From 44bad9cbf7daa5ff7dd201e0c61e684b2e2eb971 Mon Sep 17 00:00:00 2001 From: Benjamin Kaduk Date: Fri, 24 Jan 2020 13:44:27 -0800 Subject: Code to thread-safety in ChangeCipherState The server-side ChangeCipherState processing stores the new cipher in the SSL_SESSION object, so that the new state can be used if this session gets resumed. However, writing to the session is only thread-safe for initial handshakes, as at other times the session object may be in a shared cache and in use by another thread at the same time. Reflect this invariant in the code by only writing to s->session->cipher when it is currently NULL (we do not cache sessions with no cipher). The code prior to this change would never actually change the (non-NULL) cipher value in a session object, since our server enforces that (pre-TLS-1.3) resumptions use the exact same cipher as the initial connection, and non-abbreviated renegotiations have produced a new session object before we get to this point. Regardless, include logic to detect such a condition and abort the handshake if it occurs, to avoid any risk of inadvertently using the wrong cipher on a connection. Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/10943) (cherry picked from commit 2e3ec2e1578977fca830a47fd7f521e290540e6d) --- ssl/statem/statem_srvr.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'ssl') diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c index e055cc2f3a..75619d9bca 100644 --- a/ssl/statem/statem_srvr.c +++ b/ssl/statem/statem_srvr.c @@ -743,7 +743,15 @@ WORK_STATE ossl_statem_server_pre_work(SSL *s, WORK_STATE wst) case TLS_ST_SW_CHANGE: if (SSL_IS_TLS13(s)) break; - s->session->cipher = s->s3->tmp.new_cipher; + /* Writes to s->session are only safe for initial handshakes */ + if (s->session->cipher == NULL) { + s->session->cipher = s->s3->tmp.new_cipher; + } else if (s->session->cipher != s->s3->tmp.new_cipher) { + SSLfatal(s, SSL_AD_INTERNAL_ERROR, + SSL_F_OSSL_STATEM_SERVER_PRE_WORK, + ERR_R_INTERNAL_ERROR); + return WORK_ERROR; + } if (!s->method->ssl3_enc->setup_key_block(s)) { /* SSLfatal() already called */ return WORK_ERROR; -- cgit v1.2.3