From 5a90787578603c7207dfc1be2dad5f09780bbae8 Mon Sep 17 00:00:00 2001
From: John Johansen <john.johansen@canonical.com>
Date: Thu, 11 Aug 2011 00:48:00 -0700
Subject: [PATCH] Add mount option to check uid of device being mounted = expect uid, CVE-2011-1833

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.

(backported from commit 764355487ea220fdc2faf128d577d7f679b91f97)
CVE-2011-1833
BugLink: http://bugs.launchpad.net/bugs/732628

Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 fs/ecryptfs/main.c |   29 ++++++++++++++++++++++++-----
 1 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index cbd4e18..d5581f6 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -208,7 +208,8 @@ enum { ecryptfs_opt_sig, ecryptfs_opt_ecryptfs_sig,
        ecryptfs_opt_passthrough, ecryptfs_opt_xattr_metadata,
        ecryptfs_opt_encrypted_view, ecryptfs_opt_fnek_sig,
        ecryptfs_opt_fn_cipher, ecryptfs_opt_fn_cipher_key_bytes,
-       ecryptfs_opt_unlink_sigs, ecryptfs_opt_err };
+       ecryptfs_opt_unlink_sigs, ecryptfs_opt_check_dev_ruid,
+       ecryptfs_opt_err };
 
 static const match_table_t tokens = {
 	{ecryptfs_opt_sig, "sig=%s"},
@@ -223,6 +224,7 @@ static const match_table_t tokens = {
 	{ecryptfs_opt_fn_cipher, "ecryptfs_fn_cipher=%s"},
 	{ecryptfs_opt_fn_cipher_key_bytes, "ecryptfs_fn_key_bytes=%u"},
 	{ecryptfs_opt_unlink_sigs, "ecryptfs_unlink_sigs"},
+	{ecryptfs_opt_check_dev_ruid, "ecryptfs_check_dev_ruid"},
 	{ecryptfs_opt_err, NULL}
 };
 
@@ -266,6 +268,7 @@ static void ecryptfs_init_mount_crypt_stat(
  * ecryptfs_parse_options
  * @sb: The ecryptfs super block
  * @options: The options pased 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
@@ -281,7 +284,8 @@ 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;
@@ -306,6 +310,8 @@ 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;
@@ -406,6 +412,9 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options)
 		case ecryptfs_opt_unlink_sigs:
 			mount_crypt_stat->flags |= ECRYPTFS_UNLINK_SIGS;
 			break;
+		case ecryptfs_opt_check_dev_ruid:
+			*check_ruid = 1;
+			break;
 		case ecryptfs_opt_err:
 		default:
 			printk(KERN_WARNING
@@ -494,7 +503,7 @@ static struct file_system_type ecryptfs_fs_type;
  * ecryptfs_interpose to create our initial inode and super block
  * struct.
  */
-static int ecryptfs_read_super(struct super_block *sb, const char *dev_name)
+static int ecryptfs_read_super(struct super_block *sb, const char *dev_name, uid_t check_ruid)
 {
 	struct path path;
 	int rc;
@@ -511,6 +520,15 @@ static int ecryptfs_read_super(struct super_block *sb, const char *dev_name)
 			"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(sb, path.dentry->d_sb);
 	sb->s_maxbytes = path.dentry->d_sb->s_maxbytes;
 	sb->s_blocksize = path.dentry->d_sb->s_blocksize;
@@ -549,6 +567,7 @@ static int ecryptfs_get_sb(struct file_system_type *fs_type, int flags,
 	struct ecryptfs_dentry_info *root_info;
 	const char *err = "Getting sb failed";
 	int rc;
+	uid_t check_ruid;
 
 	sbi = kmem_cache_zalloc(ecryptfs_sb_info_cache, GFP_KERNEL);
 	if (!sbi) {
@@ -556,7 +575,7 @@ static int ecryptfs_get_sb(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;
@@ -601,7 +620,7 @@ static int ecryptfs_get_sb(struct file_system_type *fs_type, int flags,
 	/* ->kill_sb() will take care of root_info */
 	ecryptfs_set_dentry_private(s->s_root, root_info);
 	s->s_flags |= MS_ACTIVE;
-	rc = ecryptfs_read_super(s, dev_name);
+	rc = ecryptfs_read_super(s, dev_name, check_ruid);
 	if (rc) {
 		deactivate_locked_super(s);
 		err = "Reading sb failed";
-- 
1.7.0.4

