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 <linux/file.h>
  29 #include "ecryptfs_kernel.h"
  30
  31 struct ecryptfs_open_req {
  32         struct file **lower_file;
  33         struct path path;
  34         struct completion done;
  35         struct list_head kthread_ctl_list;
  36 };
  37
  38 static struct ecryptfs_kthread_ctl {
  39 #define ECRYPTFS_KTHREAD_ZOMBIE 0x00000001
  40         u32 flags;
  41         struct mutex mux;
  42         struct list_head req_list;
  43         wait_queue_head_t wait;
  44 } ecryptfs_kthread_ctl;
  45
  46 static struct task_struct *ecryptfs_kthread;
  47
  48 /**
  49  * ecryptfs_threadfn
  50  * @ignored: ignored
  51  *
  52  * The eCryptfs kernel thread that has the responsibility of getting
  53  * the lower file with RW permissions.
  54  *
  55  * Returns zero on success; non-zero otherwise
  56  */
  57 static int ecryptfs_threadfn(void *ignored)
  58 {
  59         set_freezable();
  60         while (1)  {
  61                 struct ecryptfs_open_req *req;
  62
  63                 wait_event_freezable(
  64                         ecryptfs_kthread_ctl.wait,
  65                         (!list_empty(&ecryptfs_kthread_ctl.req_list)
  66                          || kthread_should_stop()));
  67                 mutex_lock(&ecryptfs_kthread_ctl.mux);
  68                 if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
  69                         mutex_unlock(&ecryptfs_kthread_ctl.mux);
  70                         goto out;
  71                 }
  72                 while (!list_empty(&ecryptfs_kthread_ctl.req_list)) {
  73                         req = list_first_entry(&ecryptfs_kthread_ctl.req_list,
  74                                                struct ecryptfs_open_req,
  75                                                kthread_ctl_list);
  76                         list_del(&req->kthread_ctl_list);
  77                         *req->lower_file = dentry_open(&req->path,
  78                                 (O_RDWR | O_LARGEFILE), current_cred());
  79                         complete(&req->done);
  80                 }
  81                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
  82         }
  83 out:
  84         return 0;
  85 }
  86
  87 int __init ecryptfs_init_kthread(void)
  88 {
  89         int rc = 0;
  90
  91         mutex_init(&ecryptfs_kthread_ctl.mux);
  92         init_waitqueue_head(&ecryptfs_kthread_ctl.wait);
  93         INIT_LIST_HEAD(&ecryptfs_kthread_ctl.req_list);
  94         ecryptfs_kthread = kthread_run(&ecryptfs_threadfn, NULL,
  95                                        "ecryptfs-kthread");
  96         if (IS_ERR(ecryptfs_kthread)) {
  97                 rc = PTR_ERR(ecryptfs_kthread);
  98                 printk(KERN_ERR "%s: Failed to create kernel thread; rc = [%d]"
  99                        "\n", __func__, rc);
 100         }
 101         return rc;
 102 }
 103
 104 void ecryptfs_destroy_kthread(void)
 105 {
 106         struct ecryptfs_open_req *req, *tmp;
 107
 108         mutex_lock(&ecryptfs_kthread_ctl.mux);
 109         ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
 110         list_for_each_entry_safe(req, tmp, &ecryptfs_kthread_ctl.req_list,
 111                                  kthread_ctl_list) {
 112                 list_del(&req->kthread_ctl_list);
 113                 *req->lower_file = ERR_PTR(-EIO);
 114                 complete(&req->done);
 115         }
 116         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 117         kthread_stop(ecryptfs_kthread);
 118         wake_up(&ecryptfs_kthread_ctl.wait);
 119 }
 120
 121 /**
 122  * ecryptfs_privileged_open
 123  * @lower_file: Result of dentry_open by root on lower dentry
 124  * @lower_dentry: Lower dentry for file to open
 125  * @lower_mnt: Lower vfsmount for file to open
 126  *
 127  * This function gets a r/w file opened againt the lower dentry.
 128  *
 129  * Returns zero on success; non-zero otherwise
 130  */
 131 int ecryptfs_privileged_open(struct file **lower_file,
 132                              struct dentry *lower_dentry,
 133                              struct vfsmount *lower_mnt,
 134                              const struct cred *cred)
 135 {
 136         struct ecryptfs_open_req req;
 137         int flags = O_LARGEFILE;
 138         int rc = 0;
 139
 140         init_completion(&req.done);
 141         req.lower_file = lower_file;
 142         req.path.dentry = lower_dentry;
 143         req.path.mnt = lower_mnt;
 144
 145         /* Corresponding dput() and mntput() are done when the
 146          * lower file is fput() when all eCryptfs files for the inode are
 147          * released. */
 148         flags |= IS_RDONLY(d_inode(lower_dentry)) ? O_RDONLY : O_RDWR;
 149         (*lower_file) = dentry_open(&req.path, flags, cred);
 150         if (!IS_ERR(*lower_file))
 151                 goto have_file;
 152         if ((flags & O_ACCMODE) == O_RDONLY) {
 153                 rc = PTR_ERR((*lower_file));
 154                 goto out;
 155         }
 156         mutex_lock(&ecryptfs_kthread_ctl.mux);
 157         if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
 158                 rc = -EIO;
 159                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
 160                 printk(KERN_ERR "%s: We are in the middle of shutting down; "
 161                        "aborting privileged request to open lower file\n",
 162                         __func__);
 163                 goto out;
 164         }
 165         list_add_tail(&req.kthread_ctl_list, &ecryptfs_kthread_ctl.req_list);
 166         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 167         wake_up(&ecryptfs_kthread_ctl.wait);
 168         wait_for_completion(&req.done);
 169         if (IS_ERR(*lower_file)) {
 170                 rc = PTR_ERR(*lower_file);
 171                 goto out;
 172         }
 173 have_file:
 174         if ((*lower_file)->f_op->mmap == NULL) {
 175                 fput(*lower_file);
 176                 *lower_file = NULL;
 177                 rc = -EMEDIUMTYPE;
 178         }
 179 out:
 180         return rc;
 181 }