Implement handlers for the psk_key_exchange_modes extensions.

ok jsing

2 files changed, 96 insertions, 3 deletions

diff --git a/src/lib/libssl/ssl_tlsext.c b/src/lib/libssl/ssl_tlsext.c
index f93f44ceba..de2c1c19d2 100644
--- a/src/lib/libssl/ssl_tlsext.c
+++ b/src/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.110 2022/02/05 14:54:10 jsing Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.111 2022/06/03 13:29:39 tb Exp $ */
 /*
  * Copyright (c) 2016, 2017, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -1832,6 +1832,76 @@ tlsext_cookie_client_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert)
         return 0;
 }
 
+/*
+ * Pre-Shared Key Exchange Modes - RFC 8446, 4.2.9.
+ */
+
+int
+tlsext_psk_kex_modes_client_needs(SSL *s, uint16_t msg_type)
+{
+        return (s->s3->hs.tls13.use_psk_dhe_ke &&
+            s->s3->hs.our_max_tls_version >= TLS1_3_VERSION);
+}
+
+int
+tlsext_psk_kex_modes_client_build(SSL *s, uint16_t msg_type, CBB *cbb)
+{
+        CBB ke_modes;
+
+        if (!CBB_add_u8_length_prefixed(cbb, &ke_modes))
+                return 0;
+
+        /* Only indicate support for PSK with DHE key establishment. */
+        if (!CBB_add_u8(&ke_modes, TLS13_PSK_DHE_KE))
+                return 0;
+
+        if (!CBB_flush(cbb))
+                return 0;
+
+        return 1;
+}
+
+int
+tlsext_psk_kex_modes_server_parse(SSL *s, uint16_t msg_type, CBS *cbs,
+    int *alert)
+{
+        CBS ke_modes;
+        uint8_t ke_mode;
+
+        if (!CBS_get_u8_length_prefixed(cbs, &ke_modes))
+                return 0;
+
+        while (CBS_len(&ke_modes) > 0) {
+                if (!CBS_get_u8(&ke_modes, &ke_mode))
+                        return 0;
+
+                if (ke_mode == TLS13_PSK_DHE_KE)
+                        s->s3->hs.tls13.use_psk_dhe_ke = 1;
+        }
+
+        return 1;
+}
+
+int
+tlsext_psk_kex_modes_server_needs(SSL *s, uint16_t msg_type)
+{
+        /* Servers MUST NOT send this extension. */
+        return 0;
+}
+
+int
+tlsext_psk_kex_modes_server_build(SSL *s, uint16_t msg_type, CBB *cbb)
+{
+        return 0;
+}
+
+int
+tlsext_psk_kex_modes_client_parse(SSL *s, uint16_t msg_type, CBS *cbs,
+    int *alert)
+{
+        return 0;
+}
+
 struct tls_extension_funcs {
         int (*needs)(SSL *s, uint16_t msg_type);
         int (*build)(SSL *s, uint16_t msg_type, CBB *cbb);
@@ -2018,8 +2088,22 @@ static const struct tls_extension tls_extensions[] = {
                         .build = tlsext_srtp_server_build,
                         .parse = tlsext_srtp_server_parse,
                 },
-        }
+        },
 #endif /* OPENSSL_NO_SRTP */
+        {
+                .type = TLSEXT_TYPE_psk_key_exchange_modes,
+                .messages = SSL_TLSEXT_MSG_CH,
+                .client = {
+                        .needs = tlsext_psk_kex_modes_client_needs,
+                        .build = tlsext_psk_kex_modes_client_build,
+                        .parse = tlsext_psk_kex_modes_client_parse,
+                },
+                .server = {
+                        .needs = tlsext_psk_kex_modes_server_needs,
+                        .build = tlsext_psk_kex_modes_server_build,
+                        .parse = tlsext_psk_kex_modes_server_parse,
+                },
+        },
 };
 
 #define N_TLS_EXTENSIONS (sizeof(tls_extensions) / sizeof(*tls_extensions))
diff --git a/src/lib/libssl/ssl_tlsext.h b/src/lib/libssl/ssl_tlsext.h
index b4c135fdf1..5f5a852abe 100644
--- a/src/lib/libssl/ssl_tlsext.h
+++ b/src/lib/libssl/ssl_tlsext.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.h,v 1.27 2021/11/01 16:37:17 jsing Exp $ */
+/* $OpenBSD: ssl_tlsext.h,v 1.28 2022/06/03 13:29:39 tb Exp $ */
 /*
  * Copyright (c) 2016, 2017 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -119,6 +119,15 @@ int tlsext_cookie_server_needs(SSL *s, uint16_t msg_type);
 int tlsext_cookie_server_build(SSL *s, uint16_t msg_type, CBB *cbb);
 int tlsext_cookie_server_parse(SSL *s, uint16_t msg_type, CBS *cbs, int *alert);
 
+int tlsext_psk_kex_modes_client_needs(SSL *s, uint16_t msg_type);
+int tlsext_psk_kex_modes_client_build(SSL *s, uint16_t msg_type, CBB *cbb);
+int tlsext_psk_kex_modes_client_parse(SSL *s, uint16_t msg_type, CBS *cbs,
+    int *alert);
+int tlsext_psk_kex_modes_server_needs(SSL *s, uint16_t msg_type);
+int tlsext_psk_kex_modes_server_build(SSL *s, uint16_t msg_type, CBB *cbb);
+int tlsext_psk_kex_modes_server_parse(SSL *s, uint16_t msg_type, CBS *cbs,
+    int *alert);
+
 #ifndef OPENSSL_NO_SRTP
 int tlsext_srtp_client_needs(SSL *s, uint16_t msg_type);
 int tlsext_srtp_client_build(SSL *s, uint16_t msg_type, CBB *cbb);