From e3743355e840dadff0b09582942b7a90db607894 Mon Sep 17 00:00:00 2001 From: Benjamin Kaduk Date: Wed, 9 Aug 2017 08:14:24 -0500 Subject: Don't modify resumed session objects If s->hit is set, s->session corresponds to a session created on a previous connection, and is a data structure that is potentially shared across other SSL objects. As such, there are thread-safety issues with modifying the structure without taking its lock (and of course all corresponding read accesses would also need to take the lock as well), which have been observed to cause double-frees. Regardless of thread-safety, the resumed session object is intended to reflect parameters of the connection that created the session, and modifying it to reflect the parameters from the current connection is confusing. So, modifications to the session object during ClientHello processing should only be performed on new connections, i.e., those where s->hit is not set. The code mostly got this right, providing such checks when processing SNI and EC point formats, but the supported groups (formerly supported curves) extension was missing it, which is fixed by this commit. However, TLS 1.3 makes the suppported_groups extension mandatory (when using (EC)DHE, which is the normal case), checking for the group list in the key_share extension processing. But, TLS 1.3 only [0] supports session tickets for session resumption, so the session object in question is the output of d2i_SSL_SESSION(), and will not be shared across SSL objects. Thus, it is safe to modify s->session for TLS 1.3 connections. [0] A psk_find_session callback can also be used, but the restriction that each callback execution must produce a distinct SSL_SESSION structure can be documented when the psk_find_session callback documentation is completed. Reviewed-by: Andy Polyakov (Merged from https://github.com/openssl/openssl/pull/4123) --- ssl/statem/extensions_srvr.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/ssl/statem/extensions_srvr.c b/ssl/statem/extensions_srvr.c index 9fe58a780a..a3c2fbf7de 100644 --- a/ssl/statem/extensions_srvr.c +++ b/ssl/statem/extensions_srvr.c @@ -641,14 +641,16 @@ int tls_parse_ctos_supported_groups(SSL *s, PACKET *pkt, unsigned int context, return 0; } - OPENSSL_free(s->session->ext.supportedgroups); - s->session->ext.supportedgroups = NULL; - s->session->ext.supportedgroups_len = 0; - if (!PACKET_memdup(&supported_groups_list, - &s->session->ext.supportedgroups, - &s->session->ext.supportedgroups_len)) { - *al = SSL_AD_INTERNAL_ERROR; - return 0; + if (!s->hit || SSL_IS_TLS13(s)) { + OPENSSL_free(s->session->ext.supportedgroups); + s->session->ext.supportedgroups = NULL; + s->session->ext.supportedgroups_len = 0; + if (!PACKET_memdup(&supported_groups_list, + &s->session->ext.supportedgroups, + &s->session->ext.supportedgroups_len)) { + *al = SSL_AD_INTERNAL_ERROR; + return 0; + } } return 1; -- cgit v1.2.3