From bd5d27c1c6d3f83464ddf5124f18a2cac2cbb37f Mon Sep 17 00:00:00 2001 From: David Benjamin Date: Thu, 9 Feb 2017 15:13:13 -0500 Subject: [PATCH] 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) --- ssl/ssl_lib.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c index e4eec4a949..3b18c3ebfd 100644 --- a/ssl/ssl_lib.c +++ b/ssl/ssl_lib.c @@ -2391,13 +2391,21 @@ 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); } -- 2.25.1