[PATCH 3.16 073/254] lib/oid_registry.c: X.509: fix the buffer overflow in the utility function for OID string

Ben Hutchings
2018-02-28T16:15:55Z

From: Takashi Iwai <tiwai@suse.de>

commit afdb05e9d61905220f09268535235288e6ba3a16 upstream.

The sprint_oid() utility function doesn't properly check the buffer size
that it causes that the warning in vsnprintf() be triggered. For
example on v4.1 kernel:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 2357 at lib/vsprintf.c:1867 vsnprintf+0x5a7/0x5c0()
...

We can trigger this issue by injecting maliciously crafted x509 cert in
DER format. Just using hex editor to change the length of OID to over
the length of the SEQUENCE container. For example:

0:d=0 hl=4 l= 980 cons: SEQUENCE
4:d=1 hl=4 l= 700 cons: SEQUENCE
8:d=2 hl=2 l= 3 cons: cont [ 0 ]
10:d=3 hl=2 l= 1 prim: INTEGER :02
13:d=2 hl=2 l= 9 prim: INTEGER :9B47FAF791E7D1E3
24:d=2 hl=2 l= 13 cons: SEQUENCE
26:d=3 hl=2 l= 9 prim: OBJECT :sha256WithRSAEncryption
37:d=3 hl=2 l= 0 prim: NULL
39:d=2 hl=2 l= 121 cons: SEQUENCE
41:d=3 hl=2 l= 22 cons: SET
43:d=4 hl=2 l= 20 cons: SEQUENCE <=== the SEQ length is 20
45:d=5 hl=2 l= 3 prim: OBJECT :organizationName
<=== the original length is 3, change the length of OID to over the length of SEQUENCE

Pawel Wieczorkiewicz reported this problem and Takashi Iwai provided
patch to fix it by checking the bufsize in sprint_oid().

Link: http://lkml.kernel.org/r/20170903021646.2080-1-jlee@suse.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
Reported-by: Pawel Wieczorkiewicz <pwieczorkiewicz@suse.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Pawel Wieczorkiewicz <pwieczorkiewicz@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
lib/oid_registry.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/lib/oid_registry.c
+++ b/lib/oid_registry.c
@@ -142,9 +142,9 @@ int sprint_oid(const void *data, size_t
}
ret += count = snprintf(buffer, bufsize, ".%lu", num);
buffer += count;
- bufsize -= count;
- if (bufsize == 0)
+ if (bufsize <= count)
return -ENOBUFS;
+ bufsize -= count;
}

return ret;