Tolerate a Certificate using a non-supported group on server side

If a server has been configured to use an ECDSA certificate, we should
allow it regardless of whether the server's own supported groups list
includes the certificate's group.

Fixes #2033

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5601)

ssl/ssl_locl.h

diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index eae5788..1c3ee35 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -2453,7 +2453,7 @@
 #  ifndef OPENSSL_NO_EC
 
 __owur const TLS_GROUP_INFO *tls1_group_id_lookup(uint16_t curve_id);
-__owur int tls1_check_group_id(SSL *s, uint16_t group_id);
+__owur int tls1_check_group_id(SSL *s, uint16_t group_id, int check_own_curves);
 __owur uint16_t tls1_shared_group(SSL *s, int nmatch);
 __owur int tls1_set_groups(uint16_t **pext, size_t *pextlen,
                            int *curves, size_t ncurves);

ssl/statem/statem_clnt.c

diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index e940fc8..29db4bc 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -2192,7 +2192,8 @@
      * Check curve is named curve type and one of our preferences, if not
      * server has sent an invalid curve.
      */
-    if (curve_type != NAMED_CURVE_TYPE || !tls1_check_group_id(s, curve_id)) {
+    if (curve_type != NAMED_CURVE_TYPE
+            || !tls1_check_group_id(s, curve_id, 1)) {
         SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER, SSL_F_TLS_PROCESS_SKE_ECDHE,
                  SSL_R_WRONG_CURVE);
         return 0;

ssl/t1_lib.c

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 174d7de..cf5f783 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -467,7 +467,7 @@
 }
 
 /* Check a group id matches preferences */
-int tls1_check_group_id(SSL *s, uint16_t group_id)
+int tls1_check_group_id(SSL *s, uint16_t group_id, int check_own_groups)
     {
     const uint16_t *groups;
     size_t groups_len;
@@ -491,10 +491,12 @@
         }
     }
 
-    /* Check group is one of our preferences */
-    tls1_get_supported_groups(s, &groups, &groups_len);
-    if (!tls1_in_list(group_id, groups, groups_len))
-        return 0;
+    if (check_own_groups) {
+        /* Check group is one of our preferences */
+        tls1_get_supported_groups(s, &groups, &groups_len);
+        if (!tls1_in_list(group_id, groups, groups_len))
+            return 0;
+    }
 
     if (!tls_curve_allowed(s, group_id, SSL_SECOP_CURVE_CHECK))
         return 0;
@@ -554,7 +556,11 @@
     if (!tls1_check_pkey_comp(s, pkey))
         return 0;
     group_id = tls1_get_group_id(pkey);
-    if (!tls1_check_group_id(s, group_id))
+    /*
+     * For a server we allow the certificate to not be in our list of supported
+     * groups.
+     */
+    if (!tls1_check_group_id(s, group_id, !s->server))
         return 0;
     /*
      * Special case for suite B. We *MUST* sign using SHA256+P-256 or
@@ -601,9 +607,9 @@
      * curves permitted.
      */
     if (cid == TLS1_CK_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256)
-        return tls1_check_group_id(s, TLSEXT_curve_P_256);
+        return tls1_check_group_id(s, TLSEXT_curve_P_256, 1);
     if (cid == TLS1_CK_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384)
-        return tls1_check_group_id(s, TLSEXT_curve_P_384);
+        return tls1_check_group_id(s, TLSEXT_curve_P_384, 1);
 
     return 0;
 }
@@ -979,7 +985,7 @@
         }
         if (!SSL_IS_TLS13(s)) {
             /* Check curve matches extensions */
-            if (!tls1_check_group_id(s, tls1_get_group_id(pkey))) {
+            if (!tls1_check_group_id(s, tls1_get_group_id(pkey), 1)) {
                 SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER,
                          SSL_F_TLS12_CHECK_PEER_SIGALG, SSL_R_WRONG_CURVE);
                 return 0;