From afdb05e9d61905220f09268535235288e6ba3a16 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Fri, 8 Sep 2017 16:15:58 -0700 Subject: [PATCH] lib/oid_registry.c: X.509: fix the buffer overflow in the utility function for OID string 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 Signed-off-by: "Lee, Chun-Yi" Reported-by: Pawel Wieczorkiewicz Cc: David Howells Cc: Rusty Russell Cc: Pawel Wieczorkiewicz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/oid_registry.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/oid_registry.c b/lib/oid_registry.c index 318f382a010d..41b9e50711a7 100644 --- a/lib/oid_registry.c +++ b/lib/oid_registry.c @@ -142,9 +142,9 @@ int sprint_oid(const void *data, size_t datasize, char *buffer, size_t bufsize) } ret += count = snprintf(buffer, bufsize, ".%lu", num); buffer += count; - bufsize -= count; - if (bufsize == 0) + if (bufsize <= count) return -ENOBUFS; + bufsize -= count; } return ret; -- 2.30.2