| Backport patch to fix CVE-2018-0734. Remove a section which only remove a |
| space. It can't be applied because the context is different. |
| |
| CVE: CVE-2018-0734 |
| Upstream-Status: Backport |
| |
| Signed-off-by: Kai Kang <kai.kang@windriver.com> |
| |
| From 8abfe72e8c1de1b95f50aa0d9134803b4d00070f Mon Sep 17 00:00:00 2001 |
| From: Pauli <paul.dale@oracle.com> |
| Date: Wed, 24 Oct 2018 07:42:46 +1000 |
| Subject: [PATCH] Timing vulnerability in DSA signature generation |
| (CVE-2018-0734). |
| |
| Avoid a timing attack that leaks information via a side channel that |
| triggers when a BN is resized. Increasing the size of the BNs |
| prior to doing anything with them suppresses the attack. |
| |
| Thanks due to Samuel Weiser for finding and locating this. |
| |
| Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de> |
| (Merged from https://github.com/openssl/openssl/pull/7486) |
| |
| (cherry picked from commit a9cfb8c2aa7254a4aa6a1716909e3f8cb78049b6) |
| --- |
| crypto/dsa/dsa_ossl.c | 28 +++++++++++++++------------- |
| 1 file changed, 15 insertions(+), 13 deletions(-) |
| |
| diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c |
| index ca20811200..2dd2d7489a 100644 |
| --- a/crypto/dsa/dsa_ossl.c |
| +++ b/crypto/dsa/dsa_ossl.c |
| @@ -9,6 +9,7 @@ |
| |
| #include <stdio.h> |
| #include "internal/cryptlib.h" |
| +#include "internal/bn_int.h" |
| #include <openssl/bn.h> |
| #include <openssl/sha.h> |
| #include "dsa_locl.h" |
| @@ -180,9 +181,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, |
| { |
| BN_CTX *ctx = NULL; |
| BIGNUM *k, *kinv = NULL, *r = *rp; |
| - BIGNUM *l, *m; |
| + BIGNUM *l; |
| int ret = 0; |
| - int q_bits; |
| + int q_bits, q_words; |
| |
| if (!dsa->p || !dsa->q || !dsa->g) { |
| DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS); |
| @@ -191,8 +192,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, |
| |
| k = BN_new(); |
| l = BN_new(); |
| - m = BN_new(); |
| - if (k == NULL || l == NULL || m == NULL) |
| + if (k == NULL || l == NULL) |
| goto err; |
| |
| if (ctx_in == NULL) { |
| @@ -203,9 +203,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, |
| |
| /* Preallocate space */ |
| q_bits = BN_num_bits(dsa->q); |
| - if (!BN_set_bit(k, q_bits) |
| - || !BN_set_bit(l, q_bits) |
| - || !BN_set_bit(m, q_bits)) |
| + q_words = bn_get_top(dsa->q); |
| + if (!bn_wexpand(k, q_words + 2) |
| + || !bn_wexpand(l, q_words + 2)) |
| goto err; |
| |
| /* Get random k */ |
| @@ -240,14 +240,17 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, |
| * small timing information leakage. We then choose the sum that is |
| * one bit longer than the modulus. |
| * |
| - * TODO: revisit the BN_copy aiming for a memory access agnostic |
| - * conditional copy. |
| + * There are some concerns about the efficacy of doing this. More |
| + * specificly refer to the discussion starting with: |
| + * https://github.com/openssl/openssl/pull/7486#discussion_r228323705 |
| + * The fix is to rework BN so these gymnastics aren't required. |
| */ |
| if (!BN_add(l, k, dsa->q) |
| - || !BN_add(m, l, dsa->q) |
| - || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m)) |
| + || !BN_add(k, l, dsa->q)) |
| goto err; |
| |
| + BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2); |
| + |
| if ((dsa)->meth->bn_mod_exp != NULL) { |
| if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx, |
| dsa->method_mont_p)) |
| @@ -275,7 +278,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, |
| BN_CTX_free(ctx); |
| BN_clear_free(k); |
| BN_clear_free(l); |
| - BN_clear_free(m); |
| return ret; |
| } |
| |
| -- |
| 2.17.0 |
| |