Copy custom extension flags in a call to SSL_set_SSL_CTX()

The function SSL_set_SSL_CTX() can be used to swap the SSL_CTX used for
a connection as part of an SNI callback. One result of this is that the
s->cert structure is replaced. However this structure contains information
about any custom extensions that have been loaded. In particular flags are
set indicating whether a particular extension has been received in the
ClientHello. By replacing the s->cert structure we lose the custom
extension flag values, and it appears as if a client has not sent those
extensions.

SSL_set_SSL_CTX() should copy any flags for custom extensions that appear
in both the old and the new cert structure.

Fixes #2180
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3425)

ssl/ssl_lib.c

@@ -3596,6 +3596,12 @@ SSL_CTX *SSL_set_SSL_CTX(SSL *ssl, SSL_CTX *ctx)
     if (new_cert == NULL) {
         return NULL;
     }
+
+    if (!custom_exts_copy_flags(&new_cert->custext, &ssl->cert->custext)) {
+        ssl_cert_free(new_cert);
+        return NULL;
+    }
+
     ssl_cert_free(ssl->cert);
     ssl->cert = new_cert;
 

ssl/ssl_locl.h

@@ -2470,6 +2470,8 @@ __owur int custom_ext_add(SSL *s, int context, WPACKET *pkt, X509 *x,
 
 __owur int custom_exts_copy(custom_ext_methods *dst,
                             const custom_ext_methods *src);
+__owur int custom_exts_copy_flags(custom_ext_methods *dst,
+                                  const custom_ext_methods *src);
 void custom_exts_free(custom_ext_methods *exts);
 
 void ssl_comp_free_compression_methods_int(void);

ssl/statem/extensions_cust.c

@@ -231,6 +231,26 @@ int custom_ext_add(SSL *s, int context, WPACKET *pkt, X509 *x, size_t chainidx,
     return 1;
 }
 
+/* Copy the flags from src to dst for any extensions that exist in both */
+int custom_exts_copy_flags(custom_ext_methods *dst,
+                           const custom_ext_methods *src)
+{
+    size_t i;
+    custom_ext_method *methsrc = src->meths;
+
+    for (i = 0; i < src->meths_count; i++, methsrc++) {
+        custom_ext_method *methdst = custom_ext_find(dst, methsrc->role,
+                                                     methsrc->ext_type, NULL);
+
+        if (methdst == NULL)
+            continue;
+
+        methdst->ext_flags = methsrc->ext_flags;
+    }
+
+    return 1;
+}
+
 /* Copy table of custom extensions */
 int custom_exts_copy(custom_ext_methods *dst, const custom_ext_methods *src)
 {