Disallow SSL session tickets.

We don't actually support session tickets, since we do not create an SSL
session identifier.  But it seems that OpenSSL will issue a session ticket
on-demand anyway, which will then fail when used.  This results in
reconnection failures when using ticket-aware client-side SSL libraries
(such as the Npgsql .NET driver), as reported by Shay Rojansky.

To fix, just tell OpenSSL not to issue tickets.  At some point in the
far future, we might consider enabling tickets instead.  But the security
implications of that aren't entirely clear; and besides it would have
little benefit except for very short-lived database connections, which is
Something We're Bad At anyhow.  It would take a lot of other work to get
to a point where that would really be an exciting thing to do.

While at it, also tell OpenSSL not to use a session cache.  This doesn't
really do anything, since a backend would never populate the cache anyway,
but it might gain some micro-efficiencies and/or reduce security
exposures.

Patch by me, per discussion with Heikki Linnakangas and Shay Rojansky.
Back-patch to all supported versions.

Discussion: https://postgr.es/m/CADT4RqBU8N-csyZuzaook-c795dt22Zcwg1aHWB6tfVdAkodZA@mail.gmail.com

diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index c6573b40e7ba6e70d293e9551ac9a9323d2ae368..b620ee73a10905ea63a0402839efa6c4ef9ddae7 100644 (file)
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -935,6 +935,14 @@ initialize_SSL(void)
    SSL_CTX_set_tmp_dh_callback(SSL_context, tmp_dh_cb);
    SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_DH_USE | SSL_OP_NO_SSLv2);
 
+   /* disallow SSL session tickets */
+#ifdef SSL_OP_NO_TICKET            /* added in openssl 0.9.8f */
+   SSL_CTX_set_options(SSL_context, SSL_OP_NO_TICKET);
+#endif
+
+   /* disallow SSL session caching, too */
+   SSL_CTX_set_session_cache_mode(SSL_context, SSL_SESS_CACHE_OFF);
+
    /* set up the allowed cipher list */
    if (SSL_CTX_set_cipher_list(SSL_context, SSLCipherSuites) != 1)
        elog(FATAL, "could not set the cipher list (no valid ciphers available)");