From: David Benjamin Date: Thu, 9 Feb 2017 20:13:13 +0000 (-0500) Subject: Don't read uninitialised data for short session IDs. X-Git-Tag: OpenSSL_1_1_0e~22 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=263390c32cd4f6baefd41346407eee51c1fd3fa2;p=openssl Don't read uninitialised data for short session IDs. While it's always safe to read |SSL_MAX_SSL_SESSION_ID_LENGTH| bytes from an |SSL_SESSION|'s |session_id| array, the hash function would do so with without considering if all those bytes had been written to. This change checks |session_id_length| before possibly reading uninitialised memory. Since the result of the hash function was already attacker controlled, and since a lookup of a short session ID will always fail, it doesn't appear that this is anything more than a clean up. In particular, |ssl_get_prev_session| uses a stack-allocated placeholder |SSL_SESSION| as a lookup key, so the |session_id| array may be uninitialised. This was originally found with libFuzzer and MSan in https://boringssl.googlesource.com/boringssl/+/e976e4349d693b4bbb97e1694f45be5a1b22c8c7, then by Robert Swiecki with honggfuzz and MSan here. Thanks to both. Reviewed-by: Geoff Thorpe Reviewed-by: Rich Salz (Merged from https://github.com/openssl/openssl/pull/2583) (cherry picked from commit bd5d27c1c6d3f83464ddf5124f18a2cac2cbb37f) --- diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c index 1698f13841..08af56b452 100644 --- a/ssl/ssl_lib.c +++ b/ssl/ssl_lib.c @@ -2305,13 +2305,21 @@ int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen, static unsigned long ssl_session_hash(const SSL_SESSION *a) { + const unsigned char *session_id = a->session_id; unsigned long l; + unsigned char tmp_storage[4]; + + if (a->session_id_length < sizeof(tmp_storage)) { + memset(tmp_storage, 0, sizeof(tmp_storage)); + memcpy(tmp_storage, a->session_id, a->session_id_length); + session_id = tmp_storage; + } l = (unsigned long) - ((unsigned int)a->session_id[0]) | - ((unsigned int)a->session_id[1] << 8L) | - ((unsigned long)a->session_id[2] << 16L) | - ((unsigned long)a->session_id[3] << 24L); + ((unsigned long)session_id[0]) | + ((unsigned long)session_id[1] << 8L) | + ((unsigned long)session_id[2] << 16L) | + ((unsigned long)session_id[3] << 24L); return (l); }