 }
 
 /*
  * Most r/o & frozen checks on a fs are for operations that take discrete
  * amounts of time, like a write() or unlink().  We must keep track of when
  * those operations start (for permission checks) and when they end, so that we
  * can determine when writes are able to occur to a filesystem.
  */
 /**
  * __mnt_want_write - get write access to a mount without freeze protection
  * @m: the mount on which to take a write
  *
  * This tells the low-level filesystem that a write is about to be performed to
  * it, and makes sure that writes are allowed (mnt it read-write) before
  * returning success. This operation does not protect against filesystem being
  * frozen. When the write operation is finished, __mnt_drop_write() must be
  * called. This is effectively a refcount.
  */
 int __mnt_want_write(struct vfsmount *m)
 {
         struct mount *mnt = real_mount(m);
         int ret = 0;
 
         preempt_disable();
         mnt_inc_writers(mnt);
         /*
          * The store to mnt_inc_writers must be visible before we pass
          * MNT_WRITE_HOLD loop below, so that the slowpath can see our
          * incremented count after it has set MNT_WRITE_HOLD.
          */
         smp_mb();
         while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
                 cpu_relax();
         /*
          * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
          * be set to match its requirements. So we must not load that until
          * MNT_WRITE_HOLD is cleared.
          */
         smp_rmb();
         if (mnt_is_readonly(m)) {
                 mnt_dec_writers(mnt);
                 ret = -EROFS;
         }
         preempt_enable();
 
         return ret;
 }
 
 /**
  * mnt_want_write - get write access to a mount
  * @m: the mount on which to take a write
  *
  * This tells the low-level filesystem that a write is about to be performed to
  * it, and makes sure that writes are allowed (mount is read-write, filesystem
  * is not frozen) before returning success.  When the write operation is
  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
  */
 int mnt_want_write(struct vfsmount *m)
 {
         int ret;
 
         sb_start_write(m->mnt_sb);
         ret = __mnt_want_write(m);
         if (ret)
                 sb_end_write(m->mnt_sb);
         return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write);
 
 /**
  * mnt_clone_write - get write access to a mount
  * @mnt: the mount on which to take a write
  *
  * This is effectively like mnt_want_write, except
  * it must only be used to take an extra write reference
  * on a mountpoint that we already know has a write reference
  * on it. This allows some optimisation.
  *
  * After finished, mnt_drop_write must be called as usual to
  * drop the reference.
  */
 int mnt_clone_write(struct vfsmount *mnt)
 {
         /* superblock may be r/o */
         if (__mnt_is_readonly(mnt))
                 return -EROFS;
         preempt_disable();
         mnt_inc_writers(real_mount(mnt));
         preempt_enable();
         return 0;
 }
 EXPORT_SYMBOL_GPL(mnt_clone_write);
 
 /**
  * __mnt_want_write_file - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
  * This is like __mnt_want_write, but it takes a file and can
  * do some optimisations if the file is open for write already
  */
 int __mnt_want_write_file(struct file *file)
 {
         if (!(file->f_mode & FMODE_WRITER))
                 return __mnt_want_write(file->f_path.mnt);
         else
                 return mnt_clone_write(file->f_path.mnt);
 }
 
 /**
  * mnt_want_write_file - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
  * This is like mnt_want_write, but it takes a file and can
  * do some optimisations if the file is open for write already
  */
 int mnt_want_write_file(struct file *file)
 {
         int ret;
 
         sb_start_write(file->f_path.mnt->mnt_sb);
         ret = __mnt_want_write_file(file);
         if (ret)
                 sb_end_write(file->f_path.mnt->mnt_sb);
         return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write_file);
 
 /**
  * __mnt_drop_write - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *
  * Tells the low-level filesystem that we are done
  * performing writes to it.  Must be matched with
  * __mnt_want_write() call above.
  */
 void __mnt_drop_write(struct vfsmount *mnt)
 {
         preempt_disable();
         mnt_dec_writers(real_mount(mnt));
         preempt_enable();
 }
 
 /**
  * mnt_drop_write - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *
  * Tells the low-level filesystem that we are done performing writes to it and
  * also allows filesystem to be frozen again.  Must be matched with
  * mnt_want_write() call above.
  */
 void mnt_drop_write(struct vfsmount *mnt)
 {
         __mnt_drop_write(mnt);
         sb_end_write(mnt->mnt_sb);
 }
 EXPORT_SYMBOL_GPL(mnt_drop_write);
 
 void __mnt_drop_write_file(struct file *file)
 {
         __mnt_drop_write(file->f_path.mnt);
 }
 
 void mnt_drop_write_file(struct file *file)
 {
         mnt_drop_write(file->f_path.mnt);
 }
 EXPORT_SYMBOL(mnt_drop_write_file);
 
 static int mnt_make_readonly(struct mount *mnt)
 {
         int ret = 0;
 
         lock_mount_hash();
         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
         /*
          * After storing MNT_WRITE_HOLD, we'll read the counters. This store
          * should be visible before we do.
          */
         smp_mb();
 
         /*
          * With writers on hold, if this value is zero, then there are
          * definitely no active writers (although held writers may subsequently
          * increment the count, they'll have to wait, and decrement it after
          * seeing MNT_READONLY).
          *
          * It is OK to have counter incremented on one CPU and decremented on
          * another: the sum will add up correctly. The danger would be when we
          * sum up each counter, if we read a counter before it is incremented,
          * but then read another CPU's count which it has been subsequently
          * decremented from -- we would see more decrements than we should.
          * MNT_WRITE_HOLD protects against this scenario, because
          * mnt_want_write first increments count, then smp_mb, then spins on
          * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
          * we're counting up here.
          */
         if (mnt_get_writers(mnt) > 0)
                 ret = -EBUSY;
         else
                 mnt->mnt.mnt_flags |= MNT_READONLY;
         /*
          * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
          * that become unheld will see MNT_READONLY.
          */
         smp_wmb();
         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
         unlock_mount_hash();
         return ret;
 }
 
 static void __mnt_unmake_readonly(struct mount *mnt)
 {
         lock_mount_hash();
         mnt->mnt.mnt_flags &= ~MNT_READONLY;
         unlock_mount_hash();
 }
 
 int sb_prepare_remount_readonly(struct super_block *sb)
 {
         struct mount *mnt;
         int err = 0;
 
         /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
         if (atomic_long_read(&sb->s_remove_count))
                 return -EBUSY;
 
         lock_mount_hash();
         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
                 if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
                         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
                         smp_mb();
                         if (mnt_get_writers(mnt) > 0) {
                                 err = -EBUSY;
                                 break;
                         }
                 }
         }
         if (!err && atomic_long_read(&sb->s_remove_count))
                 err = -EBUSY;
 
         if (!err) {
                 sb->s_readonly_remount = 1;
                 smp_wmb();
         }
         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
                 if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
                         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
         }
         unlock_mount_hash();
 
         return err;
 }
 
 static void free_vfsmnt(struct mount *mnt)
 {
         kfree_const(mnt->mnt_devname);
 #ifdef CONFIG_SMP
         free_percpu(mnt->mnt_pcp);
 #endif
         kmem_cache_free(mnt_cache, mnt);
 }
 
 static void delayed_free_vfsmnt(struct rcu_head *head)
 {
         free_vfsmnt(container_of(head, struct mount, mnt_rcu));
 }
 
 /* call under rcu_read_lock */
 bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 {
         struct mount *mnt;
         if (read_seqretry(&mount_lock, seq))
                 return false;
         if (bastard == NULL)
                 return true;
         mnt = real_mount(bastard);
         mnt_add_count(mnt, 1);
         if (likely(!read_seqretry(&mount_lock, seq)))
                 return true;
         if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
                 mnt_add_count(mnt, -1);
                 return false;
         }
         rcu_read_unlock();
         mntput(bastard);
         rcu_read_lock();
         return false;
 }
 
 /*
  * find the first mount at @dentry on vfsmount @mnt.
  * call under rcu_read_lock()
  */
 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
 {
         struct hlist_head *head = m_hash(mnt, dentry);
         struct mount *p;
 
         hlist_for_each_entry_rcu(p, head, mnt_hash)
                 if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
                         return p;
         return NULL;
 }
 
 /*
  * find the last mount at @dentry on vfsmount @mnt.
  * mount_lock must be held.
  */
 struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
 {
         struct mount *p, *res = NULL;
         p = __lookup_mnt(mnt, dentry);
         if (!p)
                 goto out;
         if (!(p->mnt.mnt_flags & MNT_UMOUNT))
                 res = p;
         hlist_for_each_entry_continue(p, mnt_hash) {
                 if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
                         break;
                 if (!(p->mnt.mnt_flags & MNT_UMOUNT))
                         res = p;
         }
 out:
         return res;
 }
 
 /*
  * lookup_mnt - Return the first child mount mounted at path
  *
  * "First" means first mounted chronologically.  If you create the
  * following mounts:
  *
  * mount /dev/sda1 /mnt
  * mount /dev/sda2 /mnt
  * mount /dev/sda3 /mnt
  *
  * Then lookup_mnt() on the base /mnt dentry in the root mount will
  * return successively the root dentry and vfsmount of /dev/sda1, then
  * /dev/sda2, then /dev/sda3, then NULL.
  *
  * lookup_mnt takes a reference to the found vfsmount.
  */
 struct vfsmount *lookup_mnt(struct path *path)
 {
         struct mount *child_mnt;
         struct vfsmount *m;
         unsigned seq;
 
         rcu_read_lock();
         do {
                 seq = read_seqbegin(&mount_lock);
                 child_mnt = __lookup_mnt(path->mnt, path->dentry);
                 m = child_mnt ? &child_mnt->mnt : NULL;
         } while (!legitimize_mnt(m, seq));
         rcu_read_unlock();
         return m;
 }
 
 /*
  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
  *                         current mount namespace.
  *
  * The common case is dentries are not mountpoints at all and that
  * test is handled inline.  For the slow case when we are actually
  * dealing with a mountpoint of some kind, walk through all of the
  * mounts in the current mount namespace and test to see if the dentry
  * is a mountpoint.
  *
  * The mount_hashtable is not usable in the context because we
  * need to identify all mounts that may be in the current mount
  * namespace not just a mount that happens to have some specified
  * parent mount.
  */
 bool __is_local_mountpoint(struct dentry *dentry)
 {
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         struct mount *mnt;
         bool is_covered = false;
 
         if (!d_mountpoint(dentry))
                 goto out;
 
         down_read(&namespace_sem);
         list_for_each_entry(mnt, &ns->list, mnt_list) {
                 is_covered = (mnt->mnt_mountpoint == dentry);
                 if (is_covered)
                         break;
         }
         up_read(&namespace_sem);
 out:
         return is_covered;
 }
 
 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
 {
         struct hlist_head *chain = mp_hash(dentry);
         struct mountpoint *mp;
 
         hlist_for_each_entry(mp, chain, m_hash) {
                 if (mp->m_dentry == dentry) {
                         /* might be worth a WARN_ON() */
                         if (d_unlinked(dentry))
                                 return ERR_PTR(-ENOENT);
                         mp->m_count++;
                         return mp;
                 }
         }
         return NULL;
 }
 
 static struct mountpoint *new_mountpoint(struct dentry *dentry)
 {
         struct hlist_head *chain = mp_hash(dentry);
         struct mountpoint *mp;
         int ret;
 
         mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
         if (!mp)
                 return ERR_PTR(-ENOMEM);
 
         ret = d_set_mounted(dentry);
         if (ret) {
                 kfree(mp);
                 return ERR_PTR(ret);
         }
 
         mp->m_dentry = dentry;
         mp->m_count = 1;
         hlist_add_head(&mp->m_hash, chain);
         INIT_HLIST_HEAD(&mp->m_list);
         return mp;
 }
 
 static void put_mountpoint(struct mountpoint *mp)
 {
         if (!--mp->m_count) {
                 struct dentry *dentry = mp->m_dentry;
                 BUG_ON(!hlist_empty(&mp->m_list));
                 spin_lock(&dentry->d_lock);
                 dentry->d_flags &= ~DCACHE_MOUNTED;
                 spin_unlock(&dentry->d_lock);
                 hlist_del(&mp->m_hash);
                 kfree(mp);
         }
 }
 
 static inline int check_mnt(struct mount *mnt)
 {
         return mnt->mnt_ns == current->nsproxy->mnt_ns;
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void touch_mnt_namespace(struct mnt_namespace *ns)
 {
         if (ns) {
                 ns->event = ++event;
                 wake_up_interruptible(&ns->poll);
         }
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void __touch_mnt_namespace(struct mnt_namespace *ns)
 {
         if (ns && ns->event != event) {
                 ns->event = event;
                 wake_up_interruptible(&ns->poll);
         }
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void unhash_mnt(struct mount *mnt)
 {
         mnt->mnt_parent = mnt;
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         list_del_init(&mnt->mnt_child);
         hlist_del_init_rcu(&mnt->mnt_hash);
         hlist_del_init(&mnt->mnt_mp_list);
         put_mountpoint(mnt->mnt_mp);
         mnt->mnt_mp = NULL;
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void detach_mnt(struct mount *mnt, struct path *old_path)
 {
         old_path->dentry = mnt->mnt_mountpoint;
         old_path->mnt = &mnt->mnt_parent->mnt;
         unhash_mnt(mnt);
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void umount_mnt(struct mount *mnt)
 {
         /* old mountpoint will be dropped when we can do that */
         mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
         unhash_mnt(mnt);
 }
 
 /*
  * vfsmount lock must be held for write
  */
 void mnt_set_mountpoint(struct mount *mnt,
                         struct mountpoint *mp,
                         struct mount *child_mnt)
 {
         mp->m_count++;
         mnt_add_count(mnt, 1);  /* essentially, that's mntget */
         child_mnt->mnt_mountpoint = dget(mp->m_dentry);
         child_mnt->mnt_parent = mnt;
         child_mnt->mnt_mp = mp;
         hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void attach_mnt(struct mount *mnt,
                         struct mount *parent,
                         struct mountpoint *mp)
 {
         mnt_set_mountpoint(parent, mp, mnt);
         hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 }
 
 static void attach_shadowed(struct mount *mnt,
                         struct mount *parent,
                         struct mount *shadows)
 {
         if (shadows) {
                 hlist_add_behind_rcu(&mnt->mnt_hash, &shadows->mnt_hash);
                 list_add(&mnt->mnt_child, &shadows->mnt_child);
         } else {
                 hlist_add_head_rcu(&mnt->mnt_hash,
                                 m_hash(&parent->mnt, mnt->mnt_mountpoint));
                 list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
         }
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void commit_tree(struct mount *mnt, struct mount *shadows)
 {
         struct mount *parent = mnt->mnt_parent;
         struct mount *m;
         LIST_HEAD(head);
         struct mnt_namespace *n = parent->mnt_ns;
 
         BUG_ON(parent == mnt);
 
         list_add_tail(&head, &mnt->mnt_list);
         list_for_each_entry(m, &head, mnt_list)
                 m->mnt_ns = n;
 
         list_splice(&head, n->list.prev);
 
         attach_shadowed(mnt, parent, shadows);
         touch_mnt_namespace(n);
 }
 
 static struct mount *next_mnt(struct mount *p, struct mount *root)
 {
         struct list_head *next = p->mnt_mounts.next;
         if (next == &p->mnt_mounts) {
                 while (1) {
                         if (p == root)
                                 return NULL;
                         next = p->mnt_child.next;
                         if (next != &p->mnt_parent->mnt_mounts)
                                 break;
                         p = p->mnt_parent;
                 }
         }
         return list_entry(next, struct mount, mnt_child);
 }
 
 static struct mount *skip_mnt_tree(struct mount *p)
 {
         struct list_head *prev = p->mnt_mounts.prev;
         while (prev != &p->mnt_mounts) {
                 p = list_entry(prev, struct mount, mnt_child);
                 prev = p->mnt_mounts.prev;
         }
         return p;
 }
 
 struct vfsmount *
 vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
 {
         struct mount *mnt;
         struct dentry *root;
 
         if (!type)
                 return ERR_PTR(-ENODEV);
 
         mnt = alloc_vfsmnt(name);
         if (!mnt)
                 return ERR_PTR(-ENOMEM);
 
         if (flags & MS_KERNMOUNT)
                 mnt->mnt.mnt_flags = MNT_INTERNAL;
 
         root = mount_fs(type, flags, name, data);
         if (IS_ERR(root)) {
                 mnt_free_id(mnt);
                 free_vfsmnt(mnt);
                 return ERR_CAST(root);
         }
 
         mnt->mnt.mnt_root = root;
         mnt->mnt.mnt_sb = root->d_sb;
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         mnt->mnt_parent = mnt;
         lock_mount_hash();
         list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
         unlock_mount_hash();
         return &mnt->mnt;
 }
 EXPORT_SYMBOL_GPL(vfs_kern_mount);
 
 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
                                         int flag)
 {
         struct super_block *sb = old->mnt.mnt_sb;
         struct mount *mnt;
         int err;
 
         mnt = alloc_vfsmnt(old->mnt_devname);
         if (!mnt)
                 return ERR_PTR(-ENOMEM);
 
         if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
                 mnt->mnt_group_id = 0; /* not a peer of original */
         else
                 mnt->mnt_group_id = old->mnt_group_id;
 
         if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
                 err = mnt_alloc_group_id(mnt);
                 if (err)
                         goto out_free;
         }
 
         mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~(MNT_WRITE_HOLD|MNT_MARKED);
         /* Don't allow unprivileged users to change mount flags */
         if (flag & CL_UNPRIVILEGED) {
                 mnt->mnt.mnt_flags |= MNT_LOCK_ATIME;
 
                 if (mnt->mnt.mnt_flags & MNT_READONLY)
                         mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
 
                 if (mnt->mnt.mnt_flags & MNT_NODEV)
                         mnt->mnt.mnt_flags |= MNT_LOCK_NODEV;
 
                 if (mnt->mnt.mnt_flags & MNT_NOSUID)
                         mnt->mnt.mnt_flags |= MNT_LOCK_NOSUID;
 
                 if (mnt->mnt.mnt_flags & MNT_NOEXEC)
                         mnt->mnt.mnt_flags |= MNT_LOCK_NOEXEC;
         }
 
         /* Don't allow unprivileged users to reveal what is under a mount */
         if ((flag & CL_UNPRIVILEGED) &&
             (!(flag & CL_EXPIRE) || list_empty(&old->mnt_expire)))
                 mnt->mnt.mnt_flags |= MNT_LOCKED;
 
         atomic_inc(&sb->s_active);
         mnt->mnt.mnt_sb = sb;
         mnt->mnt.mnt_root = dget(root);
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         mnt->mnt_parent = mnt;
         lock_mount_hash();
         list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
         unlock_mount_hash();
 
         if ((flag & CL_SLAVE) ||
             ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
                 list_add(&mnt->mnt_slave, &old->mnt_slave_list);
                 mnt->mnt_master = old;
                 CLEAR_MNT_SHARED(mnt);
         } else if (!(flag & CL_PRIVATE)) {
                 if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
                         list_add(&mnt->mnt_share, &old->mnt_share);
                 if (IS_MNT_SLAVE(old))
                         list_add(&mnt->mnt_slave, &old->mnt_slave);
                 mnt->mnt_master = old->mnt_master;
         }
         if (flag & CL_MAKE_SHARED)
                 set_mnt_shared(mnt);
 
         /* stick the duplicate mount on the same expiry list
          * as the original if that was on one */
         if (flag & CL_EXPIRE) {
                 if (!list_empty(&old->mnt_expire))
                         list_add(&mnt->mnt_expire, &old->mnt_expire);
         }
 
         return mnt;
 
  out_free:
         mnt_free_id(mnt);
         free_vfsmnt(mnt);
         return ERR_PTR(err);
 }
 
 static void cleanup_mnt(struct mount *mnt)
 {
         /*
          * This probably indicates that somebody messed
          * up a mnt_want/drop_write() pair.  If this
          * happens, the filesystem was probably unable
          * to make r/w->r/o transitions.
          */
         /*
          * The locking used to deal with mnt_count decrement provides barriers,
          * so mnt_get_writers() below is safe.
          */
         WARN_ON(mnt_get_writers(mnt));
         if (unlikely(mnt->mnt_pins.first))
                 mnt_pin_kill(mnt);
         fsnotify_vfsmount_delete(&mnt->mnt);
         dput(mnt->mnt.mnt_root);
         deactivate_super(mnt->mnt.mnt_sb);
         mnt_free_id(mnt);
         call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
 }
 
 static void __cleanup_mnt(struct rcu_head *head)
 {
         cleanup_mnt(container_of(head, struct mount, mnt_rcu));
 }
 
 static LLIST_HEAD(delayed_mntput_list);
 static void delayed_mntput(struct work_struct *unused)
 {
         struct llist_node *node = llist_del_all(&delayed_mntput_list);
         struct llist_node *next;
 
         for (; node; node = next) {
                 next = llist_next(node);
                 cleanup_mnt(llist_entry(node, struct mount, mnt_llist));
         }
 }
 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
 
 static void mntput_no_expire(struct mount *mnt)
 {
         rcu_read_lock();
         mnt_add_count(mnt, -1);
         if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
                 rcu_read_unlock();
                 return;
         }
         lock_mount_hash();
         if (mnt_get_count(mnt)) {
                 rcu_read_unlock();
                 unlock_mount_hash();
                 return;
         }
         if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
                 rcu_read_unlock();
                 unlock_mount_hash();
                 return;
         }
         mnt->mnt.mnt_flags |= MNT_DOOMED;
         rcu_read_unlock();
 
         list_del(&mnt->mnt_instance);
 
         if (unlikely(!list_empty(&mnt->mnt_mounts))) {
                 struct mount *p, *tmp;
                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
                         umount_mnt(p);
                 }
         }
         unlock_mount_hash();
 
         if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
                 struct task_struct *task = current;
                 if (likely(!(task->flags & PF_KTHREAD))) {
                         init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
                         if (!task_work_add(task, &mnt->mnt_rcu, true))
                                 return;
                 }
                 if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
                         schedule_delayed_work(&delayed_mntput_work, 1);
                 return;
         }
         cleanup_mnt(mnt);
 }
 
 void mntput(struct vfsmount *mnt)
 {
         if (mnt) {
                 struct mount *m = real_mount(mnt);
                 /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
                 if (unlikely(m->mnt_expiry_mark))
                         m->mnt_expiry_mark = 0;
                 mntput_no_expire(m);
         }
 }
 EXPORT_SYMBOL(mntput);
 
 struct vfsmount *mntget(struct vfsmount *mnt)
 {
         if (mnt)
                 mnt_add_count(real_mount(mnt), 1);
         return mnt;
 }
 EXPORT_SYMBOL(mntget);
 
 struct vfsmount *mnt_clone_internal(struct path *path)
 {
         struct mount *p;
         p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
         if (IS_ERR(p))
                 return ERR_CAST(p);
         p->mnt.mnt_flags |= MNT_INTERNAL;
         return &p->mnt;
 }
 
 static inline void mangle(struct seq_file *m, const char *s)
 {
         seq_escape(m, s, " \t\n\\");
 }
 
 /*
  * Simple .show_options callback for filesystems which don't want to
  * implement more complex mount option showing.
  *
  * See also save_mount_options().
  */
 int generic_show_options(struct seq_file *m, struct dentry *root)
 {
         const char *options;
 
         rcu_read_lock();
         options = rcu_dereference(root->d_sb->s_options);
 
         if (options != NULL && options[0]) {
                 seq_putc(m, ',');
                 mangle(m, options);
         }
         rcu_read_unlock();
 
         return 0;
 }
 EXPORT_SYMBOL(generic_show_options);
 
 /*
  * If filesystem uses generic_show_options(), this function should be
  * called from the fill_super() callback.
  *
  * The .remount_fs callback usually needs to be handled in a special
  * way, to make sure, that previous options are not overwritten if the
  * remount fails.
  *
  * Also note, that if the filesystem's .remount_fs function doesn't
  * reset all options to their default value, but changes only newly
  * given options, then the displayed options will not reflect reality
  * any more.
  */
 void save_mount_options(struct super_block *sb, char *options)
 {
         BUG_ON(sb->s_options);
         rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
 }
 EXPORT_SYMBOL(save_mount_options);
 
 void replace_mount_options(struct super_block *sb, char *options)
 {
         char *old = sb->s_options;
         rcu_assign_pointer(sb->s_options, options);
         if (old) {
                 synchronize_rcu();
                 kfree(old);
         }
 }
 EXPORT_SYMBOL(replace_mount_options);
 
 #ifdef CONFIG_PROC_FS
 /* iterator; we want it to have access to namespace_sem, thus here... */
 static void *m_start(struct seq_file *m, loff_t *pos)
 {
         struct proc_mounts *p = proc_mounts(m);
 
         down_read(&namespace_sem);
         if (p->cached_event == p->ns->event) {
                 void *v = p->cached_mount;
                 if (*pos == p->cached_index)
                         return v;
                 if (*pos == p->cached_index + 1) {
                         v = seq_list_next(v, &p->ns->list, &p->cached_index);
                         return p->cached_mount = v;
                 }
         }
 
         p->cached_event = p->ns->event;
         p->cached_mount = seq_list_start(&p->ns->list, *pos);
         p->cached_index = *pos;
         return p->cached_mount;
 }
 
 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 {
         struct proc_mounts *p = proc_mounts(m);
 
         p->cached_mount = seq_list_next(v, &p->ns->list, pos);
         p->cached_index = *pos;
         return p->cached_mount;
 }
 
 static void m_stop(struct seq_file *m, void *v)
 {
         up_read(&namespace_sem);
 }
 
 static int m_show(struct seq_file *m, void *v)
 {
         struct proc_mounts *p = proc_mounts(m);
         struct mount *r = list_entry(v, struct mount, mnt_list);
         return p->show(m, &r->mnt);
 }
 
 const struct seq_operations mounts_op = {
         .start  = m_start,
         .next   = m_next,
         .stop   = m_stop,
         .show   = m_show,
 };
 #endif  /* CONFIG_PROC_FS */
 
 /**
  * may_umount_tree - check if a mount tree is busy
  * @mnt: root of mount tree
  *
  * This is called to check if a tree of mounts has any
  * open files, pwds, chroots or sub mounts that are
  * busy.
  */
 int may_umount_tree(struct vfsmount *m)
 {
         struct mount *mnt = real_mount(m);
         int actual_refs = 0;
         int minimum_refs = 0;
         struct mount *p;
         BUG_ON(!m);
 
         /* write lock needed for mnt_get_count */
         lock_mount_hash();
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 actual_refs += mnt_get_count(p);
                 minimum_refs += 2;
         }
         unlock_mount_hash();
 
         if (actual_refs > minimum_refs)
                 return 0;
 
         return 1;
 }
 
 EXPORT_SYMBOL(may_umount_tree);
 
 /**
  * may_umount - check if a mount point is busy
  * @mnt: root of mount
  *
  * This is called to check if a mount point has any
  * open files, pwds, chroots or sub mounts. If the
  * mount has sub mounts this will return busy
  * regardless of whether the sub mounts are busy.
  *
  * Doesn't take quota and stuff into account. IOW, in some cases it will
  * give false negatives. The main reason why it's here is that we need
  * a non-destructive way to look for easily umountable filesystems.
  */
 int may_umount(struct vfsmount *mnt)
 {
         int ret = 1;
         down_read(&namespace_sem);
         lock_mount_hash();
         if (propagate_mount_busy(real_mount(mnt), 2))
                 ret = 0;
         unlock_mount_hash();
         up_read(&namespace_sem);
         return ret;
 }
 
 EXPORT_SYMBOL(may_umount);
 
 static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
 
 static void namespace_unlock(void)
 {
         struct hlist_head head = unmounted;
 
         if (likely(hlist_empty(&head))) {
                 up_write(&namespace_sem);
                 return;
         }
 
         head.first->pprev = &head.first;
         INIT_HLIST_HEAD(&unmounted);
         up_write(&namespace_sem);
 
         synchronize_rcu();
 
         group_pin_kill(&head);
 }
 
 static inline void namespace_lock(void)
 {
         down_write(&namespace_sem);
 }
 
 enum umount_tree_flags {
         UMOUNT_SYNC = 1,
         UMOUNT_PROPAGATE = 2,
         UMOUNT_CONNECTED = 4,
 };
 /*
  * mount_lock must be held
  * namespace_sem must be held for write
  */
 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 {
         LIST_HEAD(tmp_list);
         struct mount *p;
 
         if (how & UMOUNT_PROPAGATE)
                 propagate_mount_unlock(mnt);
 
         /* Gather the mounts to umount */
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 p->mnt.mnt_flags |= MNT_UMOUNT;
                 list_move(&p->mnt_list, &tmp_list);
         }
 
         /* Hide the mounts from mnt_mounts */
         list_for_each_entry(p, &tmp_list, mnt_list) {
                 list_del_init(&p->mnt_child);
         }
 
         /* Add propogated mounts to the tmp_list */
         if (how & UMOUNT_PROPAGATE)
                 propagate_umount(&tmp_list);
 
         while (!list_empty(&tmp_list)) {
                 bool disconnect;
                 p = list_first_entry(&tmp_list, struct mount, mnt_list);
                 list_del_init(&p->mnt_expire);
                 list_del_init(&p->mnt_list);
                 __touch_mnt_namespace(p->mnt_ns);
                 p->mnt_ns = NULL;
                 if (how & UMOUNT_SYNC)
                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
                 disconnect = !(((how & UMOUNT_CONNECTED) &&
                                 mnt_has_parent(p) &&
                                 (p->mnt_parent->mnt.mnt_flags & MNT_UMOUNT)) ||
                                IS_MNT_LOCKED_AND_LAZY(p));
 
                 pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
                                  disconnect ? &unmounted : NULL);
                 if (mnt_has_parent(p)) {
                         mnt_add_count(p->mnt_parent, -1);
                         if (!disconnect) {
                                 /* Don't forget about p */
                                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
                         } else {
                                 umount_mnt(p);
                         }
                 }
                 change_mnt_propagation(p, MS_PRIVATE);
         }
 }
 
 static void shrink_submounts(struct mount *mnt);
 
 static int do_umount(struct mount *mnt, int flags)
 {
         struct super_block *sb = mnt->mnt.mnt_sb;
         int retval;
 
         retval = security_sb_umount(&mnt->mnt, flags);
         if (retval)
                 return retval;
 
         /*
          * Allow userspace to request a mountpoint be expired rather than
          * unmounting unconditionally. Unmount only happens if:
          *  (1) the mark is already set (the mark is cleared by mntput())
          *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
          */
         if (flags & MNT_EXPIRE) {
                 if (&mnt->mnt == current->fs->root.mnt ||
                     flags & (MNT_FORCE | MNT_DETACH))
                         return -EINVAL;
 
                 /*
                  * probably don't strictly need the lock here if we examined
                  * all race cases, but it's a slowpath.
                  */
                 lock_mount_hash();
                 if (mnt_get_count(mnt) != 2) {
                         unlock_mount_hash();
                         return -EBUSY;
                 }
                 unlock_mount_hash();
 
                 if (!xchg(&mnt->mnt_expiry_mark, 1))
                         return -EAGAIN;
         }
 
         /*
          * If we may have to abort operations to get out of this
          * mount, and they will themselves hold resources we must
          * allow the fs to do things. In the Unix tradition of
          * 'Gee thats tricky lets do it in userspace' the umount_begin
          * might fail to complete on the first run through as other tasks
          * must return, and the like. Thats for the mount program to worry
          * about for the moment.
          */
 
         if (flags & MNT_FORCE && sb->s_op->umount_begin) {
                 sb->s_op->umount_begin(sb);
         }
 
         /*
          * No sense to grab the lock for this test, but test itself looks
          * somewhat bogus. Suggestions for better replacement?
          * Ho-hum... In principle, we might treat that as umount + switch
          * to rootfs. GC would eventually take care of the old vfsmount.
          * Actually it makes sense, especially if rootfs would contain a
          * /reboot - static binary that would close all descriptors and
          * call reboot(9). Then init(8) could umount root and exec /reboot.
          */
         if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
                 /*
                  * Special case for "unmounting" root ...
                  * we just try to remount it readonly.
                  */
                 if (!capable(CAP_SYS_ADMIN))
                         return -EPERM;
                 down_write(&sb->s_umount);
                 if (!(sb->s_flags & MS_RDONLY))
                         retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
                 up_write(&sb->s_umount);
                 return retval;
         }
 
         namespace_lock();
         lock_mount_hash();
         event++;
 
         if (flags & MNT_DETACH) {
                 if (!list_empty(&mnt->mnt_list))
                         umount_tree(mnt, UMOUNT_PROPAGATE);
                 retval = 0;
         } else {
                 shrink_submounts(mnt);
                 retval = -EBUSY;
                 if (!propagate_mount_busy(mnt, 2)) {
                         if (!list_empty(&mnt->mnt_list))
                                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
                         retval = 0;
                 }
         }
         unlock_mount_hash();
         namespace_unlock();
         return retval;
 }
 
 /*
  * __detach_mounts - lazily unmount all mounts on the specified dentry
  *
  * During unlink, rmdir, and d_drop it is possible to loose the path
  * to an existing mountpoint, and wind up leaking the mount.
  * detach_mounts allows lazily unmounting those mounts instead of
  * leaking them.
  *
  * The caller may hold dentry->d_inode->i_mutex.
  */
 void __detach_mounts(struct dentry *dentry)
 {
         struct mountpoint *mp;
         struct mount *mnt;
 
         namespace_lock();
         mp = lookup_mountpoint(dentry);
         if (IS_ERR_OR_NULL(mp))
                 goto out_unlock;
 
         lock_mount_hash();
         while (!hlist_empty(&mp->m_list)) {
                 mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
                 if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
                         struct mount *p, *tmp;
                         list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
                                 hlist_add_head(&p->mnt_umount.s_list, &unmounted);
                                 umount_mnt(p);
                         }
                 }
                 else umount_tree(mnt, UMOUNT_CONNECTED);
         }
         unlock_mount_hash();
         put_mountpoint(mp);
 out_unlock:
         namespace_unlock();
 }
 
 /* 
  * Is the caller allowed to modify his namespace?
  */
 static inline bool may_mount(void)
 {
         return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
 }
 
 /*
  * Now umount can handle mount points as well as block devices.
  * This is important for filesystems which use unnamed block devices.
  *
  * We now support a flag for forced unmount like the other 'big iron'
  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
  */
 
 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 {
         struct path path;
         struct mount *mnt;
         int retval;
         int lookup_flags = 0;
 
         if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
                 return -EINVAL;
 
         if (!may_mount())
                 return -EPERM;
 
         if (!(flags & UMOUNT_NOFOLLOW))
                 lookup_flags |= LOOKUP_FOLLOW;
 
         retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
         if (retval)
                 goto out;
         mnt = real_mount(path.mnt);
         retval = -EINVAL;
         if (path.dentry != path.mnt->mnt_root)
                 goto dput_and_out;
         if (!check_mnt(mnt))
                 goto dput_and_out;
         if (mnt->mnt.mnt_flags & MNT_LOCKED)
                 goto dput_and_out;
         retval = -EPERM;
         if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
                 goto dput_and_out;
 
         retval = do_umount(mnt, flags);
 dput_and_out:
         /* we mustn't call path_put() as that would clear mnt_expiry_mark */
         dput(path.dentry);
         mntput_no_expire(mnt);
 out:
         return retval;
 }
 
 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
 
 /*
  *      The 2.0 compatible umount. No flags.
  */
 SYSCALL_DEFINE1(oldumount, char __user *, name)
 {
         return sys_umount(name, 0);
 }
 
 #endif
 
 static bool is_mnt_ns_file(struct dentry *dentry)
 {
         /* Is this a proxy for a mount namespace? */
         return dentry->d_op == &ns_dentry_operations &&
                dentry->d_fsdata == &mntns_operations;
 }
 
 struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
 {
         return container_of(ns, struct mnt_namespace, ns);
 }
 
 static bool mnt_ns_loop(struct dentry *dentry)
 {
         /* Could bind mounting the mount namespace inode cause a
          * mount namespace loop?
          */
         struct mnt_namespace *mnt_ns;
         if (!is_mnt_ns_file(dentry))
                 return false;
 
         mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
         return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
 }
 
 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
                                         int flag)
 {
         struct mount *res, *p, *q, *r, *parent;
 
         if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
                 return ERR_PTR(-EINVAL);
 
         if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
                 return ERR_PTR(-EINVAL);
 
         res = q = clone_mnt(mnt, dentry, flag);
         if (IS_ERR(q))
                 return q;
 
         q->mnt_mountpoint = mnt->mnt_mountpoint;
 
         p = mnt;
         list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
                 struct mount *s;
                 if (!is_subdir(r->mnt_mountpoint, dentry))
                         continue;
 
                 for (s = r; s; s = next_mnt(s, r)) {
                         struct mount *t = NULL;
                         if (!(flag & CL_COPY_UNBINDABLE) &&
                             IS_MNT_UNBINDABLE(s)) {
                                 s = skip_mnt_tree(s);
                                 continue;
                         }
                         if (!(flag & CL_COPY_MNT_NS_FILE) &&
                             is_mnt_ns_file(s->mnt.mnt_root)) {
                                 s = skip_mnt_tree(s);
                                 continue;
                         }
                         while (p != s->mnt_parent) {
                                 p = p->mnt_parent;
                                 q = q->mnt_parent;
                         }
                         p = s;
                         parent = q;
                         q = clone_mnt(p, p->mnt.mnt_root, flag);
                         if (IS_ERR(q))
                                 goto out;
                         lock_mount_hash();
                         list_add_tail(&q->mnt_list, &res->mnt_list);
                         mnt_set_mountpoint(parent, p->mnt_mp, q);
                         if (!list_empty(&parent->mnt_mounts)) {
                                 t = list_last_entry(&parent->mnt_mounts,
                                         struct mount, mnt_child);
                                 if (t->mnt_mp != p->mnt_mp)
                                         t = NULL;
                         }
                         attach_shadowed(q, parent, t);
                         unlock_mount_hash();
                 }
         }
         return res;
 out:
         if (res) {
                 lock_mount_hash();
                 umount_tree(res, UMOUNT_SYNC);
                 unlock_mount_hash();
         }
         return q;
 }
 
 /* Caller should check returned pointer for errors */
 
 struct vfsmount *collect_mounts(struct path *path)
 {
         struct mount *tree;
         namespace_lock();
         if (!check_mnt(real_mount(path->mnt)))
                 tree = ERR_PTR(-EINVAL);
         else
                 tree = copy_tree(real_mount(path->mnt), path->dentry,
                                  CL_COPY_ALL | CL_PRIVATE);
         namespace_unlock();
         if (IS_ERR(tree))
                 return ERR_CAST(tree);
         return &tree->mnt;
 }
 
 void drop_collected_mounts(struct vfsmount *mnt)
 {
         namespace_lock();
         lock_mount_hash();
         umount_tree(real_mount(mnt), UMOUNT_SYNC);
         unlock_mount_hash();
         namespace_unlock();
 }
 
 /**
  * clone_private_mount - create a private clone of a path
  *
  * This creates a new vfsmount, which will be the clone of @path.  The new will
  * not be attached anywhere in the namespace and will be private (i.e. changes
  * to the originating mount won't be propagated into this).
  *
  * Release with mntput().
  */
 struct vfsmount *clone_private_mount(struct path *path)
 {
         struct mount *old_mnt = real_mount(path->mnt);
         struct mount *new_mnt;
 
         if (IS_MNT_UNBINDABLE(old_mnt))
                 return ERR_PTR(-EINVAL);
 
         down_read(&namespace_sem);
         new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
         up_read(&namespace_sem);
         if (IS_ERR(new_mnt))
                 return ERR_CAST(new_mnt);
 
         return &new_mnt->mnt;
 }
 EXPORT_SYMBOL_GPL(clone_private_mount);
 
 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
                    struct vfsmount *root)
 {
         struct mount *mnt;
         int res = f(root, arg);
         if (res)
                 return res;
         list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
                 res = f(&mnt->mnt, arg);
                 if (res)
                         return res;
         }
         return 0;
 }
 
 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
 {
         struct mount *p;
 
         for (p = mnt; p != end; p = next_mnt(p, mnt)) {
                 if (p->mnt_group_id && !IS_MNT_SHARED(p))
                         mnt_release_group_id(p);
         }
 }
 
 static int invent_group_ids(struct mount *mnt, bool recurse)
 {
         struct mount *p;
 
         for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
                 if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
                         int err = mnt_alloc_group_id(p);
                         if (err) {
                                 cleanup_group_ids(mnt, p);
                                 return err;
                         }
                 }
         }
 
         return 0;
 }
 
 /*
  *  @source_mnt : mount tree to be attached
  *  @nd         : place the mount tree @source_mnt is attached
  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
  *                 store the parent mount and mountpoint dentry.
  *                 (done when source_mnt is moved)
  *
  *  NOTE: in the table below explains the semantics when a source mount
  *  of a given type is attached to a destination mount of a given type.
  * ---------------------------------------------------------------------------
  * |         BIND MOUNT OPERATION                                            |
  * |**************************************************************************
  * | source-->| shared        |       private  |       slave    | unbindable |
  * | dest     |               |                |                |            |
  * |   |      |               |                |                |            |
  * |   v      |               |                |                |            |
  * |**************************************************************************
  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
  * |          |               |                |                |            |
  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
  * ***************************************************************************
  * A bind operation clones the source mount and mounts the clone on the
  * destination mount.
  *
  * (++)  the cloned mount is propagated to all the mounts in the propagation
  *       tree of the destination mount and the cloned mount is added to
  *       the peer group of the source mount.
  * (+)   the cloned mount is created under the destination mount and is marked
  *       as shared. The cloned mount is added to the peer group of the source
  *       mount.
  * (+++) the mount is propagated to all the mounts in the propagation tree
  *       of the destination mount and the cloned mount is made slave
  *       of the same master as that of the source mount. The cloned mount
  *       is marked as 'shared and slave'.
  * (*)   the cloned mount is made a slave of the same master as that of the
  *       source mount.
  *
  * ---------------------------------------------------------------------------
  * |                    MOVE MOUNT OPERATION                                 |
  * |**************************************************************************
  * | source-->| shared        |       private  |       slave    | unbindable |
  * | dest     |               |                |                |            |
  * |   |      |               |                |                |            |
  * |   v      |               |                |                |            |
  * |**************************************************************************
  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
  * |          |               |                |                |            |
  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
  * ***************************************************************************
  *
  * (+)  the mount is moved to the destination. And is then propagated to
  *      all the mounts in the propagation tree of the destination mount.
  * (+*)  the mount is moved to the destination.
  * (+++)  the mount is moved to the destination and is then propagated to
  *      all the mounts belonging to the destination mount's propagation tree.
  *      the mount is marked as 'shared and slave'.
  * (*)  the mount continues to be a slave at the new location.
  *
  * if the source mount is a tree, the operations explained above is
  * applied to each mount in the tree.
  * Must be called without spinlocks held, since this function can sleep
  * in allocations.
  */
 static int attach_recursive_mnt(struct mount *source_mnt,
                         struct mount *dest_mnt,
                         struct mountpoint *dest_mp,
                         struct path *parent_path)
 {
         HLIST_HEAD(tree_list);
         struct mount *child, *p;
         struct hlist_node *n;
         int err;
 
         if (IS_MNT_SHARED(dest_mnt)) {
                 err = invent_group_ids(source_mnt, true);
                 if (err)
                         goto out;
                 err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
                 lock_mount_hash();
                 if (err)
                         goto out_cleanup_ids;
                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
                         set_mnt_shared(p);
         } else {
                 lock_mount_hash();
         }
         if (parent_path) {
                 detach_mnt(source_mnt, parent_path);
                 attach_mnt(source_mnt, dest_mnt, dest_mp);
                 touch_mnt_namespace(source_mnt->mnt_ns);
         } else {
                 mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
                 commit_tree(source_mnt, NULL);
         }
 
         hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
                 struct mount *q;
                 hlist_del_init(&child->mnt_hash);
                 q = __lookup_mnt_last(&child->mnt_parent->mnt,
                                       child->mnt_mountpoint);
                 commit_tree(child, q);
         }
         unlock_mount_hash();
 
         return 0;
 
  out_cleanup_ids:
         while (!hlist_empty(&tree_list)) {
                 child = hlist_entry(tree_list.first, struct mount, mnt_hash);
                 umount_tree(child, UMOUNT_SYNC);
         }
         unlock_mount_hash();
         cleanup_group_ids(source_mnt, NULL);
  out:
         return err;
 }
 
 static struct mountpoint *lock_mount(struct path *path)
 {
         struct vfsmount *mnt;
         struct dentry *dentry = path->dentry;
 retry:
         mutex_lock(&dentry->d_inode->i_mutex);
         if (unlikely(cant_mount(dentry))) {
                 mutex_unlock(&dentry->d_inode->i_mutex);
                 return ERR_PTR(-ENOENT);
         }
         namespace_lock();
         mnt = lookup_mnt(path);
         if (likely(!mnt)) {
                 struct mountpoint *mp = lookup_mountpoint(dentry);
                 if (!mp)
                         mp = new_mountpoint(dentry);
                 if (IS_ERR(mp)) {
                         namespace_unlock();
                         mutex_unlock(&dentry->d_inode->i_mutex);
                         return mp;
                 }
                 return mp;
         }
         namespace_unlock();
         mutex_unlock(&path->dentry->d_inode->i_mutex);
         path_put(path);
         path->mnt = mnt;
         dentry = path->dentry = dget(mnt->mnt_root);
         goto retry;
 }
 
 static void unlock_mount(struct mountpoint *where)
 {
         struct dentry *dentry = where->m_dentry;
         put_mountpoint(where);
         namespace_unlock();
         mutex_unlock(&dentry->d_inode->i_mutex);
 }
 
 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
 {
         if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
                 return -EINVAL;
 
         if (d_is_dir(mp->m_dentry) !=
               d_is_dir(mnt->mnt.mnt_root))
                 return -ENOTDIR;
 
         return attach_recursive_mnt(mnt, p, mp, NULL);
 }
 
 /*
  * Sanity check the flags to change_mnt_propagation.
  */
 
 static int flags_to_propagation_type(int flags)
 {
         int type = flags & ~(MS_REC | MS_SILENT);
 
         /* Fail if any non-propagation flags are set */
         if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
                 return 0;
         /* Only one propagation flag should be set */
         if (!is_power_of_2(type))
                 return 0;
         return type;
 }
 
 /*
  * recursively change the type of the mountpoint.
  */
 static int do_change_type(struct path *path, int flag)
 {
         struct mount *m;
         struct mount *mnt = real_mount(path->mnt);
         int recurse = flag & MS_REC;
         int type;
         int err = 0;
 
         if (path->dentry != path->mnt->mnt_root)
                 return -EINVAL;
 
         type = flags_to_propagation_type(flag);
         if (!type)
                 return -EINVAL;
 
         namespace_lock();
         if (type == MS_SHARED) {
                 err = invent_group_ids(mnt, recurse);
                 if (err)
                         goto out_unlock;
         }
 
         lock_mount_hash();
         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
                 change_mnt_propagation(m, type);
         unlock_mount_hash();
 
  out_unlock:
         namespace_unlock();
         return err;
 }
 
 static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
 {
         struct mount *child;
         list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
                 if (!is_subdir(child->mnt_mountpoint, dentry))
                         continue;
 
                 if (child->mnt.mnt_flags & MNT_LOCKED)
                         return true;
         }
         return false;
 }
 
 /*
  * do loopback mount.
  */
 static int do_loopback(struct path *path, const char *old_name,
                                 int recurse)
 {
         struct path old_path;
         struct mount *mnt = NULL, *old, *parent;
         struct mountpoint *mp;
         int err;
         if (!old_name || !*old_name)
                 return -EINVAL;
         err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
         if (err)
                 return err;
 
         err = -EINVAL;
         if (mnt_ns_loop(old_path.dentry))
                 goto out; 
 
         mp = lock_mount(path);
         err = PTR_ERR(mp);
         if (IS_ERR(mp))
                 goto out;
 
         old = real_mount(old_path.mnt);
         parent = real_mount(path->mnt);
 
         err = -EINVAL;
         if (IS_MNT_UNBINDABLE(old))
                 goto out2;
 
         if (!check_mnt(parent))
                 goto out2;
 
         if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations)
                 goto out2;
 
         if (!recurse && has_locked_children(old, old_path.dentry))
                 goto out2;
 
         if (recurse)
                 mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
         else
                 mnt = clone_mnt(old, old_path.dentry, 0);
 
         if (IS_ERR(mnt)) {
                 err = PTR_ERR(mnt);
                 goto out2;
         }
 
         mnt->mnt.mnt_flags &= ~MNT_LOCKED;
 
         err = graft_tree(mnt, parent, mp);
         if (err) {
                 lock_mount_hash();
                 umount_tree(mnt, UMOUNT_SYNC);
                 unlock_mount_hash();
         }
 out2:
         unlock_mount(mp);
 out:
         path_put(&old_path);
         return err;
 }
 
 static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
 {
         int error = 0;
         int readonly_request = 0;
 
         if (ms_flags & MS_RDONLY)
                 readonly_request = 1;
         if (readonly_request == __mnt_is_readonly(mnt))
                 return 0;
 
         if (readonly_request)
                 error = mnt_make_readonly(real_mount(mnt));
         else
                 __mnt_unmake_readonly(real_mount(mnt));
         return error;
 }
 
 /*
  * change filesystem flags. dir should be a physical root of filesystem.
  * If you've mounted a non-root directory somewhere and want to do remount
  * on it - tough luck.
  */
 static int do_remount(struct path *path, int flags, int mnt_flags,
                       void *data)
 {
         int err;
         struct super_block *sb = path->mnt->mnt_sb;
         struct mount *mnt = real_mount(path->mnt);
 
         if (!check_mnt(mnt))
                 return -EINVAL;
 
         if (path->dentry != path->mnt->mnt_root)
                 return -EINVAL;
 
         /* Don't allow changing of locked mnt flags.
          *
          * No locks need to be held here while testing the various
          * MNT_LOCK flags because those flags can never be cleared
          * once they are set.
          */
         if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
             !(mnt_flags & MNT_READONLY)) {
                 return -EPERM;
         }
         if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
             !(mnt_flags & MNT_NODEV)) {
                 /* Was the nodev implicitly added in mount? */
                 if ((mnt->mnt_ns->user_ns != &init_user_ns) &&
                     !(sb->s_type->fs_flags & FS_USERNS_DEV_MOUNT)) {
                         mnt_flags |= MNT_NODEV;
                 } else {
                         return -EPERM;
                 }
         }
         if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&
             !(mnt_flags & MNT_NOSUID)) {
                 return -EPERM;
         }
         if ((mnt->mnt.mnt_flags & MNT_LOCK_NOEXEC) &&
             !(mnt_flags & MNT_NOEXEC)) {
                 return -EPERM;
         }
         if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
             ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK))) {
                 return -EPERM;
         }
 
         err = security_sb_remount(sb, data);
         if (err)
                 return err;
 
         down_write(&sb->s_umount);
         if (flags & MS_BIND)
                 err = change_mount_flags(path->mnt, flags);
         else if (!capable(CAP_SYS_ADMIN))
                 err = -EPERM;
         else
                 err = do_remount_sb(sb, flags, data, 0);
         if (!err) {
                 lock_mount_hash();
                 mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
                 mnt->mnt.mnt_flags = mnt_flags;
                 touch_mnt_namespace(mnt->mnt_ns);
                 unlock_mount_hash();
         }
         up_write(&sb->s_umount);
         return err;
 }
 
 static inline int tree_contains_unbindable(struct mount *mnt)
 {
         struct mount *p;
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 if (IS_MNT_UNBINDABLE(p))
                         return 1;
         }
         return 0;
 }
 
 static int do_move_mount(struct path *path, const char *old_name)
 {
         struct path old_path, parent_path;
         struct mount *p;
         struct mount *old;
         struct mountpoint *mp;
         int err;
         if (!old_name || !*old_name)
                 return -EINVAL;
         err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
         if (err)
                 return err;
 
         mp = lock_mount(path);
         err = PTR_ERR(mp);
         if (IS_ERR(mp))
                 goto out;
 
         old = real_mount(old_path.mnt);
         p = real_mount(path->mnt);
 
         err = -EINVAL;
         if (!check_mnt(p) || !check_mnt(old))
                 goto out1;
 
         if (old->mnt.mnt_flags & MNT_LOCKED)
                 goto out1;
 
         err = -EINVAL;
         if (old_path.dentry != old_path.mnt->mnt_root)
                 goto out1;
 
         if (!mnt_has_parent(old))
                 goto out1;
 
         if (d_is_dir(path->dentry) !=
               d_is_dir(old_path.dentry))
                 goto out1;
         /*
          * Don't move a mount residing in a shared parent.
          */
         if (IS_MNT_SHARED(old->mnt_parent))
                 goto out1;
         /*
          * Don't move a mount tree containing unbindable mounts to a destination
          * mount which is shared.
          */
         if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
                 goto out1;
         err = -ELOOP;
         for (; mnt_has_parent(p); p = p->mnt_parent)
                 if (p == old)
                         goto out1;
 
         err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
         if (err)
                 goto out1;
 
         /* if the mount is moved, it should no longer be expire
          * automatically */
         list_del_init(&old->mnt_expire);
 out1:
         unlock_mount(mp);
 out:
         if (!err)
                 path_put(&parent_path);
         path_put(&old_path);
         return err;
 }
 
 static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
 {
         int err;
         const char *subtype = strchr(fstype, '.');
         if (subtype) {
                 subtype++;
                 err = -EINVAL;
                 if (!subtype[0])
                         goto err;
         } else
                 subtype = "";
 
         mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
         err = -ENOMEM;
         if (!mnt->mnt_sb->s_subtype)
                 goto err;
         return mnt;
 
  err:
         mntput(mnt);
         return ERR_PTR(err);
 }
 
 /*
  * add a mount into a namespace's mount tree
  */
 static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
 {
         struct mountpoint *mp;
         struct mount *parent;
         int err;
 
         mnt_flags &= ~MNT_INTERNAL_FLAGS;
 
         mp = lock_mount(path);
         if (IS_ERR(mp))
                 return PTR_ERR(mp);
 
         parent = real_mount(path->mnt);
         err = -EINVAL;
         if (unlikely(!check_mnt(parent))) {
                 /* that's acceptable only for automounts done in private ns */
                 if (!(mnt_flags & MNT_SHRINKABLE))
                         goto unlock;
                 /* ... and for those we'd better have mountpoint still alive */
                 if (!parent->mnt_ns)
                         goto unlock;
         }
 
         /* Refuse the same filesystem on the same mount point */
         err = -EBUSY;
         if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
             path->mnt->mnt_root == path->dentry)
                 goto unlock;
 
         err = -EINVAL;
         if (d_is_symlink(newmnt->mnt.mnt_root))
                 goto unlock;
 
         newmnt->mnt.mnt_flags = mnt_flags;
         err = graft_tree(newmnt, parent, mp);
 
 unlock:
         unlock_mount(mp);
         return err;
 }
 
 static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
 
 /*
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
 static int do_new_mount(struct path *path, const char *fstype, int flags,
                         int mnt_flags, const char *name, void *data)
 {
         struct file_system_type *type;
         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
         struct vfsmount *mnt;
         int err;
 
         if (!fstype)
                 return -EINVAL;
 
         type = get_fs_type(fstype);
         if (!type)
                 return -ENODEV;
 
         if (user_ns != &init_user_ns) {
                 if (!(type->fs_flags & FS_USERNS_MOUNT)) {
                         put_filesystem(type);
                         return -EPERM;
                 }
                 /* Only in special cases allow devices from mounts
                  * created outside the initial user namespace.
                  */
                 if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
                         flags |= MS_NODEV;
                         mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
                 }
                 if (type->fs_flags & FS_USERNS_VISIBLE) {
                         if (!fs_fully_visible(type, &mnt_flags))
                                 return -EPERM;
                 }
         }
 
         mnt = vfs_kern_mount(type, flags, name, data);
         if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
             !mnt->mnt_sb->s_subtype)
                 mnt = fs_set_subtype(mnt, fstype);
 
         put_filesystem(type);
         if (IS_ERR(mnt))
                 return PTR_ERR(mnt);
 
         err = do_add_mount(real_mount(mnt), path, mnt_flags);
         if (err)
                 mntput(mnt);
         return err;
 }
 
 int finish_automount(struct vfsmount *m, struct path *path)
 {
         struct mount *mnt = real_mount(m);
         int err;
         /* The new mount record should have at least 2 refs to prevent it being
          * expired before we get a chance to add it
          */
         BUG_ON(mnt_get_count(mnt) < 2);
 
         if (m->mnt_sb == path->mnt->mnt_sb &&
             m->mnt_root == path->dentry) {
                 err = -ELOOP;
                 goto fail;
         }
 
         err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
         if (!err)
                 return 0;
 fail:
         /* remove m from any expiration list it may be on */
         if (!list_empty(&mnt->mnt_expire)) {
                 namespace_lock();
                 list_del_init(&mnt->mnt_expire);
                 namespace_unlock();
         }
         mntput(m);
         mntput(m);
         return err;
 }
 
 /**
  * mnt_set_expiry - Put a mount on an expiration list
  * @mnt: The mount to list.
  * @expiry_list: The list to add the mount to.
  */
 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
 {
         namespace_lock();
 
         list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
 
         namespace_unlock();
 }
 EXPORT_SYMBOL(mnt_set_expiry);
 
 /*
  * process a list of expirable mountpoints with the intent of discarding any
  * mountpoints that aren't in use and haven't been touched since last we came
  * here
  */
 void mark_mounts_for_expiry(struct list_head *mounts)
 {
         struct mount *mnt, *next;
         LIST_HEAD(graveyard);
 
         if (list_empty(mounts))
                 return;
 
         namespace_lock();
         lock_mount_hash();
 
         /* extract from the expiration list every vfsmount that matches the
          * following criteria:
          * - only referenced by its parent vfsmount
          * - still marked for expiry (marked on the last call here; marks are
          *   cleared by mntput())
          */
         list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
                 if (!xchg(&mnt->mnt_expiry_mark, 1) ||
                         propagate_mount_busy(mnt, 1))
                         continue;
                 list_move(&mnt->mnt_expire, &graveyard);
         }
         while (!list_empty(&graveyard)) {
                 mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
                 touch_mnt_namespace(mnt->mnt_ns);
                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
         }
         unlock_mount_hash();
         namespace_unlock();
 }
 
 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
 
 /*
  * Ripoff of 'select_parent()'
  *
  * search the list of submounts for a given mountpoint, and move any
  * shrinkable submounts to the 'graveyard' list.
  */
 static int select_submounts(struct mount *parent, struct list_head *graveyard)
 {
         struct mount *this_parent = parent;
         struct list_head *next;
         int found = 0;
 
 repeat:
         next = this_parent->mnt_mounts.next;
 resume:
         while (next != &this_parent->mnt_mounts) {
                 struct list_head *tmp = next;
                 struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
 
                 next = tmp->next;
                 if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
                         continue;
                 /*
                  * Descend a level if the d_mounts list is non-empty.
                  */
                 if (!list_empty(&mnt->mnt_mounts)) {
                         this_parent = mnt;
                         goto repeat;
                 }
 
                 if (!propagate_mount_busy(mnt, 1)) {
                         list_move_tail(&mnt->mnt_expire, graveyard);
                         found++;
                 }
         }
         /*
          * All done at this level ... ascend and resume the search
          */
         if (this_parent != parent) {
                 next = this_parent->mnt_child.next;
                 this_parent = this_parent->mnt_parent;
                 goto resume;
         }
         return found;
 }
 
 /*
  * process a list of expirable mountpoints with the intent of discarding any
  * submounts of a specific parent mountpoint
  *
  * mount_lock must be held for write
  */
 static void shrink_submounts(struct mount *mnt)
 {
         LIST_HEAD(graveyard);
         struct mount *m;
 
         /* extract submounts of 'mountpoint' from the expiration list */
         while (select_submounts(mnt, &graveyard)) {
                 while (!list_empty(&graveyard)) {
                         m = list_first_entry(&graveyard, struct mount,
                                                 mnt_expire);
                         touch_mnt_namespace(m->mnt_ns);
                         umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
                 }
         }
 }
 
 /*
  * Some copy_from_user() implementations do not return the exact number of
  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
  * Note that this function differs from copy_from_user() in that it will oops
  * on bad values of `to', rather than returning a short copy.
  */
 static long exact_copy_from_user(void *to, const void __user * from,
                                  unsigned long n)
 {
         char *t = to;
         const char __user *f = from;
         char c;
 
         if (!access_ok(VERIFY_READ, from, n))
                 return n;
 
         while (n) {
                 if (__get_user(c, f)) {
                         memset(t, 0, n);
                         break;
                 }
                 *t++ = c;
                 f++;
                 n--;
         }
         return n;
 }
 
 int copy_mount_options(const void __user * data, unsigned long *where)
 {
         int i;
         unsigned long page;
         unsigned long size;
 
         *where = 0;
         if (!data)
                 return 0;
 
         if (!(page = __get_free_page(GFP_KERNEL)))
                 return -ENOMEM;
 
         /* We only care that *some* data at the address the user
          * gave us is valid.  Just in case, we'll zero
          * the remainder of the page.
          */
         /* copy_from_user cannot cross TASK_SIZE ! */
         size = TASK_SIZE - (unsigned long)data;
         if (size > PAGE_SIZE)
                 size = PAGE_SIZE;
 
         i = size - exact_copy_from_user((void *)page, data, size);
         if (!i) {
                 free_page(page);
                 return -EFAULT;
         }
         if (i != PAGE_SIZE)
                 memset((char *)page + i, 0, PAGE_SIZE - i);
         *where = page;
         return 0;
 }
 
 char *copy_mount_string(const void __user *data)
 {
         return data ? strndup_user(data, PAGE_SIZE) : NULL;
 }
 
 /*
  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
  *
  * data is a (void *) that can point to any structure up to
  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
  * information (or be NULL).
  *
  * Pre-0.97 versions of mount() didn't have a flags word.
  * When the flags word was introduced its top half was required
  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
  * Therefore, if this magic number is present, it carries no information
  * and must be discarded.
  */
 long do_mount(const char *dev_name, const char __user *dir_name,
                 const char *type_page, unsigned long flags, void *data_page)
 {
         struct path path;
         int retval = 0;
         int mnt_flags = 0;
 
         /* Discard magic */
         if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
                 flags &= ~MS_MGC_MSK;
 
         /* Basic sanity checks */
         if (data_page)
                 ((char *)data_page)[PAGE_SIZE - 1] = 0;
 
         /* ... and get the mountpoint */
         retval = user_path(dir_name, &path);
         if (retval)
                 return retval;
 
         retval = security_sb_mount(dev_name, &path,
                                    type_page, flags, data_page);
         if (!retval && !may_mount())
                 retval = -EPERM;
         if (retval)
                 goto dput_out;
 
         /* Default to relatime unless overriden */
         if (!(flags & MS_NOATIME))
                 mnt_flags |= MNT_RELATIME;
 
         /* Separate the per-mountpoint flags */
         if (flags & MS_NOSUID)
                 mnt_flags |= MNT_NOSUID;
         if (flags & MS_NODEV)
                 mnt_flags |= MNT_NODEV;
         if (flags & MS_NOEXEC)
                 mnt_flags |= MNT_NOEXEC;
         if (flags & MS_NOATIME)
                 mnt_flags |= MNT_NOATIME;
         if (flags & MS_NODIRATIME)
                 mnt_flags |= MNT_NODIRATIME;
         if (flags & MS_STRICTATIME)
                 mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
         if (flags & MS_RDONLY)
                 mnt_flags |= MNT_READONLY;
 
         /* The default atime for remount is preservation */
         if ((flags & MS_REMOUNT) &&
             ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
                        MS_STRICTATIME)) == 0)) {
                 mnt_flags &= ~MNT_ATIME_MASK;
                 mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK;
         }
 
         flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
                    MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
                    MS_STRICTATIME);
 
         if (flags & MS_REMOUNT)
                 retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
                                     data_page);
         else if (flags & MS_BIND)
                 retval = do_loopback(&path, dev_name, flags & MS_REC);
         else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
                 retval = do_change_type(&path, flags);
         else if (flags & MS_MOVE)
                 retval = do_move_mount(&path, dev_name);
         else
                 retval = do_new_mount(&path, type_page, flags, mnt_flags,
                                       dev_name, data_page);
 dput_out:
         path_put(&path);
         return retval;
 }
 
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
         ns_free_inum(&ns->ns);
         put_user_ns(ns->user_ns);
         kfree(ns);
 }
 
 /*
  * Assign a sequence number so we can detect when we attempt to bind
  * mount a reference to an older mount namespace into the current
  * mount namespace, preventing reference counting loops.  A 64bit
  * number incrementing at 10Ghz will take 12,427 years to wrap which
  * is effectively never, so we can ignore the possibility.
  */
 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
 
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 {
         struct mnt_namespace *new_ns;
         int ret;
 
         new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
         if (!new_ns)
                 return ERR_PTR(-ENOMEM);
         ret = ns_alloc_inum(&new_ns->ns);
         if (ret) {
                 kfree(new_ns);
                 return ERR_PTR(ret);
         }
         new_ns->ns.ops = &mntns_operations;
         new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
         atomic_set(&new_ns->count, 1);
         new_ns->root = NULL;
         INIT_LIST_HEAD(&new_ns->list);
         init_waitqueue_head(&new_ns->poll);
         new_ns->event = 0;
         new_ns->user_ns = get_user_ns(user_ns);
         return new_ns;
 }
 
 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
                 struct user_namespace *user_ns, struct fs_struct *new_fs)
 {
         struct mnt_namespace *new_ns;
         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
         struct mount *p, *q;
         struct mount *old;
         struct mount *new;
         int copy_flags;
 
         BUG_ON(!ns);
 
         if (likely(!(flags & CLONE_NEWNS))) {
                 get_mnt_ns(ns);
                 return ns;
         }
 
         old = ns->root;
 
         new_ns = alloc_mnt_ns(user_ns);
         if (IS_ERR(new_ns))
                 return new_ns;
 
         namespace_lock();
         /* First pass: copy the tree topology */
         copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
         if (user_ns != ns->user_ns)
                 copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
         new = copy_tree(old, old->mnt.mnt_root, copy_flags);
         if (IS_ERR(new)) {
                 namespace_unlock();
                 free_mnt_ns(new_ns);
                 return ERR_CAST(new);
         }
         new_ns->root = new;
         list_add_tail(&new_ns->list, &new->mnt_list);
 
         /*
          * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
          * as belonging to new namespace.  We have already acquired a private
          * fs_struct, so tsk->fs->lock is not needed.
          */
         p = old;
         q = new;
         while (p) {
                 q->mnt_ns = new_ns;
                 if (new_fs) {
                         if (&p->mnt == new_fs->root.mnt) {
                                 new_fs->root.mnt = mntget(&q->mnt);
                                 rootmnt = &p->mnt;
                         }
                         if (&p->mnt == new_fs->pwd.mnt) {
                                 new_fs->pwd.mnt = mntget(&q->mnt);
                                 pwdmnt = &p->mnt;
                         }
                 }
                 p = next_mnt(p, old);
                 q = next_mnt(q, new);
                 if (!q)
                         break;
                 while (p->mnt.mnt_root != q->mnt.mnt_root)
                         p = next_mnt(p, old);
         }
         namespace_unlock();
 
         if (rootmnt)
                 mntput(rootmnt);
         if (pwdmnt)
                 mntput(pwdmnt);
 
         return new_ns;
 }
 
 /**
  * create_mnt_ns - creates a private namespace and adds a root filesystem
  * @mnt: pointer to the new root filesystem mountpoint
  */
 static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
 {
         struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
         if (!IS_ERR(new_ns)) {
                 struct mount *mnt = real_mount(m);
                 mnt->mnt_ns = new_ns;
                 new_ns->root = mnt;
                 list_add(&mnt->mnt_list, &new_ns->list);
         } else {
                 mntput(m);
         }
         return new_ns;
 }
 
 struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
 {
         struct mnt_namespace *ns;
         struct super_block *s;
         struct path path;
         int err;
 
         ns = create_mnt_ns(mnt);
         if (IS_ERR(ns))
                 return ERR_CAST(ns);
 
         err = vfs_path_lookup(mnt->mnt_root, mnt,
                         name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
 
         put_mnt_ns(ns);
 
         if (err)
                 return ERR_PTR(err);
 
         /* trade a vfsmount reference for active sb one */
         s = path.mnt->mnt_sb;
         atomic_inc(&s->s_active);
         mntput(path.mnt);
         /* lock the sucker */
         down_write(&s->s_umount);
         /* ... and return the root of (sub)tree on it */
         return path.dentry;
 }
 EXPORT_SYMBOL(mount_subtree);
 
 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
                 char __user *, type, unsigned long, flags, void __user *, data)
 {
         int ret;
         char *kernel_type;
         char *kernel_dev;
         unsigned long data_page;
 
         kernel_type = copy_mount_string(type);
         ret = PTR_ERR(kernel_type);
         if (IS_ERR(kernel_type))
                 goto out_type;
 
         kernel_dev = copy_mount_string(dev_name);
         ret = PTR_ERR(kernel_dev);
         if (IS_ERR(kernel_dev))
                 goto out_dev;
 
         ret = copy_mount_options(data, &data_page);
         if (ret < 0)
                 goto out_data;
 
         ret = do_mount(kernel_dev, dir_name, kernel_type, flags,
                 (void *) data_page);
 
         free_page(data_page);
 out_data:
         kfree(kernel_dev);
 out_dev:
         kfree(kernel_type);
 out_type:
         return ret;
 }
 
 /*
  * Return true if path is reachable from root
  *
  * namespace_sem or mount_lock is held
  */
 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
                          const struct path *root)
 {
         while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
                 dentry = mnt->mnt_mountpoint;
                 mnt = mnt->mnt_parent;
         }
         return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
 }
 
 int path_is_under(struct path *path1, struct path *path2)
 {
         int res;
         read_seqlock_excl(&mount_lock);
         res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
         read_sequnlock_excl(&mount_lock);
         return res;
 }
 EXPORT_SYMBOL(path_is_under);
 
 /*
  * pivot_root Semantics:
  * Moves the root file system of the current process to the directory put_old,
  * makes new_root as the new root file system of the current process, and sets
  * root/cwd of all processes which had them on the current root to new_root.
  *
  * Restrictions:
  * The new_root and put_old must be directories, and  must not be on the
  * same file  system as the current process root. The put_old  must  be
  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
  * pointed to by put_old must yield the same directory as new_root. No other
  * file system may be mounted on put_old. After all, new_root is a mountpoint.
  *
  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
  * in this situation.
  *
  * Notes:
  *  - we don't move root/cwd if they are not at the root (reason: if something
  *    cared enough to change them, it's probably wrong to force them elsewhere)
  *  - it's okay to pick a root that isn't the root of a file system, e.g.
  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
  *    first.
  */
 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                 const char __user *, put_old)
 {
         struct path new, old, parent_path, root_parent, root;
         struct mount *new_mnt, *root_mnt, *old_mnt;
         struct mountpoint *old_mp, *root_mp;
         int error;
 
         if (!may_mount())
                 return -EPERM;
 
         error = user_path_dir(new_root, &new);
         if (error)
                 goto out0;
 
         error = user_path_dir(put_old, &old);
         if (error)
                 goto out1;
 
         error = security_sb_pivotroot(&old, &new);
         if (error)
                 goto out2;
 
         get_fs_root(current->fs, &root);
         old_mp = lock_mount(&old);
         error = PTR_ERR(old_mp);
         if (IS_ERR(old_mp))
                 goto out3;
 
         error = -EINVAL;
         new_mnt = real_mount(new.mnt);
         root_mnt = real_mount(root.mnt);
         old_mnt = real_mount(old.mnt);
         if (IS_MNT_SHARED(old_mnt) ||
                 IS_MNT_SHARED(new_mnt->mnt_parent) ||
                 IS_MNT_SHARED(root_mnt->mnt_parent))
                 goto out4;
         if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
                 goto out4;
         if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
                 goto out4;
         error = -ENOENT;
         if (d_unlinked(new.dentry))
                 goto out4;
         error = -EBUSY;
         if (new_mnt == root_mnt || old_mnt == root_mnt)
                 goto out4; /* loop, on the same file system  */
         error = -EINVAL;
         if (root.mnt->mnt_root != root.dentry)
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(root_mnt))
                 goto out4; /* not attached */
         root_mp = root_mnt->mnt_mp;
         if (new.mnt->mnt_root != new.dentry)
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(new_mnt))
                 goto out4; /* not attached */
         /* make sure we can reach put_old from new_root */
         if (!is_path_reachable(old_mnt, old.dentry, &new))
                 goto out4;
         /* make certain new is below the root */
         if (!is_path_reachable(new_mnt, new.dentry, &root))
                 goto out4;
         root_mp->m_count++; /* pin it so it won't go away */
         lock_mount_hash();
         detach_mnt(new_mnt, &parent_path);
         detach_mnt(root_mnt, &root_parent);
         if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
                 new_mnt->mnt.mnt_flags |= MNT_LOCKED;
                 root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
         }
         /* mount old root on put_old */
         attach_mnt(root_mnt, old_mnt, old_mp);
         /* mount new_root on / */
         attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
         touch_mnt_namespace(current->nsproxy->mnt_ns);
         /* A moved mount should not expire automatically */
         list_del_init(&new_mnt->mnt_expire);
         unlock_mount_hash();
         chroot_fs_refs(&root, &new);
         put_mountpoint(root_mp);
         error = 0;
 out4:
         unlock_mount(old_mp);
         if (!error) {
                 path_put(&root_parent);
                 path_put(&parent_path);
         }
 out3:
         path_put(&root);
 out2:
         path_put(&old);
 out1:
         path_put(&new);
 out0:
         return error;
 }
 
 static void __init init_mount_tree(void)
 {
         struct vfsmount *mnt;
         struct mnt_namespace *ns;
         struct path root;
         struct file_system_type *type;
 
         type = get_fs_type("rootfs");
         if (!type)
                 panic("Can't find rootfs type");
         mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
         put_filesystem(type);
         if (IS_ERR(mnt))
                 panic("Can't create rootfs");
 
         ns = create_mnt_ns(mnt);
         if (IS_ERR(ns))
                 panic("Can't allocate initial namespace");
 
         init_task.nsproxy->mnt_ns = ns;
         get_mnt_ns(ns);
 
         root.mnt = mnt;
         root.dentry = mnt->mnt_root;
         mnt->mnt_flags |= MNT_LOCKED;
 
         set_fs_pwd(current->fs, &root);
         set_fs_root(current->fs, &root);
 }
 
 void __init mnt_init(void)
 {
         unsigned u;
         int err;
 
         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 
         mount_hashtable = alloc_large_system_hash("Mount-cache",
                                 sizeof(struct hlist_head),
                                 mhash_entries, 19,
                                 0,
                                 &m_hash_shift, &m_hash_mask, 0, 0);
         mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
                                 sizeof(struct hlist_head),
                                 mphash_entries, 19,
                                 0,
                                 &mp_hash_shift, &mp_hash_mask, 0, 0);
 
         if (!mount_hashtable || !mountpoint_hashtable)
                 panic("Failed to allocate mount hash table\n");
 
         for (u = 0; u <= m_hash_mask; u++)
                 INIT_HLIST_HEAD(&mount_hashtable[u]);
         for (u = 0; u <= mp_hash_mask; u++)
                 INIT_HLIST_HEAD(&mountpoint_hashtable[u]);
 
         kernfs_init();
 
         err = sysfs_init();
         if (err)
                 printk(KERN_WARNING "%s: sysfs_init error: %d\n",
                         __func__, err);
         fs_kobj = kobject_create_and_add("fs", NULL);
         if (!fs_kobj)
                 printk(KERN_WARNING "%s: kobj create error\n", __func__);
         init_rootfs();
         init_mount_tree();
 }
 
 void put_mnt_ns(struct mnt_namespace *ns)
 {
         if (!atomic_dec_and_test(&ns->count))
                 return;
         drop_collected_mounts(&ns->root->mnt);
         free_mnt_ns(ns);
 }
 
 struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
 {
         struct vfsmount *mnt;
         mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
         if (!IS_ERR(mnt)) {
                 /*
                  * it is a longterm mount, don't release mnt until
                  * we unmount before file sys is unregistered
                 */
                 real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
         }
         return mnt;
 }
 EXPORT_SYMBOL_GPL(kern_mount_data);
 
 void kern_unmount(struct vfsmount *mnt)
 {
         /* release long term mount so mount point can be released */
         if (!IS_ERR_OR_NULL(mnt)) {
                 real_mount(mnt)->mnt_ns = NULL;
                 synchronize_rcu();      /* yecchhh... */
                 mntput(mnt);
         }
 }
 EXPORT_SYMBOL(kern_unmount);
 
 bool our_mnt(struct vfsmount *mnt)
 {
         return check_mnt(real_mount(mnt));
 }
 
 bool current_chrooted(void)
 {
         /* Does the current process have a non-standard root */
         struct path ns_root;
         struct path fs_root;
         bool chrooted;
 
         /* Find the namespace root */
         ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
         ns_root.dentry = ns_root.mnt->mnt_root;
         path_get(&ns_root);
         while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
                 ;
 
         get_fs_root(current->fs, &fs_root);
 
         chrooted = !path_equal(&fs_root, &ns_root);
 
         path_put(&fs_root);
         path_put(&ns_root);
 
         return chrooted;
 }
 
 static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
 {
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         int new_flags = *new_mnt_flags;
         struct mount *mnt;
         bool visible = false;
 
         if (unlikely(!ns))
                 return false;
 
         down_read(&namespace_sem);
         list_for_each_entry(mnt, &ns->list, mnt_list) {
                 struct mount *child;
                 if (mnt->mnt.mnt_sb->s_type != type)
                         continue;
 
                 /* This mount is not fully visible if it's root directory
                  * is not the root directory of the filesystem.
                  */
                 if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
                         continue;
 
                 /* Verify the mount flags are equal to or more permissive
                  * than the proposed new mount.
                  */
                 if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
                     !(new_flags & MNT_READONLY))
                         continue;
                 if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
                     !(new_flags & MNT_NODEV))
                         continue;
                 if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
                     ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
                         continue;
 
                 /* This mount is not fully visible if there are any
                  * locked child mounts that cover anything except for
                  * empty directories.
                  */
                 list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
                         struct inode *inode = child->mnt_mountpoint->d_inode;
                         /* Only worry about locked mounts */
                         if (!(mnt->mnt.mnt_flags & MNT_LOCKED))
                                 continue;
                         /* Is the directory permanetly empty? */
                         if (!is_empty_dir_inode(inode))
                                 goto next;
                 }
                 /* Preserve the locked attributes */
                 *new_mnt_flags |= mnt->mnt.mnt_flags & (MNT_LOCK_READONLY | \
                                                         MNT_LOCK_NODEV    | \
                                                         MNT_LOCK_ATIME);
                 visible = true;
                 goto found;
         next:   ;
         }
 found:
         up_read(&namespace_sem);
         return visible;
 }
 
 static struct ns_common *mntns_get(struct task_struct *task)
 {
         struct ns_common *ns = NULL;
         struct nsproxy *nsproxy;
 
         task_lock(task);
         nsproxy = task->nsproxy;
         if (nsproxy) {
                 ns = &nsproxy->mnt_ns->ns;
                 get_mnt_ns(to_mnt_ns(ns));
         }
         task_unlock(task);
 
         return ns;
 }
 
 static void mntns_put(struct ns_common *ns)
 {
         put_mnt_ns(to_mnt_ns(ns));
 }
 
 static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
         struct fs_struct *fs = current->fs;
         struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
         struct path root;
 
         if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
             !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
                 return -EPERM;
 
         if (fs->users != 1)
                 return -EINVAL;
 
         get_mnt_ns(mnt_ns);
         put_mnt_ns(nsproxy->mnt_ns);
         nsproxy->mnt_ns = mnt_ns;
 
         /* Find the root */
         root.mnt    = &mnt_ns->root->mnt;
         root.dentry = mnt_ns->root->mnt.mnt_root;
         path_get(&root);
         while(d_mountpoint(root.dentry) && follow_down_one(&root))
                 ;
 
         /* Update the pwd and root */
         set_fs_pwd(fs, &root);
         set_fs_root(fs, &root);
 
         path_put(&root);
         return 0;
 }
 
 const struct proc_ns_operations mntns_operations = {
         .name           = "mnt",
         .type           = CLONE_NEWNS,
         .get            = mntns_get,
         .put            = mntns_put,
         .install        = mntns_install,
 };
 

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