Try to be more consistent about the alerts we send

We are quite inconsistent about which alerts get sent. Specifically, these
alerts should be used (normally) in the following circumstances:

SSL_AD_DECODE_ERROR = The peer sent a syntactically incorrect message
SSL_AD_ILLEGAL_PARAMETER = The peer sent a message which was syntactically
correct, but a parameter given is invalid for the context
SSL_AD_HANDSHAKE_FAILURE = The peer's messages were syntactically and
semantically correct, but the parameters provided were unacceptable to us
(e.g. because we do not support the requested parameters)
SSL_AD_INTERNAL_ERROR = We messed up (e.g. malloc failure)

The standards themselves aren't always consistent but I think the above
represents the best interpretation.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3480)

ssl/statem/statem_clnt.c

diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index e6a0b35..d4382e8 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -1183,7 +1183,6 @@
 
     /* TLS extensions */
     if (!tls_construct_extensions(s, pkt, SSL_EXT_CLIENT_HELLO, NULL, 0, &al)) {
-        ssl3_send_alert(s, SSL3_AL_FATAL, al);
         SSLerr(SSL_F_TLS_CONSTRUCT_CLIENT_HELLO, ERR_R_INTERNAL_ERROR);
         return 0;
     }
@@ -1928,7 +1927,6 @@
     }
 
     if (!srp_verify_server_param(s, al)) {
-        *al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_SKE_SRP, SSL_R_BAD_SRP_PARAMETERS);
         return 0;
     }
@@ -1987,7 +1985,7 @@
 
     /* test non-zero pubkey */
     if (BN_is_zero(bnpub_key)) {
-        *al = SSL_AD_DECODE_ERROR;
+        *al = SSL_AD_ILLEGAL_PARAMETER;
         SSLerr(SSL_F_TLS_PROCESS_SKE_DHE, SSL_R_BAD_DH_VALUE);
         goto err;
     }
@@ -2000,7 +1998,7 @@
     p = g = NULL;
 
     if (DH_check_params(dh, &check_bits) == 0 || check_bits != 0) {
-        *al = SSL_AD_DECODE_ERROR;
+        *al = SSL_AD_ILLEGAL_PARAMETER;
         SSLerr(SSL_F_TLS_PROCESS_SKE_DHE, SSL_R_BAD_DH_VALUE);
         goto err;
     }
@@ -2075,7 +2073,7 @@
      * invalid curve. ECParameters is 3 bytes.
      */
     if (!tls1_check_curve(s, ecparams, 3)) {
-        *al = SSL_AD_DECODE_ERROR;
+        *al = SSL_AD_ILLEGAL_PARAMETER;
         SSLerr(SSL_F_TLS_PROCESS_SKE_ECDHE, SSL_R_WRONG_CURVE);
         return 0;
     }
@@ -2124,7 +2122,7 @@
     if (!EVP_PKEY_set1_tls_encodedpoint(s->s3->peer_tmp,
                                         PACKET_data(&encoded_pt),
                                         PACKET_remaining(&encoded_pt))) {
-        *al = SSL_AD_DECODE_ERROR;
+        *al = SSL_AD_ILLEGAL_PARAMETER;
         SSLerr(SSL_F_TLS_PROCESS_SKE_ECDHE, SSL_R_BAD_ECPOINT);
         return 0;
     }
@@ -2201,7 +2199,7 @@
         if (!PACKET_get_sub_packet(&save_param_start, &params,
                                    PACKET_remaining(&save_param_start) -
                                    PACKET_remaining(pkt))) {
-            al = SSL_AD_INTERNAL_ERROR;
+            al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_TLS_PROCESS_KEY_EXCHANGE, ERR_R_INTERNAL_ERROR);
             goto err;
         }
@@ -2750,7 +2748,7 @@
     identitylen = strlen(identity);
     if (identitylen > PSK_MAX_IDENTITY_LEN) {
         SSLerr(SSL_F_TLS_CONSTRUCT_CKE_PSK_PREAMBLE, ERR_R_INTERNAL_ERROR);
-        *al = SSL_AD_HANDSHAKE_FAILURE;
+        *al = SSL_AD_INTERNAL_ERROR;
         goto err;
     }
 
@@ -3137,7 +3135,7 @@
         if (!tls_construct_cke_srp(s, pkt, &al))
             goto err;
     } else if (!(alg_k & SSL_kPSK)) {
-        ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+        ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
         SSLerr(SSL_F_TLS_CONSTRUCT_CLIENT_KEY_EXCHANGE, ERR_R_INTERNAL_ERROR);
         goto err;
     }