From: Matt Caswell <matt@openssl.org>
Date: Fri, 21 Jun 2024 10:51:54 +0000 (+0100)
Subject: Add ALPN validation in the client
X-Git-Tag: openssl-3.4.0-alpha1~436
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=238fa464d6e38aa2c92af70ef9580c74cff512e4;p=thirdparty%2Fopenssl.git

Add ALPN validation in the client

The ALPN protocol selected by the server must be one that we originally
advertised. We should verify that it is.

Follow on from CVE-2024-5535

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24716)
---

diff --git a/ssl/statem/extensions_clnt.c b/ssl/statem/extensions_clnt.c
index f24db5f570d..1c955f414eb 100644
--- a/ssl/statem/extensions_clnt.c
+++ b/ssl/statem/extensions_clnt.c
@@ -1628,6 +1628,8 @@ int tls_parse_stoc_alpn(SSL_CONNECTION *s, PACKET *pkt, unsigned int context,
                         X509 *x, size_t chainidx)
 {
     size_t len;
+    PACKET confpkt, protpkt;
+    int valid = 0;
 
     /* We must have requested it. */
     if (!s->s3.alpn_sent) {
@@ -1646,6 +1648,28 @@ int tls_parse_stoc_alpn(SSL_CONNECTION *s, PACKET *pkt, unsigned int context,
         SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_R_BAD_EXTENSION);
         return 0;
     }
+
+    /* It must be a protocol that we sent */
+    if (!PACKET_buf_init(&confpkt, s->ext.alpn, s->ext.alpn_len)) {
+        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
+        return 0;
+    }
+    while (PACKET_get_length_prefixed_1(&confpkt, &protpkt)) {
+        if (PACKET_remaining(&protpkt) != len)
+            continue;
+        if (memcmp(PACKET_data(pkt), PACKET_data(&protpkt), len) == 0) {
+            /* Valid protocol found */
+            valid = 1;
+            break;
+        }
+    }
+
+    if (!valid) {
+        /* The protocol sent from the server does not match one we advertised */
+        SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_R_BAD_EXTENSION);
+        return 0;
+    }
+
     OPENSSL_free(s->s3.alpn_selected);
     s->s3.alpn_selected = OPENSSL_malloc(len);
     if (s->s3.alpn_selected == NULL) {