Actually parse the ALPN extension in a client hello, even if no ALPN

callback has been installed. This ensures that the ALPN extension is valid
and avoids leaving unprocessed extension data, which leads to a decode
error.

Found the hard way by jsg@

1 files changed, 4 insertions, 4 deletions

diff --git a/src/lib/libssl/ssl_tlsext.c b/src/lib/libssl/ssl_tlsext.c
index 2438b90d04..6b60ccd27f 100644
--- a/src/lib/libssl/ssl_tlsext.c
+++ b/src/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.12 2017/08/27 02:58:04 doug Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.13 2017/08/29 17:24:12 jsing Exp $ */
 /*
  * Copyright (c) 2016, 2017 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -61,9 +61,6 @@ tlsext_alpn_clienthello_parse(SSL *s, CBS *cbs, int *alert)
         unsigned char selected_len;
         int r;
 
-        if (s->ctx->internal->alpn_select_cb == NULL)
-                return 1;
-
         if (!CBS_get_u16_length_prefixed(cbs, &alpn))
                 goto err;
         if (CBS_len(&alpn) < 2)
@@ -81,6 +78,9 @@ tlsext_alpn_clienthello_parse(SSL *s, CBS *cbs, int *alert)
                         goto err;
         }
 
+        if (s->ctx->internal->alpn_select_cb == NULL)
+                return 1;
+
         r = s->ctx->internal->alpn_select_cb(s, &selected, &selected_len,
             CBS_data(&alpn), CBS_len(&alpn),
             s->ctx->internal->alpn_select_cb_arg);