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>

1 files changed, 34 insertions, 9 deletions

diff --git a/ssl/tls_srp.c b/ssl/tls_srp.c
index c363fc309c..1aa90c5307 100644
--- a/ssl/tls_srp.c
+++ b/ssl/tls_srp.c
@@ -410,16 +410,45 @@ err:
 	return ret;
 	}
 
-int SRP_Calc_A_param(SSL *s)
+int srp_verify_server_param(SSL *s, int *al)
 	{
-	unsigned char rnd[SSL_MAX_MASTER_KEY_LENGTH];
+	SRP_CTX *srp = &s->srp_ctx;
+	/* Sanity check parameters: we can quickly check B % N == 0
+	 * by checking B != 0 since B < N
+	 */
+	if (BN_ucmp(srp->g, srp->N) >=0 || BN_ucmp(srp->B, srp->N) >= 0
+		|| BN_is_zero(srp->B))
+		{
+		*al = SSL3_AD_ILLEGAL_PARAMETER;
+		return 0;
+		}
 
-	if (BN_num_bits(s->srp_ctx.N) < s->srp_ctx.strength)
+	if (BN_num_bits(srp->N) < srp->strength)
+		{
+		*al = TLS1_AD_INSUFFICIENT_SECURITY;
 		return 0;
+		}
 
-	if (s->srp_ctx.SRP_verify_param_callback ==NULL && 
-		!SRP_check_known_gN_param(s->srp_ctx.g,s->srp_ctx.N))
+	if (srp->SRP_verify_param_callback)
+		{
+		if (srp->SRP_verify_param_callback(s, srp->SRP_cb_arg) <= 0)
+			{
+			*al = TLS1_AD_INSUFFICIENT_SECURITY;
+			return 0;
+			}
+		}
+	else if(!SRP_check_known_gN_param(srp->g, srp->N))
+		{
+		*al = TLS1_AD_INSUFFICIENT_SECURITY;
 		return 0;
+		}
+
+	return 1;
+	}
+
+int SRP_Calc_A_param(SSL *s)
+	{
+	unsigned char rnd[SSL_MAX_MASTER_KEY_LENGTH];
 
 	if (RAND_bytes(rnd, sizeof(rnd)) <= 0)
 		return 0;
@@ -429,10 +458,6 @@ int SRP_Calc_A_param(SSL *s)
 	if (!(s->srp_ctx.A = SRP_Calc_A(s->srp_ctx.a,s->srp_ctx.N,s->srp_ctx.g)))
 		return 0;
 
-	/* We can have a callback to verify SRP param!! */
-	if (s->srp_ctx.SRP_verify_param_callback !=NULL) 
-		return s->srp_ctx.SRP_verify_param_callback(s,s->srp_ctx.SRP_cb_arg);
-
 	return 1;
 	}