Fix verify loop with CRL checking.

PR #3090
Reported by: Franck Youssef <fry@open.ch>

If no new reason codes are obtained after checking a CRL exit with an
error to avoid repeatedly checking the same CRL.

This will only happen if verify errors such as invalid CRL scope are
overridden in a callback.

crypto/x509/x509_vfy.c

@@ -838,6 +838,7 @@ static int check_cert(X509_STORE_CTX *ctx)
 	X509_CRL *crl = NULL, *dcrl = NULL;
 	X509 *x;
 	int ok, cnum;
+	unsigned int last_reasons;
 	cnum = ctx->error_depth;
 	x = sk_X509_value(ctx->chain, cnum);
 	ctx->current_cert = x;
@@ -846,6 +847,7 @@ static int check_cert(X509_STORE_CTX *ctx)
 	ctx->current_reasons = 0;
 	while (ctx->current_reasons != CRLDP_ALL_REASONS)
 		{
+		last_reasons = ctx->current_reasons;
 		/* Try to retrieve relevant CRL */
 		if (ctx->get_crl)
 			ok = ctx->get_crl(ctx, &crl, x);
@@ -889,6 +891,15 @@ static int check_cert(X509_STORE_CTX *ctx)
 		X509_CRL_free(dcrl);
 		crl = NULL;
 		dcrl = NULL;
+		/* If reasons not updated we wont get anywhere by
+		 * another iteration, so exit loop.
+		 */
+		if (last_reasons == ctx->current_reasons)
+			{
+			ctx->error = X509_V_ERR_UNABLE_TO_GET_CRL;
+			ok = ctx->verify_cb(0, ctx);
+			goto err;
+			}
 		}
 	err:
 	X509_CRL_free(crl);