CVE: CVE-2018-0735

Upstream-Status: Backport

Signed-off-by: Kai Kang <kai.kang@windriver.com>

From b1d6d55ece1c26fa2829e2b819b038d7b6d692b4 Mon Sep 17 00:00:00 2001
From: Pauli <paul.dale@oracle.com>
Date: Fri, 26 Oct 2018 10:54:58 +1000
Subject: [PATCH] Timing vulnerability in ECDSA signature generation
 (CVE-2018-0735)

Preallocate an extra limb for some of the big numbers to avoid a reallocation
that can potentially provide a side channel.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/7486)

(cherry picked from commit 99540ec79491f59ed8b46b4edf130e17dc907f52)
---
 crypto/ec/ec_mult.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/crypto/ec/ec_mult.c b/crypto/ec/ec_mult.c
index 7e1b3650e7..0e0a5e1394 100644
--- a/crypto/ec/ec_mult.c
+++ b/crypto/ec/ec_mult.c
@@ -206,8 +206,8 @@ int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r,
      */
     cardinality_bits = BN_num_bits(cardinality);
     group_top = bn_get_top(cardinality);
-    if ((bn_wexpand(k, group_top + 1) == NULL)
-        || (bn_wexpand(lambda, group_top + 1) == NULL)) {
+    if ((bn_wexpand(k, group_top + 2) == NULL)
+        || (bn_wexpand(lambda, group_top + 2) == NULL)) {
         ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
         goto err;
     }
@@ -244,7 +244,7 @@ int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r,
      * k := scalar + 2*cardinality
      */
     kbit = BN_is_bit_set(lambda, cardinality_bits);
-    BN_consttime_swap(kbit, k, lambda, group_top + 1);
+    BN_consttime_swap(kbit, k, lambda, group_top + 2);
 
     group_top = bn_get_top(group->field);
     if ((bn_wexpand(s->X, group_top) == NULL)
-- 
2.17.0