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bn: Properly error out if aliasing return value with modulus

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Test case amended from code initially written by Bernd Edlinger.

Fixes #21110

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22421)
This commit is contained in:
Tomas Mraz 2023-10-18 15:50:30 +02:00 committed by Hugo Landau
parent 62f8606a0a
commit af0025fc40
5 changed files with 145 additions and 1 deletions
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21
crypto/bn/bn_exp.c
View File

@ -242,6 +242,14 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
wstart = bits - 1; /* The top bit of the window */
wend = 0; /* The bottom bit of the window */
if (r == p) {
BIGNUM *p_dup = BN_CTX_get(ctx);
if (p_dup == NULL || BN_copy(p_dup, p) == NULL)
goto err;
p = p_dup;
}
if (!BN_one(r))
goto err;
@ -1317,6 +1325,11 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
return 0;
}
if (r == m) {
ERR_raise(ERR_LIB_BN, ERR_R_PASSED_INVALID_ARGUMENT);
return 0;
}
bits = BN_num_bits(p);
if (bits == 0) {
/* x**0 mod 1, or x**0 mod -1 is still zero. */
@ -1361,6 +1374,14 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
wstart = bits - 1; /* The top bit of the window */
wend = 0; /* The bottom bit of the window */
if (r == p) {
BIGNUM *p_dup = BN_CTX_get(ctx);
if (p_dup == NULL || BN_copy(p_dup, p) == NULL)
goto err;
p = p_dup;
}
if (!BN_one(r))
goto err;

10
crypto/bn/bn_mod.c
View File

@ -17,6 +17,11 @@ int BN_nnmod(BIGNUM *r, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)
* always holds)
*/
if (r == d) {
ERR_raise(ERR_LIB_BN, ERR_R_PASSED_INVALID_ARGUMENT);
return 0;
}
if (!(BN_mod(r, m, d, ctx)))
return 0;
if (!r->neg)
@ -184,6 +189,11 @@ int bn_mod_sub_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
const BIGNUM *m)
{
if (r == m) {
ERR_raise(ERR_LIB_BN, ERR_R_PASSED_INVALID_ARGUMENT);
return 0;
}
if (!BN_sub(r, a, b))
return 0;
if (r->neg)

5
doc/man3/BN_add.pod
View File

@ -114,6 +114,11 @@ temporary variables; see L<BN_CTX_new(3)>.
Unless noted otherwise, the result B<BIGNUM> must be different from
the arguments.
=head1 NOTES
For modular operations such as BN_nnmod() or BN_mod_exp() it is an error
to use the same B<BIGNUM> object for the modulus as for the output.
=head1 RETURN VALUES
The BN_mod_sqrt() returns the result (possibly incorrect if I<p> is

6
doc/man3/BN_mod_inverse.pod
View File

@ -18,7 +18,11 @@ places the result in B<r> (C<(a*r)%n==1>). If B<r> is NULL,
a new B<BIGNUM> is created.
B<ctx> is a previously allocated B<BN_CTX> used for temporary
variables. B<r> may be the same B<BIGNUM> as B<a> or B<n>.
variables. B<r> may be the same B<BIGNUM> as B<a>.
=head1 NOTES
It is an error to use the same B<BIGNUM> as B<n>.
=head1 RETURN VALUES

104
test/bntest.c
View File

@ -3165,6 +3165,108 @@ err:
return res;
}
static int test_mod_inverse(void)
{
int res = 0;
char *str = NULL;
BIGNUM *a = NULL;
BIGNUM *b = NULL;
BIGNUM *r = NULL;
if (!TEST_true(BN_dec2bn(&a, "5193817943")))
goto err;
if (!TEST_true(BN_dec2bn(&b, "3259122431")))
goto err;
if (!TEST_ptr(r = BN_new()))
goto err;
if (!TEST_ptr_eq(BN_mod_inverse(r, a, b, ctx), r))
goto err;
if (!TEST_ptr_ne(str = BN_bn2dec(r), NULL))
goto err;
if (!TEST_int_eq(strcmp(str, "2609653924"), 0))
goto err;
/* Note that this aliases the result with the modulus. */
if (!TEST_ptr_null(BN_mod_inverse(b, a, b, ctx)))
goto err;
res = 1;
err:
BN_free(a);
BN_free(b);
BN_free(r);
OPENSSL_free(str);
return res;
}
static int test_mod_exp_alias(int idx)
{
int res = 0;
char *str = NULL;
BIGNUM *a = NULL;
BIGNUM *b = NULL;
BIGNUM *c = NULL;
BIGNUM *r = NULL;
if (!TEST_true(BN_dec2bn(&a, "15")))
goto err;
if (!TEST_true(BN_dec2bn(&b, "10")))
goto err;
if (!TEST_true(BN_dec2bn(&c, "39")))
goto err;
if (!TEST_ptr(r = BN_new()))
goto err;
if (!TEST_int_eq((idx == 0 ? BN_mod_exp_simple
: BN_mod_exp_recp)(r, a, b, c, ctx), 1))
goto err;
if (!TEST_ptr_ne(str = BN_bn2dec(r), NULL))
goto err;
if (!TEST_str_eq(str, "36"))
goto err;
OPENSSL_free(str);
str = NULL;
BN_copy(r, b);
/* Aliasing with exponent must work. */
if (!TEST_int_eq((idx == 0 ? BN_mod_exp_simple
: BN_mod_exp_recp)(r, a, r, c, ctx), 1))
goto err;
if (!TEST_ptr_ne(str = BN_bn2dec(r), NULL))
goto err;
if (!TEST_str_eq(str, "36"))
goto err;
OPENSSL_free(str);
str = NULL;
/* Aliasing with modulus should return failure for the simple call. */
if (idx == 0) {
if (!TEST_int_eq(BN_mod_exp_simple(c, a, b, c, ctx), 0))
goto err;
} else {
if (!TEST_int_eq(BN_mod_exp_recp(c, a, b, c, ctx), 1))
goto err;
if (!TEST_ptr_ne(str = BN_bn2dec(c), NULL))
goto err;
if (!TEST_str_eq(str, "36"))
goto err;
}
res = 1;
err:
BN_free(a);
BN_free(b);
BN_free(c);
BN_free(r);
OPENSSL_free(str);
return res;
}
static int file_test_run(STANZA *s)
{
static const FILETEST filetests[] = {
@ -3274,6 +3376,8 @@ int setup_tests(void)
ADD_ALL_TESTS(test_signed_mod_replace_ab, OSSL_NELEM(signed_mod_tests));
ADD_ALL_TESTS(test_signed_mod_replace_ba, OSSL_NELEM(signed_mod_tests));
ADD_TEST(test_mod);
ADD_TEST(test_mod_inverse);
ADD_ALL_TESTS(test_mod_exp_alias, 2);
ADD_TEST(test_modexp_mont5);
ADD_TEST(test_kronecker);
ADD_TEST(test_rand);