From 43135a5d2274c24e97f50e16ce492c22eb717ab2 Mon Sep 17 00:00:00 2001 From: Hugo Landau Date: Tue, 1 Mar 2022 14:08:12 +0000 Subject: [PATCH] Fix NULL pointer dereference for BN_mod_exp2_mont 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 Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/17783) --- crypto/bn/bn_exp2.c | 2 +- test/bntest.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 46 insertions(+), 1 deletion(-) diff --git a/crypto/bn/bn_exp2.c b/crypto/bn/bn_exp2.c index 4713503d07..e8043cb26f 100644 --- a/crypto/bn/bn_exp2.c +++ b/crypto/bn/bn_exp2.c @@ -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; } diff --git a/test/bntest.c b/test/bntest.c index efdb3ef963..f129c71ab8 100644 --- a/test/bntest.c +++ b/test/bntest.c @@ -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 { -- GitLab