Call of memcmp with null pointers in obj_cmp()

The function obj_cmp() (file crypto/objects/obj_dat.c) can in some
situations call memcmp() with a null pointer and a zero length.

This is invalid behaviour. When compiling openssl with undefined
behaviour sanitizer (add -fsanitize=undefined to compile flags) this
can be seen. One example that triggers this behaviour is the pkcs7
command (but there are others, e.g. I've seen it with the timestamp
function):
apps/openssl pkcs7 -in test/testp7.pem

What happens is that obj_cmp takes objects of the type ASN1_OBJECT and
passes their ->data pointer to memcmp. Zero-sized ASN1_OBJECT
structures can have a null pointer as data.

RT#3816

Signed-off-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>

diff --git a/crypto/objects/obj_dat.c b/crypto/objects/obj_dat.c
index 3df7ff2457d4be132e64892385c29da64bb5c14c..6a068eef436a10e033c184db80cdef2dd97441fe 100644 (file)
--- a/crypto/objects/obj_dat.c
+++ b/crypto/objects/obj_dat.c
@@ -380,6 +380,8 @@ static int obj_cmp(const ASN1_OBJECT *const *ap, const unsigned int *bp)
     j = (a->length - b->length);
     if (j)
         return (j);
+    if (a->length == 0)
+        return 0;
     return (memcmp(a->data, b->data, a->length));
 }