Don't check curves that haven't been sent

Don't check that the curve appears in the list of acceptable curves for the
peer, if they didn't send us such a list (RFC 4492 does not require that the
extension be sent).

Reviewed-by: Emilia Käsper <emilia@openssl.org>
(cherry picked from commit b79d24101e3b5904b3770d60e32bdd6edc558337)

1 files changed, 10 insertions, 0 deletions

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index a59fe82e1f..3e01b6af6a 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -763,6 +763,16 @@ static int tls1_check_ec_key(SSL *s,
     for (j = 0; j <= 1; j++) {
         if (!tls1_get_curvelist(s, j, &pcurves, &num_curves))
             return 0;
+        if (j == 1 && num_curves == 0) {
+            /*
+             * If we've not received any curves then skip this check.
+             * RFC 4492 does not require the supported elliptic curves extension
+             * so if it is not sent we can just choose any curve.
+             * It is invalid to send an empty list in the elliptic curves
+             * extension, so num_curves == 0 always means no extension.
+             */
+            break;
+        }
         for (i = 0; i < num_curves; i++, pcurves += 2) {
             if (pcurves[0] == curve_id[0] && pcurves[1] == curve_id[1])
                 break;