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 kmem_cache *ecryptfs_open_req_cache;
  31
  32 static struct ecryptfs_kthread_ctl {
  33 #define ECRYPTFS_KTHREAD_ZOMBIE 0x00000001
  34         u32 flags;
  35         struct mutex mux;
  36         struct list_head req_list;
  37         wait_queue_head_t wait;
  38 } ecryptfs_kthread_ctl;
  39
  40 static struct task_struct *ecryptfs_kthread;
  41
  42 /**
  43  * ecryptfs_threadfn
  44  * @ignored: ignored
  45  *
  46  * The eCryptfs kernel thread that has the responsibility of getting
  47  * the lower persistent file with RW permissions.
  48  *
  49  * Returns zero on success; non-zero otherwise
  50  */
  51 static int ecryptfs_threadfn(void *ignored)
  52 {
  53         set_freezable();
  54         while (1)  {
  55                 struct ecryptfs_open_req *req;
  56
  57                 wait_event_freezable(
  58                         ecryptfs_kthread_ctl.wait,
  59                         (!list_empty(&ecryptfs_kthread_ctl.req_list)
  60                          || kthread_should_stop()));
  61                 mutex_lock(&ecryptfs_kthread_ctl.mux);
  62                 if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
  63                         mutex_unlock(&ecryptfs_kthread_ctl.mux);
  64                         goto out;
  65                 }
  66                 while (!list_empty(&ecryptfs_kthread_ctl.req_list)) {
  67                         req = list_first_entry(&ecryptfs_kthread_ctl.req_list,
  68                                                struct ecryptfs_open_req,
  69                                                kthread_ctl_list);
  70                         mutex_lock(&req->mux);
  71                         list_del(&req->kthread_ctl_list);
  72                         if (!(req->flags & ECRYPTFS_REQ_ZOMBIE)) {
  73                                 dget(req->lower_dentry);
  74                                 mntget(req->lower_mnt);
  75                                 (*req->lower_file) = dentry_open(
  76                                         req->lower_dentry, req->lower_mnt,
  77                                         (O_RDWR | O_LARGEFILE), current_cred());
  78                                 req->flags |= ECRYPTFS_REQ_PROCESSED;
  79                         }
  80                         wake_up(&req->wait);
  81                         mutex_unlock(&req->mux);
  82                 }
  83                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
  84         }
  85 out:
  86         return 0;
  87 }
  88
  89 int __init ecryptfs_init_kthread(void)
  90 {
  91         int rc = 0;
  92
  93         mutex_init(&ecryptfs_kthread_ctl.mux);
  94         init_waitqueue_head(&ecryptfs_kthread_ctl.wait);
  95         INIT_LIST_HEAD(&ecryptfs_kthread_ctl.req_list);
  96         ecryptfs_kthread = kthread_run(&ecryptfs_threadfn, NULL,
  97                                        "ecryptfs-kthread");
  98         if (IS_ERR(ecryptfs_kthread)) {
  99                 rc = PTR_ERR(ecryptfs_kthread);
 100                 printk(KERN_ERR "%s: Failed to create kernel thread; rc = [%d]"
 101                        "\n", __func__, rc);
 102         }
 103         return rc;
 104 }
 105
 106 void ecryptfs_destroy_kthread(void)
 107 {
 108         struct ecryptfs_open_req *req;
 109
 110         mutex_lock(&ecryptfs_kthread_ctl.mux);
 111         ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
 112         list_for_each_entry(req, &ecryptfs_kthread_ctl.req_list,
 113                             kthread_ctl_list) {
 114                 mutex_lock(&req->mux);
 115                 req->flags |= ECRYPTFS_REQ_ZOMBIE;
 116                 wake_up(&req->wait);
 117                 mutex_unlock(&req->mux);
 118         }
 119         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 120         kthread_stop(ecryptfs_kthread);
 121         wake_up(&ecryptfs_kthread_ctl.wait);
 122 }
 123
 124 /**
 125  * ecryptfs_privileged_open
 126  * @lower_file: Result of dentry_open by root on lower dentry
 127  * @lower_dentry: Lower dentry for file to open
 128  * @lower_mnt: Lower vfsmount for file to open
 129  *
 130  * This function gets a r/w file opened againt the lower dentry.
 131  *
 132  * Returns zero on success; non-zero otherwise
 133  */
 134 int ecryptfs_privileged_open(struct file **lower_file,
 135                              struct dentry *lower_dentry,
 136                              struct vfsmount *lower_mnt,
 137                              const struct cred *cred)
 138 {
 139         struct ecryptfs_open_req *req;
 140         int flags = O_LARGEFILE;
 141         int rc = 0;
 142
 143         /* Corresponding dput() and mntput() are done when the
 144          * persistent file is fput() when the eCryptfs inode is
 145          * destroyed. */
 146         dget(lower_dentry);
 147         mntget(lower_mnt);
 148         flags |= IS_RDONLY(lower_dentry->d_inode) ? O_RDONLY : O_RDWR;
 149         (*lower_file) = dentry_open(lower_dentry, lower_mnt, flags, cred);
 150         if (!IS_ERR(*lower_file))
 151                 goto out;
 152         if (flags & O_RDONLY) {
 153                 rc = PTR_ERR((*lower_file));
 154                 goto out;
 155         }
 156         req = kmem_cache_alloc(ecryptfs_open_req_cache, GFP_KERNEL);
 157         if (!req) {
 158                 rc = -ENOMEM;
 159                 goto out;
 160         }
 161         mutex_init(&req->mux);
 162         req->lower_file = lower_file;
 163         req->lower_dentry = lower_dentry;
 164         req->lower_mnt = lower_mnt;
 165         init_waitqueue_head(&req->wait);
 166         req->flags = 0;
 167         mutex_lock(&ecryptfs_kthread_ctl.mux);
 168         if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
 169                 rc = -EIO;
 170                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
 171                 printk(KERN_ERR "%s: We are in the middle of shutting down; "
 172                        "aborting privileged request to open lower file\n",
 173                         __func__);
 174                 goto out_free;
 175         }
 176         list_add_tail(&req->kthread_ctl_list, &ecryptfs_kthread_ctl.req_list);
 177         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 178         wake_up(&ecryptfs_kthread_ctl.wait);
 179         wait_event(req->wait, (req->flags != 0));
 180         mutex_lock(&req->mux);
 181         BUG_ON(req->flags == 0);
 182         if (req->flags & ECRYPTFS_REQ_DROPPED
 183             || req->flags & ECRYPTFS_REQ_ZOMBIE) {
 184                 rc = -EIO;
 185                 printk(KERN_WARNING "%s: Privileged open request dropped\n",
 186                        __func__);
 187                 goto out_unlock;
 188         }
 189         if (IS_ERR(*req->lower_file))
 190                 rc = PTR_ERR(*req->lower_file);
 191 out_unlock:
 192         mutex_unlock(&req->mux);
 193 out_free:
 194         kmem_cache_free(ecryptfs_open_req_cache, req);
 195 out:
 196         return rc;
 197 }