Factor out ALPN extension format check

The ALPN extension must contain a non-empty list of protocol names.
Split a check of this out of tlsext_alpn_server_parse() so that it
can be reused elsewhere in the library.

ok jsing

diff --git a/lib/libssl/ssl_tlsext.c b/lib/libssl/ssl_tlsext.c
index 6063991..781d40d 100644 (file)
--- a/lib/libssl/ssl_tlsext.c
+++ b/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.121 2022/07/17 14:54:10 jsing Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.122 2022/07/20 13:35:05 tb Exp $ */
 /*
  * Copyright (c) 2016, 2017, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -62,30 +62,42 @@ tlsext_alpn_client_build(SSL *s, uint16_t msg_type, CBB *cbb)
        return 1;
 }
 
+int
+tlsext_alpn_check_format(CBS *cbs)
+{
+       CBS proto_name_list;
+
+       if (CBS_len(cbs) == 0)
+               return 0;
+
+       CBS_dup(cbs, &proto_name_list);
+       while (CBS_len(&proto_name_list) > 0) {
+               CBS proto_name;
+
+               if (!CBS_get_u8_length_prefixed(&proto_name_list, &proto_name))
+                       return 0;
+               if (CBS_len(&proto_name) == 0)
+                       return 0;
+       }
+
+       return 1;
+}
+
 int
 tlsext_alpn_server_parse(SSL *s, uint16_t msg_types, CBS *cbs, int *alert)
 {
-       CBS proto_name_list, alpn;
+       CBS alpn;
        const unsigned char *selected;
        unsigned char selected_len;
        int r;
 
        if (!CBS_get_u16_length_prefixed(cbs, &alpn))
                goto err;
-       if (CBS_len(&alpn) < 2)
-               goto err;
        if (CBS_len(cbs) != 0)
                goto err;
 
-       CBS_dup(&alpn, &proto_name_list);
-       while (CBS_len(&proto_name_list) > 0) {
-               CBS proto_name;
-
-               if (!CBS_get_u8_length_prefixed(&proto_name_list, &proto_name))
-                       goto err;
-               if (CBS_len(&proto_name) == 0)
-                       goto err;
-       }
+       if (!tlsext_alpn_check_format(&alpn))
+               goto err;
 
        if (s->ctx->internal->alpn_select_cb == NULL)
                return 1;

diff --git a/lib/libssl/ssl_tlsext.h b/lib/libssl/ssl_tlsext.h
index 268b274..393ee5d 100644 (file)
--- a/lib/libssl/ssl_tlsext.h
+++ b/lib/libssl/ssl_tlsext.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.h,v 1.30 2022/06/29 17:39:20 beck Exp $ */
+/* $OpenBSD: ssl_tlsext.h,v 1.31 2022/07/20 13:35:05 tb Exp $ */
 /*
  * Copyright (c) 2016, 2017 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -31,6 +31,7 @@
 
 __BEGIN_HIDDEN_DECLS
 
+int tlsext_alpn_check_format(CBS *cbs);
 int tlsext_alpn_client_needs(SSL *s, uint16_t msg_type);
 int tlsext_alpn_client_build(SSL *s, uint16_t msg_type, CBB *cbb);
 int tlsext_alpn_client_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert);