File openssl-CVE-2018-0734.patch of Package openssl-1_1.20902

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File openssl-CVE-2018-0734.patch of Package openssl-1_1.20902

commit ef11e19d1365eea2b1851e6f540a0bf365d303e7
Author: Pauli <paul.dale@oracle.com>
Date:   Wed Oct 24 07:42:46 2018 +1000

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)

Index: openssl-1.1.0i/crypto/dsa/dsa_ossl.c
===================================================================
--- openssl-1.1.0i.orig/crypto/dsa/dsa_ossl.c	2018-11-05 12:00:07.053658627 +0100
+++ openssl-1.1.0i/crypto/dsa/dsa_ossl.c	2018-11-05 12:00:11.253681776 +0100
@@ -11,6 +11,7 @@
 
 #include <stdio.h>
 #include "internal/cryptlib.h"
+#include "internal/bn_int.h"
 #include <openssl/bn.h>
 #include <openssl/sha.h>
 #include "dsa_locl.h"
@@ -196,9 +197,9 @@ static int dsa_sign_setup(DSA *dsa, BN_C
 {
     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);
@@ -207,8 +208,7 @@ static int dsa_sign_setup(DSA *dsa, BN_C
 
     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) {
@@ -219,9 +219,9 @@ static int dsa_sign_setup(DSA *dsa, BN_C
 
     /* 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 */
@@ -256,14 +256,17 @@ static int dsa_sign_setup(DSA *dsa, BN_C
      * 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))
@@ -291,7 +294,6 @@ static int dsa_sign_setup(DSA *dsa, BN_C
         BN_CTX_free(ctx);
     BN_clear_free(k);
     BN_clear_free(l);
-    BN_clear_free(m);
     return ret;
 }

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