[nginx] SSL: disabled renegotiation detection in client mode.

[Sergey Kandaurov]

details:   http://hg.nginx.org/nginx/rev/ac9b1df5b246
branches:  
changeset: 6982:ac9b1df5b246
user:      Sergey Kandaurov <pluknet at nginx.com>
date:      Tue Apr 18 16:08:44 2017 +0300
description:
SSL: disabled renegotiation detection in client mode.

CVE-2009-3555 is no longer relevant and mitigated by the renegotiation
info extension (secure renegotiation).  On the other hand, unexpected
renegotiation still introduces potential security risks, and hence we do
not allow renegotiation on the server side, as we never request renegotiation.

On the client side the situation is different though.  There are backends
which explicitly request renegotiation, and disabled renegotiation
introduces interoperability problems.  This change allows renegotiation
on the client side, and fixes interoperability problems as observed with
such backends (ticket #872).

Additionally, with TLSv1.3 the SSL_CB_HANDSHAKE_START flag is currently set
by OpenSSL when receiving a NewSessionTicket message, and was detected by
nginx as a renegotiation attempt.  This looks like a bug in OpenSSL, though
this change also allows better interoperability till the problem is fixed.

diffstat:

 src/event/ngx_event_openssl.c |  4 +++-
 src/event/ngx_event_openssl.h |  5 +++++
 2 files changed, 8 insertions(+), 1 deletions(-)

diffs (29 lines):

diff -r 08dc60979133 -r ac9b1df5b246 src/event/ngx_event_openssl.c
--- a/src/event/ngx_event_openssl.c	Tue Apr 18 15:12:38 2017 +0300
+++ b/src/event/ngx_event_openssl.c	Tue Apr 18 16:08:44 2017 +0300
@@ -837,7 +837,9 @@ ngx_ssl_info_callback(const ngx_ssl_conn
     BIO               *rbio, *wbio;
     ngx_connection_t  *c;
 
-    if (where & SSL_CB_HANDSHAKE_START) {
+    if ((where & SSL_CB_HANDSHAKE_START)
+        && SSL_is_server((ngx_ssl_conn_t *) ssl_conn))
+    {
         c = ngx_ssl_get_connection((ngx_ssl_conn_t *) ssl_conn);
 
         if (c->ssl->handshaked) {
diff -r 08dc60979133 -r ac9b1df5b246 src/event/ngx_event_openssl.h
--- a/src/event/ngx_event_openssl.h	Tue Apr 18 15:12:38 2017 +0300
+++ b/src/event/ngx_event_openssl.h	Tue Apr 18 16:08:44 2017 +0300
@@ -54,6 +54,11 @@
 #define ngx_ssl_conn_t          SSL
 
 
+#if (OPENSSL_VERSION_NUMBER < 0x10002000L)
+#define SSL_is_server(s)        (s)->server
+#endif
+
+
 struct ngx_ssl_s {
     SSL_CTX                    *ctx;
     ngx_log_t                  *log;