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Linux/fs/ecryptfs/kthread.c

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  1 /**
  2  * eCryptfs: Linux filesystem encryption layer
  3  *
  4  * Copyright (C) 2008 International Business Machines Corp.
  5  *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
  6  *
  7  * This program is free software; you can redistribute it and/or
  8  * modify it under the terms of the GNU General Public License as
  9  * published by the Free Software Foundation; either version 2 of the
 10  * License, or (at your option) any later version.
 11  *
 12  * This program is distributed in the hope that it will be useful, but
 13  * WITHOUT ANY WARRANTY; without even the implied warranty of
 14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 15  * General Public License for more details.
 16  *
 17  * You should have received a copy of the GNU General Public License
 18  * along with this program; if not, write to the Free Software
 19  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 20  * 02111-1307, USA.
 21  */
 22 
 23 #include <linux/kthread.h>
 24 #include <linux/freezer.h>
 25 #include <linux/slab.h>
 26 #include <linux/wait.h>
 27 #include <linux/mount.h>
 28 #include "ecryptfs_kernel.h"
 29 
 30 struct ecryptfs_open_req {
 31         struct file **lower_file;
 32         struct path path;
 33         struct completion done;
 34         struct list_head kthread_ctl_list;
 35 };
 36 
 37 static struct ecryptfs_kthread_ctl {
 38 #define ECRYPTFS_KTHREAD_ZOMBIE 0x00000001
 39         u32 flags;
 40         struct mutex mux;
 41         struct list_head req_list;
 42         wait_queue_head_t wait;
 43 } ecryptfs_kthread_ctl;
 44 
 45 static struct task_struct *ecryptfs_kthread;
 46 
 47 /**
 48  * ecryptfs_threadfn
 49  * @ignored: ignored
 50  *
 51  * The eCryptfs kernel thread that has the responsibility of getting
 52  * the lower file with RW permissions.
 53  *
 54  * Returns zero on success; non-zero otherwise
 55  */
 56 static int ecryptfs_threadfn(void *ignored)
 57 {
 58         set_freezable();
 59         while (1)  {
 60                 struct ecryptfs_open_req *req;
 61 
 62                 wait_event_freezable(
 63                         ecryptfs_kthread_ctl.wait,
 64                         (!list_empty(&ecryptfs_kthread_ctl.req_list)
 65                          || kthread_should_stop()));
 66                 mutex_lock(&ecryptfs_kthread_ctl.mux);
 67                 if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
 68                         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 69                         goto out;
 70                 }
 71                 while (!list_empty(&ecryptfs_kthread_ctl.req_list)) {
 72                         req = list_first_entry(&ecryptfs_kthread_ctl.req_list,
 73                                                struct ecryptfs_open_req,
 74                                                kthread_ctl_list);
 75                         list_del(&req->kthread_ctl_list);
 76                         *req->lower_file = dentry_open(&req->path,
 77                                 (O_RDWR | O_LARGEFILE), current_cred());
 78                         complete(&req->done);
 79                 }
 80                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
 81         }
 82 out:
 83         return 0;
 84 }
 85 
 86 int __init ecryptfs_init_kthread(void)
 87 {
 88         int rc = 0;
 89 
 90         mutex_init(&ecryptfs_kthread_ctl.mux);
 91         init_waitqueue_head(&ecryptfs_kthread_ctl.wait);
 92         INIT_LIST_HEAD(&ecryptfs_kthread_ctl.req_list);
 93         ecryptfs_kthread = kthread_run(&ecryptfs_threadfn, NULL,
 94                                        "ecryptfs-kthread");
 95         if (IS_ERR(ecryptfs_kthread)) {
 96                 rc = PTR_ERR(ecryptfs_kthread);
 97                 printk(KERN_ERR "%s: Failed to create kernel thread; rc = [%d]"
 98                        "\n", __func__, rc);
 99         }
100         return rc;
101 }
102 
103 void ecryptfs_destroy_kthread(void)
104 {
105         struct ecryptfs_open_req *req, *tmp;
106 
107         mutex_lock(&ecryptfs_kthread_ctl.mux);
108         ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
109         list_for_each_entry_safe(req, tmp, &ecryptfs_kthread_ctl.req_list,
110                                  kthread_ctl_list) {
111                 list_del(&req->kthread_ctl_list);
112                 *req->lower_file = ERR_PTR(-EIO);
113                 complete(&req->done);
114         }
115         mutex_unlock(&ecryptfs_kthread_ctl.mux);
116         kthread_stop(ecryptfs_kthread);
117         wake_up(&ecryptfs_kthread_ctl.wait);
118 }
119 
120 /**
121  * ecryptfs_privileged_open
122  * @lower_file: Result of dentry_open by root on lower dentry
123  * @lower_dentry: Lower dentry for file to open
124  * @lower_mnt: Lower vfsmount for file to open
125  *
126  * This function gets a r/w file opened againt the lower dentry.
127  *
128  * Returns zero on success; non-zero otherwise
129  */
130 int ecryptfs_privileged_open(struct file **lower_file,
131                              struct dentry *lower_dentry,
132                              struct vfsmount *lower_mnt,
133                              const struct cred *cred)
134 {
135         struct ecryptfs_open_req req;
136         int flags = O_LARGEFILE;
137         int rc = 0;
138 
139         init_completion(&req.done);
140         req.lower_file = lower_file;
141         req.path.dentry = lower_dentry;
142         req.path.mnt = lower_mnt;
143 
144         /* Corresponding dput() and mntput() are done when the
145          * lower file is fput() when all eCryptfs files for the inode are
146          * released. */
147         flags |= IS_RDONLY(lower_dentry->d_inode) ? O_RDONLY : O_RDWR;
148         (*lower_file) = dentry_open(&req.path, flags, cred);
149         if (!IS_ERR(*lower_file))
150                 goto out;
151         if ((flags & O_ACCMODE) == O_RDONLY) {
152                 rc = PTR_ERR((*lower_file));
153                 goto out;
154         }
155         mutex_lock(&ecryptfs_kthread_ctl.mux);
156         if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
157                 rc = -EIO;
158                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
159                 printk(KERN_ERR "%s: We are in the middle of shutting down; "
160                        "aborting privileged request to open lower file\n",
161                         __func__);
162                 goto out;
163         }
164         list_add_tail(&req.kthread_ctl_list, &ecryptfs_kthread_ctl.req_list);
165         mutex_unlock(&ecryptfs_kthread_ctl.mux);
166         wake_up(&ecryptfs_kthread_ctl.wait);
167         wait_for_completion(&req.done);
168         if (IS_ERR(*lower_file))
169                 rc = PTR_ERR(*lower_file);
170 out:
171         return rc;
172 }
173 

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