fs/ecryptfs/kthread.c

   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;
 106
 107         mutex_lock(&ecryptfs_kthread_ctl.mux);
 108         ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
 109         list_for_each_entry(req, &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 }