stream-ssl: Set a session context ID string on our SSL_CTX.

In the finest OpenSSL tradition of putting important documentation only in
code comments, ssl/ssl_sess.c in the OpenSSL tree has the following comment
inside ssl_get_prev_session():

   /* We can't be sure if this session is being used out of
    * context, which is especially important for SSL_VERIFY_PEER.
    * The application should have used SSL[_CTX]_set_session_id_context.
    *
    * For this error case, we generate an error instead of treating
    * the event like a cache miss (otherwise it would be easy for
    * applications to effectively disable the session cache by
    * accident without anyone noticing).
    */

This meant that ovs-controller couldn't effectively cache SSL server
sessions and we got a weird error whenever ovs-vswitchd tried.

Bug #4448.
CC: David Tsai <dtsai@nicira.com>
CC: Jeremy Stribling <strib@nicira.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/stream-ssl.c b/lib/stream-ssl.c
index 6baf88ff1..ca3d218bf 100644
--- a/lib/stream-ssl.c
+++ b/lib/stream-ssl.c
@@ -1011,6 +1011,17 @@ do_ssl_init(void)
     SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT,
                        NULL);
 
+    /* We have to set a session context ID string in 'ctx' because OpenSSL
+     * otherwise refuses to use a cached session on the server side when
+     * SSL_VERIFY_PEER is set.  And it not only refuses to use the cached
+     * session, it actually generates an error and kills the connection.
+     * According to a comment in ssl_get_prev_session() in OpenSSL's
+     * ssl/ssl_sess.c, this is intentional behavior.
+     *
+     * Any context string is OK, as long as one is set. */
+    SSL_CTX_set_session_id_context(ctx, (const unsigned char *) PACKAGE,
+                                   strlen(PACKAGE));
+
     return 0;
 }