git.openwrt.org Git - openwrt/staging/mans0n.git/blob

   1 From c93461c1d98f52681717a088776ab32fd97872b0 Mon Sep 17 00:00:00 2001
   2 From: Jouni Malinen <jouni@codeaurora.org>
   3 Date: Fri, 8 Mar 2019 00:24:12 +0200
   4 Subject: [PATCH 03/14] OpenSSL: Use constant time selection for
   5  crypto_bignum_legendre()
   6
   7 Get rid of the branches that depend on the result of the Legendre
   8 operation. This is needed to avoid leaking information about different
   9 temporary results in blinding mechanisms.
  10
  11 This is related to CVE-2019-9494 and CVE-2019-9495.
  12
  13 Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
  14 ---
  15  src/crypto/crypto_openssl.c | 15 +++++++++------
  16  1 file changed, 9 insertions(+), 6 deletions(-)
  17
  18 --- a/src/crypto/crypto_openssl.c
  19 +++ b/src/crypto/crypto_openssl.c
  20 @@ -24,6 +24,7 @@
  21  #endif /* CONFIG_ECC */
  22
  23  #include "common.h"
  24 +#include "utils/const_time.h"
  25  #include "wpabuf.h"
  26  #include "dh_group5.h"
  27  #include "sha1.h"
  28 @@ -1435,6 +1436,7 @@ int crypto_bignum_legendre(const struct
  29         BN_CTX *bnctx;
  30         BIGNUM *exp = NULL, *tmp = NULL;
  31         int res = -2;
  32 +       unsigned int mask;
  33
  34         if (TEST_FAIL())
  35                 return -2;
  36 @@ -1453,12 +1455,13 @@ int crypto_bignum_legendre(const struct
  37                                        (const BIGNUM *) p, bnctx, NULL))
  38                 goto fail;
  39
  40 -       if (BN_is_word(tmp, 1))
  41 -               res = 1;
  42 -       else if (BN_is_zero(tmp))
  43 -               res = 0;
  44 -       else
  45 -               res = -1;
  46 +       /* Return 1 if tmp == 1, 0 if tmp == 0, or -1 otherwise. Need to use
  47 +        * constant time selection to avoid branches here. */
  48 +       res = -1;
  49 +       mask = const_time_eq(BN_is_word(tmp, 1), 1);
  50 +       res = const_time_select_int(mask, 1, res);
  51 +       mask = const_time_eq(BN_is_zero(tmp), 1);
  52 +       res = const_time_select_int(mask, 0, res);
  53
  54  fail:
  55         BN_clear_free(tmp);