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: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3425)

1 files changed, 20 insertions, 0 deletions

diff --git a/ssl/statem/extensions_cust.c b/ssl/statem/extensions_cust.c
index 2a21ec492c..e06fa9d1d7 100644
--- a/ssl/statem/extensions_cust.c
+++ b/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)
 {