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Fix NULL pointer dereference for BN_mod_exp2_mont

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This fixes a bug whereby BN_mod_exp2_mont can dereference a NULL pointer
if BIGNUM argument m represents zero.

Regression test added. Fixes #17648.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17783)
This commit is contained in:
Hugo Landau 2022-03-01 14:08:12 +00:00 committed by Tomas Mraz
parent df5c86e9f8
commit 43135a5d22
2 changed files with 46 additions and 1 deletions
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2
crypto/bn/bn_exp2.c
View File

@ -32,7 +32,7 @@ int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,
bn_check_top(p2);
bn_check_top(m);
if (!(m->d[0] & 1)) {
if (!BN_is_odd(m)) {
ERR_raise(ERR_LIB_BN, BN_R_CALLED_WITH_EVEN_MODULUS);
return 0;
}

45
test/bntest.c
View File

@ -3012,6 +3012,50 @@ static int test_mod_exp_consttime(int i)
return res;
}
/*
* Regression test to ensure BN_mod_exp2_mont fails safely if argument m is
* zero.
*/
static int test_mod_exp2_mont(void)
{
int res = 0;
BIGNUM *exp_result = NULL;
BIGNUM *exp_a1 = NULL, *exp_p1 = NULL, *exp_a2 = NULL, *exp_p2 = NULL,
*exp_m = NULL;
if (!TEST_ptr(exp_result = BN_new())
|| !TEST_ptr(exp_a1 = BN_new())
|| !TEST_ptr(exp_p1 = BN_new())
|| !TEST_ptr(exp_a2 = BN_new())
|| !TEST_ptr(exp_p2 = BN_new())
|| !TEST_ptr(exp_m = BN_new()))
goto err;
if (!TEST_true(BN_one(exp_a1))
|| !TEST_true(BN_one(exp_p1))
|| !TEST_true(BN_one(exp_a2))
|| !TEST_true(BN_one(exp_p2)))
goto err;
BN_zero(exp_m);
/* input of 0 is even, so must fail */
if (!TEST_int_eq(BN_mod_exp2_mont(exp_result, exp_a1, exp_p1, exp_a2,
exp_p2, exp_m, ctx, NULL), 0))
goto err;
res = 1;
err:
BN_free(exp_result);
BN_free(exp_a1);
BN_free(exp_p1);
BN_free(exp_a2);
BN_free(exp_p2);
BN_free(exp_m);
return res;
}
static int file_test_run(STANZA *s)
{
static const FILETEST filetests[] = {
@ -3154,6 +3198,7 @@ int setup_tests(void)
ADD_TEST(test_gcd_prime);
ADD_ALL_TESTS(test_mod_exp, (int)OSSL_NELEM(ModExpTests));
ADD_ALL_TESTS(test_mod_exp_consttime, (int)OSSL_NELEM(ModExpTests));
ADD_TEST(test_mod_exp2_mont);
if (stochastic)
ADD_TEST(test_rand_range);
} else {