Fix some instances of the wrong alert type being sent

In a few places we sent an internal_error alert instead of a decode_error.

Fixes #5213
Fixes #5214

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5219)

ssl/statem/extensions_clnt.c

diff --git a/ssl/statem/extensions_clnt.c b/ssl/statem/extensions_clnt.c
index dbb8812..5441e98 100644
--- a/ssl/statem/extensions_clnt.c
+++ b/ssl/statem/extensions_clnt.c
@@ -1273,7 +1273,7 @@
 int tls_parse_stoc_ec_pt_formats(SSL *s, PACKET *pkt, unsigned int context,
                                  X509 *x, size_t chainidx)
 {
-    unsigned int ecpointformats_len;
+    size_t ecpointformats_len;
     PACKET ecptformatlist;
 
     if (!PACKET_as_length_prefixed_1(pkt, &ecptformatlist)) {
@@ -1283,8 +1283,13 @@
     }
     if (!s->hit) {
         ecpointformats_len = PACKET_remaining(&ecptformatlist);
-        s->session->ext.ecpointformats_len = 0;
+        if (ecpointformats_len == 0) {
+            SSLfatal(s, SSL_AD_DECODE_ERROR,
+                     SSL_F_TLS_PARSE_STOC_EC_PT_FORMATS, SSL_R_BAD_LENGTH);
+            return 0;
+        }
 
+        s->session->ext.ecpointformats_len = 0;
         OPENSSL_free(s->session->ext.ecpointformats);
         s->session->ext.ecpointformats = OPENSSL_malloc(ecpointformats_len);
         if (s->session->ext.ecpointformats == NULL) {

ssl/statem/statem_clnt.c

diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index 8a33386..e79bd7b 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -2452,7 +2452,7 @@
             PACKET sigalgs;
 
             if (!PACKET_get_length_prefixed_2(pkt, &sigalgs)) {
-                SSLfatal(s, SSL_AD_INTERNAL_ERROR,
+                SSLfatal(s, SSL_AD_DECODE_ERROR,
                          SSL_F_TLS_PROCESS_CERTIFICATE_REQUEST,
                          SSL_R_LENGTH_MISMATCH);
                 return MSG_PROCESS_ERROR;
@@ -2484,7 +2484,7 @@
     }
 
     if (PACKET_remaining(pkt) != 0) {
-        SSLfatal(s, SSL_AD_INTERNAL_ERROR,
+        SSLfatal(s, SSL_AD_DECODE_ERROR,
                  SSL_F_TLS_PROCESS_CERTIFICATE_REQUEST,
                  SSL_R_LENGTH_MISMATCH);
         return MSG_PROCESS_ERROR;