Check SRP parameters early.

Check SRP parameters when they are received so we can send back an
appropriate alert.
Reviewed-by: Kurt Roeckx <kurt@openssl.org>
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 0a006a7..09fe64e 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -1570,6 +1570,12 @@
 		p+=i;
 		n-=param_len;
 
+		if (!srp_verify_server_param(s, &al))
+			{
+			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,SSL_R_BAD_SRP_PARAMETERS);
+			goto f_err;
+			}
+
 /* We must check if there is a certificate */
 #ifndef OPENSSL_NO_RSA
 		if (alg_a & SSL_aRSA)