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Linux/fs/fhandle.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 #include <linux/syscalls.h>
  3 #include <linux/slab.h>
  4 #include <linux/fs.h>
  5 #include <linux/file.h>
  6 #include <linux/mount.h>
  7 #include <linux/namei.h>
  8 #include <linux/exportfs.h>
  9 #include <linux/fs_struct.h>
 10 #include <linux/fsnotify.h>
 11 #include <linux/personality.h>
 12 #include <linux/uaccess.h>
 13 #include <linux/compat.h>
 14 #include "internal.h"
 15 #include "mount.h"
 16 
 17 static long do_sys_name_to_handle(struct path *path,
 18                                   struct file_handle __user *ufh,
 19                                   int __user *mnt_id)
 20 {
 21         long retval;
 22         struct file_handle f_handle;
 23         int handle_dwords, handle_bytes;
 24         struct file_handle *handle = NULL;
 25 
 26         /*
 27          * We need to make sure whether the file system
 28          * support decoding of the file handle
 29          */
 30         if (!path->dentry->d_sb->s_export_op ||
 31             !path->dentry->d_sb->s_export_op->fh_to_dentry)
 32                 return -EOPNOTSUPP;
 33 
 34         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
 35                 return -EFAULT;
 36 
 37         if (f_handle.handle_bytes > MAX_HANDLE_SZ)
 38                 return -EINVAL;
 39 
 40         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 41                          GFP_KERNEL);
 42         if (!handle)
 43                 return -ENOMEM;
 44 
 45         /* convert handle size to multiple of sizeof(u32) */
 46         handle_dwords = f_handle.handle_bytes >> 2;
 47 
 48         /* we ask for a non connected handle */
 49         retval = exportfs_encode_fh(path->dentry,
 50                                     (struct fid *)handle->f_handle,
 51                                     &handle_dwords,  0);
 52         handle->handle_type = retval;
 53         /* convert handle size to bytes */
 54         handle_bytes = handle_dwords * sizeof(u32);
 55         handle->handle_bytes = handle_bytes;
 56         if ((handle->handle_bytes > f_handle.handle_bytes) ||
 57             (retval == FILEID_INVALID) || (retval == -ENOSPC)) {
 58                 /* As per old exportfs_encode_fh documentation
 59                  * we could return ENOSPC to indicate overflow
 60                  * But file system returned 255 always. So handle
 61                  * both the values
 62                  */
 63                 /*
 64                  * set the handle size to zero so we copy only
 65                  * non variable part of the file_handle
 66                  */
 67                 handle_bytes = 0;
 68                 retval = -EOVERFLOW;
 69         } else
 70                 retval = 0;
 71         /* copy the mount id */
 72         if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
 73             copy_to_user(ufh, handle,
 74                          sizeof(struct file_handle) + handle_bytes))
 75                 retval = -EFAULT;
 76         kfree(handle);
 77         return retval;
 78 }
 79 
 80 /**
 81  * sys_name_to_handle_at: convert name to handle
 82  * @dfd: directory relative to which name is interpreted if not absolute
 83  * @name: name that should be converted to handle.
 84  * @handle: resulting file handle
 85  * @mnt_id: mount id of the file system containing the file
 86  * @flag: flag value to indicate whether to follow symlink or not
 87  *
 88  * @handle->handle_size indicate the space available to store the
 89  * variable part of the file handle in bytes. If there is not
 90  * enough space, the field is updated to return the minimum
 91  * value required.
 92  */
 93 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
 94                 struct file_handle __user *, handle, int __user *, mnt_id,
 95                 int, flag)
 96 {
 97         struct path path;
 98         int lookup_flags;
 99         int err;
100 
101         if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
102                 return -EINVAL;
103 
104         lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
105         if (flag & AT_EMPTY_PATH)
106                 lookup_flags |= LOOKUP_EMPTY;
107         err = user_path_at(dfd, name, lookup_flags, &path);
108         if (!err) {
109                 err = do_sys_name_to_handle(&path, handle, mnt_id);
110                 path_put(&path);
111         }
112         return err;
113 }
114 
115 static struct vfsmount *get_vfsmount_from_fd(int fd)
116 {
117         struct vfsmount *mnt;
118 
119         if (fd == AT_FDCWD) {
120                 struct fs_struct *fs = current->fs;
121                 spin_lock(&fs->lock);
122                 mnt = mntget(fs->pwd.mnt);
123                 spin_unlock(&fs->lock);
124         } else {
125                 struct fd f = fdget(fd);
126                 if (!f.file)
127                         return ERR_PTR(-EBADF);
128                 mnt = mntget(f.file->f_path.mnt);
129                 fdput(f);
130         }
131         return mnt;
132 }
133 
134 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
135 {
136         return 1;
137 }
138 
139 static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
140                              struct path *path)
141 {
142         int retval = 0;
143         int handle_dwords;
144 
145         path->mnt = get_vfsmount_from_fd(mountdirfd);
146         if (IS_ERR(path->mnt)) {
147                 retval = PTR_ERR(path->mnt);
148                 goto out_err;
149         }
150         /* change the handle size to multiple of sizeof(u32) */
151         handle_dwords = handle->handle_bytes >> 2;
152         path->dentry = exportfs_decode_fh(path->mnt,
153                                           (struct fid *)handle->f_handle,
154                                           handle_dwords, handle->handle_type,
155                                           vfs_dentry_acceptable, NULL);
156         if (IS_ERR(path->dentry)) {
157                 retval = PTR_ERR(path->dentry);
158                 goto out_mnt;
159         }
160         return 0;
161 out_mnt:
162         mntput(path->mnt);
163 out_err:
164         return retval;
165 }
166 
167 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
168                    struct path *path)
169 {
170         int retval = 0;
171         struct file_handle f_handle;
172         struct file_handle *handle = NULL;
173 
174         /*
175          * With handle we don't look at the execute bit on the
176          * the directory. Ideally we would like CAP_DAC_SEARCH.
177          * But we don't have that
178          */
179         if (!capable(CAP_DAC_READ_SEARCH)) {
180                 retval = -EPERM;
181                 goto out_err;
182         }
183         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
184                 retval = -EFAULT;
185                 goto out_err;
186         }
187         if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
188             (f_handle.handle_bytes == 0)) {
189                 retval = -EINVAL;
190                 goto out_err;
191         }
192         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
193                          GFP_KERNEL);
194         if (!handle) {
195                 retval = -ENOMEM;
196                 goto out_err;
197         }
198         /* copy the full handle */
199         *handle = f_handle;
200         if (copy_from_user(&handle->f_handle,
201                            &ufh->f_handle,
202                            f_handle.handle_bytes)) {
203                 retval = -EFAULT;
204                 goto out_handle;
205         }
206 
207         retval = do_handle_to_path(mountdirfd, handle, path);
208 
209 out_handle:
210         kfree(handle);
211 out_err:
212         return retval;
213 }
214 
215 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
216                            int open_flag)
217 {
218         long retval = 0;
219         struct path path;
220         struct file *file;
221         int fd;
222 
223         retval = handle_to_path(mountdirfd, ufh, &path);
224         if (retval)
225                 return retval;
226 
227         fd = get_unused_fd_flags(open_flag);
228         if (fd < 0) {
229                 path_put(&path);
230                 return fd;
231         }
232         file = file_open_root(path.dentry, path.mnt, "", open_flag, 0);
233         if (IS_ERR(file)) {
234                 put_unused_fd(fd);
235                 retval =  PTR_ERR(file);
236         } else {
237                 retval = fd;
238                 fsnotify_open(file);
239                 fd_install(fd, file);
240         }
241         path_put(&path);
242         return retval;
243 }
244 
245 /**
246  * sys_open_by_handle_at: Open the file handle
247  * @mountdirfd: directory file descriptor
248  * @handle: file handle to be opened
249  * @flag: open flags.
250  *
251  * @mountdirfd indicate the directory file descriptor
252  * of the mount point. file handle is decoded relative
253  * to the vfsmount pointed by the @mountdirfd. @flags
254  * value is same as the open(2) flags.
255  */
256 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
257                 struct file_handle __user *, handle,
258                 int, flags)
259 {
260         long ret;
261 
262         if (force_o_largefile())
263                 flags |= O_LARGEFILE;
264 
265         ret = do_handle_open(mountdirfd, handle, flags);
266         return ret;
267 }
268 
269 #ifdef CONFIG_COMPAT
270 /*
271  * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
272  * doesn't set the O_LARGEFILE flag.
273  */
274 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
275                              struct file_handle __user *, handle, int, flags)
276 {
277         return do_handle_open(mountdirfd, handle, flags);
278 }
279 #endif
280 

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