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

…ect 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>
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1 parent 99b373f commit 764355487ea220fdc2faf128d577d7f679b91f97 John Johansen committed with Tyler Hicks Jul 22, 2011
Showing with 21 additions and 2 deletions.
  1. +21 −2 fs/ecryptfs/main.c
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@@ -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;

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