[PATCH 3.16 322/328] KEYS: encrypted: fix buffer overread in valid_master_desc()

Ben Hutchings
2018-12-09T22:19:09Z

From: Eric Biggers <ebiggers@google.com>

commit 794b4bc292f5d31739d89c0202c54e7dc9bc3add upstream.

With the 'encrypted' key type it was possible for userspace to provide a
data blob ending with a master key description shorter than expected,
e.g. 'keyctl add encrypted desc "new x" @s'. When validating such a
master key description, validate_master_desc() could read beyond the end
of the buffer. Fix this by using strncmp() instead of memcmp(). [Also
clean up the code to deduplicate some logic.]

Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
security/keys/encrypted-keys/encrypted.c | 31 ++++++++++++------------
1 file changed, 15 insertions(+), 16 deletions(-)

--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -141,23 +141,22 @@ static int valid_ecryptfs_desc(const cha
*/
static int valid_master_desc(const char *new_desc, const char *orig_desc)
{
- if (!memcmp(new_desc, KEY_TRUSTED_PREFIX, KEY_TRUSTED_PREFIX_LEN)) {
- if (strlen(new_desc) == KEY_TRUSTED_PREFIX_LEN)
- goto out;
- if (orig_desc)
- if (memcmp(new_desc, orig_desc, KEY_TRUSTED_PREFIX_LEN))
- goto out;
- } else if (!memcmp(new_desc, KEY_USER_PREFIX, KEY_USER_PREFIX_LEN)) {
- if (strlen(new_desc) == KEY_USER_PREFIX_LEN)
- goto out;
- if (orig_desc)
- if (memcmp(new_desc, orig_desc, KEY_USER_PREFIX_LEN))
- goto out;
- } else
- goto out;
+ int prefix_len;
+
+ if (!strncmp(new_desc, KEY_TRUSTED_PREFIX, KEY_TRUSTED_PREFIX_LEN))
+ prefix_len = KEY_TRUSTED_PREFIX_LEN;
+ else if (!strncmp(new_desc, KEY_USER_PREFIX, KEY_USER_PREFIX_LEN))
+ prefix_len = KEY_USER_PREFIX_LEN;
+ else
+ return -EINVAL;
+
+ if (!new_desc[prefix_len])
+ return -EINVAL;
+
+ if (orig_desc && strncmp(new_desc, orig_desc, prefix_len))
+ return -EINVAL;
+
return 0;
-out:
- return -EINVAL;
}

/*