Ecryptfs: Add mount option to check uid of device being mounted = expect uid

Close a TOCTOU race for mounts done via ecryptfs-mount-private.  The mount
source (device) can be raced when the ownership test is done in userspace.
Provide Ecryptfs a means to force the uid check at mount time.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Cc: <stable@kernel.org>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>

1 files changed, 21 insertions, 2 deletions

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index 9f1bb747d77d..b4a6befb1216 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -175,6 +175,7 @@ enum { ecryptfs_opt_sig, ecryptfs_opt_ecryptfs_sig,
        ecryptfs_opt_encrypted_view, ecryptfs_opt_fnek_sig,
        ecryptfs_opt_fn_cipher, ecryptfs_opt_fn_cipher_key_bytes,
        ecryptfs_opt_unlink_sigs, ecryptfs_opt_mount_auth_tok_only,
+       ecryptfs_opt_check_dev_ruid,
        ecryptfs_opt_err };
 
 static const match_table_t tokens = {
@@ -191,6 +192,7 @@ static const match_table_t tokens = {
         {ecryptfs_opt_fn_cipher_key_bytes, "ecryptfs_fn_key_bytes=%u"},
         {ecryptfs_opt_unlink_sigs, "ecryptfs_unlink_sigs"},
         {ecryptfs_opt_mount_auth_tok_only, "ecryptfs_mount_auth_tok_only"},
+        {ecryptfs_opt_check_dev_ruid, "ecryptfs_check_dev_ruid"},
         {ecryptfs_opt_err, NULL}
 };
 
@@ -236,6 +238,7 @@ static void ecryptfs_init_mount_crypt_stat(
  * ecryptfs_parse_options
  * @sb: The ecryptfs super block
  * @options: The options passed to the kernel
+ * @check_ruid: set to 1 if device uid should be checked against the ruid
  *
  * Parse mount options:
  * debug=N         - ecryptfs_verbosity level for debug output
@@ -251,7 +254,8 @@ static void ecryptfs_init_mount_crypt_stat(
  *
  * Returns zero on success; non-zero on error
  */
-static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options)
+static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options,
+                                  uid_t *check_ruid)
 {
         char *p;
         int rc = 0;
@@ -276,6 +280,8 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options)
         char *cipher_key_bytes_src;
         char *fn_cipher_key_bytes_src;
 
+        *check_ruid = 0;
+
         if (!options) {
                 rc = -EINVAL;
                 goto out;
@@ -380,6 +386,9 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options)
                         mount_crypt_stat->flags |=
                                 ECRYPTFS_GLOBAL_MOUNT_AUTH_TOK_ONLY;
                         break;
+                case ecryptfs_opt_check_dev_ruid:
+                        *check_ruid = 1;
+                        break;
                 case ecryptfs_opt_err:
                 default:
                         printk(KERN_WARNING
@@ -475,6 +484,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
         const char *err = "Getting sb failed";
         struct inode *inode;
         struct path path;
+        uid_t check_ruid;
         int rc;
 
         sbi = kmem_cache_zalloc(ecryptfs_sb_info_cache, GFP_KERNEL);
@@ -483,7 +493,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
                 goto out;
         }
 
-        rc = ecryptfs_parse_options(sbi, raw_data);
+        rc = ecryptfs_parse_options(sbi, raw_data, &check_ruid);
         if (rc) {
                 err = "Error parsing options";
                 goto out;
@@ -521,6 +531,15 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
                         "known incompatibilities\n");
                 goto out_free;
         }
+
+        if (check_ruid && path.dentry->d_inode->i_uid != current_uid()) {
+                rc = -EPERM;
+                printk(KERN_ERR "Mount of device (uid: %d) not owned by "
+                       "requested user (uid: %d)\n",
+                       path.dentry->d_inode->i_uid, current_uid());
+                goto out_free;
+        }
+
         ecryptfs_set_superblock_lower(s, path.dentry->d_sb);
         s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
         s->s_blocksize = path.dentry->d_sb->s_blocksize;