From b52867a9f618bb955bed2a3ce3db4d4f97ed8e5d Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Tue, 5 Mar 2024 15:43:53 +0000 Subject: [PATCH] Fix unconstrained session cache growth in TLSv1.3 In TLSv1.3 we create a new session object for each ticket that we send. We do this by duplicating the original session. If SSL_OP_NO_TICKET is in use then the new session will be added to the session cache. However, if early data is not in use (and therefore anti-replay protection is being used), then multiple threads could be resuming from the same session simultaneously. If this happens and a problem occurs on one of the threads, then the original session object could be marked as not_resumable. When we duplicate the session object this not_resumable status gets copied into the new session object. The new session object is then added to the session cache even though it is not_resumable. Subsequently, another bug means that the session_id_length is set to 0 for sessions that are marked as not_resumable - even though that session is still in the cache. Once this happens the session can never be removed from the cache. When that object gets to be the session cache tail object the cache never shrinks again and grows indefinitely. CVE-2024-2511 Reviewed-by: Neil Horman Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/24044) (cherry picked from commit 7e4d731b1c07201ad9374c1cd9ac5263bdf35bce) --- ssl/ssl_lib.c | 5 +++-- ssl/ssl_sess.c | 28 ++++++++++++++++++++++------ ssl/statem/statem_srvr.c | 5 ++--- 3 files changed, 27 insertions(+), 11 deletions(-) Index: openssl-1.1.1w/ssl/ssl_lib.c =================================================================== --- openssl-1.1.1w.orig/ssl/ssl_lib.c +++ openssl-1.1.1w/ssl/ssl_lib.c @@ -3524,9 +3524,10 @@ void ssl_update_cache(SSL *s, int mode) /* * If the session_id_length is 0, we are not supposed to cache it, and it - * would be rather hard to do anyway :-) + * would be rather hard to do anyway :-). Also if the session has already + * been marked as not_resumable we should not cache it for later reuse. */ - if (s->session->session_id_length == 0) + if (s->session->session_id_length == 0 || s->session->not_resumable) return; /* Index: openssl-1.1.1w/ssl/ssl_sess.c =================================================================== --- openssl-1.1.1w.orig/ssl/ssl_sess.c +++ openssl-1.1.1w/ssl/ssl_sess.c @@ -94,16 +94,11 @@ SSL_SESSION *SSL_SESSION_new(void) return ss; } -SSL_SESSION *SSL_SESSION_dup(SSL_SESSION *src) -{ - return ssl_session_dup(src, 1); -} - /* * Create a new SSL_SESSION and duplicate the contents of |src| into it. If * ticket == 0 then no ticket information is duplicated, otherwise it is. */ -SSL_SESSION *ssl_session_dup(SSL_SESSION *src, int ticket) +static SSL_SESSION *ssl_session_dup_intern(SSL_SESSION *src, int ticket) { SSL_SESSION *dest; @@ -226,6 +221,27 @@ SSL_SESSION *ssl_session_dup(SSL_SESSION return NULL; } +SSL_SESSION *SSL_SESSION_dup(SSL_SESSION *src) +{ + return ssl_session_dup_intern(src, 1); +} + +/* + * Used internally when duplicating a session which might be already shared. + * We will have resumed the original session. Subsequently we might have marked + * it as non-resumable (e.g. in another thread) - but this copy should be ok to + * resume from. + */ +SSL_SESSION *ssl_session_dup(SSL_SESSION *src, int ticket) +{ + SSL_SESSION *sess = ssl_session_dup_intern(src, ticket); + + if (sess != NULL) + sess->not_resumable = 0; + + return sess; +} + const unsigned char *SSL_SESSION_get_id(const SSL_SESSION *s, unsigned int *len) { if (len) Index: openssl-1.1.1w/ssl/statem/statem_srvr.c =================================================================== --- openssl-1.1.1w.orig/ssl/statem/statem_srvr.c +++ openssl-1.1.1w/ssl/statem/statem_srvr.c @@ -2403,9 +2403,8 @@ int tls_construct_server_hello(SSL *s, W * so the following won't overwrite an ID that we're supposed * to send back. */ - if (s->session->not_resumable || - (!(s->ctx->session_cache_mode & SSL_SESS_CACHE_SERVER) - && !s->hit)) + if (!(s->ctx->session_cache_mode & SSL_SESS_CACHE_SERVER) + && !s->hit) s->session->session_id_length = 0; if (usetls13) {