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/wait.h>
  26 #include <linux/mount.h>
  27 #include "ecryptfs_kernel.h"
  28
  29 struct kmem_cache *ecryptfs_open_req_cache;
  30
  31 static struct ecryptfs_kthread_ctl {
  32 #define ECRYPTFS_KTHREAD_ZOMBIE 0x00000001
  33         u32 flags;
  34         struct mutex mux;
  35         struct list_head req_list;
  36         wait_queue_head_t wait;
  37 } ecryptfs_kthread_ctl;
  38
  39 static struct task_struct *ecryptfs_kthread;
  40
  41 /**
  42  * ecryptfs_threadfn
  43  * @ignored: ignored
  44  *
  45  * The eCryptfs kernel thread that has the responsibility of getting
  46  * the lower persistent file with RW permissions.
  47  *
  48  * Returns zero on success; non-zero otherwise
  49  */
  50 static int ecryptfs_threadfn(void *ignored)
  51 {
  52         set_freezable();
  53         while (1)  {
  54                 struct ecryptfs_open_req *req;
  55
  56                 wait_event_freezable(
  57                         ecryptfs_kthread_ctl.wait,
  58                         (!list_empty(&ecryptfs_kthread_ctl.req_list)
  59                          || kthread_should_stop()));
  60                 mutex_lock(&ecryptfs_kthread_ctl.mux);
  61                 if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
  62                         mutex_unlock(&ecryptfs_kthread_ctl.mux);
  63                         goto out;
  64                 }
  65                 while (!list_empty(&ecryptfs_kthread_ctl.req_list)) {
  66                         req = list_first_entry(&ecryptfs_kthread_ctl.req_list,
  67                                                struct ecryptfs_open_req,
  68                                                kthread_ctl_list);
  69                         mutex_lock(&req->mux);
  70                         list_del(&req->kthread_ctl_list);
  71                         if (!(req->flags & ECRYPTFS_REQ_ZOMBIE)) {
  72                                 dget(req->lower_dentry);
  73                                 mntget(req->lower_mnt);
  74                                 (*req->lower_file) = dentry_open(
  75                                         req->lower_dentry, req->lower_mnt,
  76                                         (O_RDWR | O_LARGEFILE));
  77                                 req->flags |= ECRYPTFS_REQ_PROCESSED;
  78                         }
  79                         wake_up(&req->wait);
  80                         mutex_unlock(&req->mux);
  81                 }
  82                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
  83         }
  84 out:
  85         return 0;
  86 }
  87
  88 int ecryptfs_init_kthread(void)
  89 {
  90         int rc = 0;
  91
  92         mutex_init(&ecryptfs_kthread_ctl.mux);
  93         init_waitqueue_head(&ecryptfs_kthread_ctl.wait);
  94         INIT_LIST_HEAD(&ecryptfs_kthread_ctl.req_list);
  95         ecryptfs_kthread = kthread_run(&ecryptfs_threadfn, NULL,
  96                                        "ecryptfs-kthread");
  97         if (IS_ERR(ecryptfs_kthread)) {
  98                 rc = PTR_ERR(ecryptfs_kthread);
  99                 printk(KERN_ERR "%s: Failed to create kernel thread; rc = [%d]"
 100                        "\n", __func__, rc);
 101         }
 102         return rc;
 103 }
 104
 105 void ecryptfs_destroy_kthread(void)
 106 {
 107         struct ecryptfs_open_req *req;
 108
 109         mutex_lock(&ecryptfs_kthread_ctl.mux);
 110         ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
 111         list_for_each_entry(req, &ecryptfs_kthread_ctl.req_list,
 112                             kthread_ctl_list) {
 113                 mutex_lock(&req->mux);
 114                 req->flags |= ECRYPTFS_REQ_ZOMBIE;
 115                 wake_up(&req->wait);
 116                 mutex_unlock(&req->mux);
 117         }
 118         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 119         kthread_stop(ecryptfs_kthread);
 120         wake_up(&ecryptfs_kthread_ctl.wait);
 121 }
 122
 123 /**
 124  * ecryptfs_privileged_open
 125  * @lower_file: Result of dentry_open by root on lower dentry
 126  * @lower_dentry: Lower dentry for file to open
 127  * @lower_mnt: Lower vfsmount for file to open
 128  *
 129  * This function gets a r/w file opened againt the lower dentry.
 130  *
 131  * Returns zero on success; non-zero otherwise
 132  */
 133 int ecryptfs_privileged_open(struct file **lower_file,
 134                              struct dentry *lower_dentry,
 135                              struct vfsmount *lower_mnt)
 136 {
 137         struct ecryptfs_open_req *req;
 138         int rc = 0;
 139
 140         /* Corresponding dput() and mntput() are done when the
 141          * persistent file is fput() when the eCryptfs inode is
 142          * destroyed. */
 143         dget(lower_dentry);
 144         mntget(lower_mnt);
 145         (*lower_file) = dentry_open(lower_dentry, lower_mnt,
 146                                     (O_RDWR | O_LARGEFILE));
 147         if (!IS_ERR(*lower_file))
 148                 goto out;
 149         req = kmem_cache_alloc(ecryptfs_open_req_cache, GFP_KERNEL);
 150         if (!req) {
 151                 rc = -ENOMEM;
 152                 goto out;
 153         }
 154         mutex_init(&req->mux);
 155         req->lower_file = lower_file;
 156         req->lower_dentry = lower_dentry;
 157         req->lower_mnt = lower_mnt;
 158         init_waitqueue_head(&req->wait);
 159         req->flags = 0;
 160         mutex_lock(&ecryptfs_kthread_ctl.mux);
 161         if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
 162                 rc = -EIO;
 163                 mutex_unlock(&ecryptfs_kthread_ctl.mux);
 164                 printk(KERN_ERR "%s: We are in the middle of shutting down; "
 165                        "aborting privileged request to open lower file\n",
 166                         __func__);
 167                 goto out_free;
 168         }
 169         list_add_tail(&req->kthread_ctl_list, &ecryptfs_kthread_ctl.req_list);
 170         mutex_unlock(&ecryptfs_kthread_ctl.mux);
 171         wake_up(&ecryptfs_kthread_ctl.wait);
 172         wait_event(req->wait, (req->flags != 0));
 173         mutex_lock(&req->mux);
 174         BUG_ON(req->flags == 0);
 175         if (req->flags & ECRYPTFS_REQ_DROPPED
 176             || req->flags & ECRYPTFS_REQ_ZOMBIE) {
 177                 rc = -EIO;
 178                 printk(KERN_WARNING "%s: Privileged open request dropped\n",
 179                        __func__);
 180                 goto out_unlock;
 181         }
 182         if (IS_ERR(*req->lower_file)) {
 183                 rc = PTR_ERR(*req->lower_file);
 184                 dget(lower_dentry);
 185                 mntget(lower_mnt);
 186                 (*lower_file) = dentry_open(lower_dentry, lower_mnt,
 187                                             (O_RDONLY | O_LARGEFILE));
 188                 if (IS_ERR(*lower_file)) {
 189                         rc = PTR_ERR(*req->lower_file);
 190                         (*lower_file) = NULL;
 191                         printk(KERN_WARNING "%s: Error attempting privileged "
 192                                "open of lower file with either RW or RO "
 193                                "perms; rc = [%d]. Giving up.\n",
 194                                __func__, rc);
 195                 }
 196         }
 197 out_unlock:
 198         mutex_unlock(&req->mux);
 199 out_free:
 200         kmem_cache_free(ecryptfs_open_req_cache, req);
 201 out:
 202         return rc;
 203 }