Fix TLS 1.2 and no sigalgs.

For TLS 1.2 if we have no signature algorithms extension then lookup
using the complete table instead of (empty) shared signature algorithms
list so we pick up defaults.
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2301)

ssl/t1_lib.c

@@ -1278,6 +1278,7 @@ int tls12_get_sigandhash(SSL *s, WPACKET *pkt, const EVP_PKEY *pk,
 {
     int md_id, sig_id;
     size_t i;
+    const SIGALG_LOOKUP *curr;
 
     if (md == NULL)
         return 0;
@@ -1289,8 +1290,25 @@ int tls12_get_sigandhash(SSL *s, WPACKET *pkt, const EVP_PKEY *pk,
     if (SSL_IS_TLS13(s) && sig_id == EVP_PKEY_RSA)
         sig_id = EVP_PKEY_RSA_PSS;
 
+    if (s->s3->tmp.peer_sigalgs == NULL) {
+        /* Should never happen: we abort if no sigalgs extension and TLS 1.3 */
+        if (SSL_IS_TLS13(s))
+            return 0;
+        /* For TLS 1.2 and no sigalgs lookup using complete table */
+        for (i = 0, curr = sigalg_lookup_tbl; i < OSSL_NELEM(sigalg_lookup_tbl);
+             i++, curr++) {
+            if (curr->hash == md_id && curr->sig == sig_id) {
+                if (!WPACKET_put_bytes_u16(pkt, curr->sigalg))
+                    return 0;
+                *ispss = curr->sig == EVP_PKEY_RSA_PSS;
+                return 1;
+            }
+        }
+        return 0;
+    }
+
     for (i = 0; i < s->cert->shared_sigalgslen; i++) {
-        const SIGALG_LOOKUP *curr = s->cert->shared_sigalgs[i];
+        curr = s->cert->shared_sigalgs[i];
 
         /*
          * Look for matching key and hash. If key type is RSA also match PSS