mirror/mbedtls
1
0
Fork 0
mirror of https://github.com/Mbed-TLS/mbedtls.git synced 2025-01-18 19:27:41 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Fix undefined behavior with the most negative mbedtls_mpi_sint

Browse Source 
When x is the most negative value of a two's complement type,
`(unsigned_type)(-x)` has undefined behavior, whereas `-(unsigned_type)x`
has well-defined behavior and does what was intended.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-11-15 23:02:14 +01:00
parent db14a9d180
commit af601f9751
4 changed files with 156 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
ChangeLog.d/mpi-most-negative-sint.txt Normal file
View File

@ -0,0 +1,4 @@
Bugfix
* Fix undefined behavior (typically harmless in practice) when some bignum
functions receive the most negative value of mbedtls_mpi_sint. Credit
to OSS-Fuzz. Fixes #6597.

10
library/bignum.c
View File

@ -263,7 +263,7 @@ int mbedtls_mpi_lset( mbedtls_mpi *X, mbedtls_mpi_sint z )
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, 1 ) );
memset( X->p, 0, X->n * ciL );
X->p[0] = ( z < 0 ) ? -z : z;
X->p[0] = ( z < 0 ) ? -(mbedtls_mpi_uint)z : z;
X->s = ( z < 0 ) ? -1 : 1;
cleanup:
@ -853,7 +853,7 @@ int mbedtls_mpi_cmp_int( const mbedtls_mpi *X, mbedtls_mpi_sint z )
mbedtls_mpi_uint p[1];
MPI_VALIDATE_RET( X != NULL );
*p = ( z < 0 ) ? -z : z;
*p = ( z < 0 ) ? -(mbedtls_mpi_uint)z : z;
Y.s = ( z < 0 ) ? -1 : 1;
Y.n = 1;
Y.p = p;
@ -1057,7 +1057,7 @@ int mbedtls_mpi_add_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1075,7 +1075,7 @@ int mbedtls_mpi_sub_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1413,7 +1413,7 @@ int mbedtls_mpi_div_int( mbedtls_mpi *Q, mbedtls_mpi *R,
mbedtls_mpi_uint p[1];
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;

144
tests/suites/test_suite_bignum.function
View File

@ -1447,6 +1447,150 @@ exit:
}
/* END_CASE */
/* BEGIN_CASE */
void most_negative_mpi_sint( )
{
/* Ad hoc tests for n = -p = -2^(biL-1) as a mbedtls_mpi_sint. We
* guarantee that mbedtls_mpi_sint is a two's complement type, so this
* is a valid value. However, negating it (`-n`) has undefined behavior
* (although in practice `-n` evaluates to the value n).
*
* This function has ad hoc tests for this value. It's separated from other
* functions because the test framework makes it hard to pass this value
* into test cases.
*
* In the comments here:
* - biL = number of bits in limbs
* - p = 2^(biL-1) (smallest positive value not in mbedtls_mpi_sint range)
* - n = -2^(biL-1) (largest negative value in mbedtls_mpi_sint range)
*/
mbedtls_mpi A, R, X;
mbedtls_mpi_init( &A );
mbedtls_mpi_init( &R );
mbedtls_mpi_init( &X );
const size_t biL = 8 * sizeof( mbedtls_mpi_sint );
mbedtls_mpi_uint most_positive_plus_1 = (mbedtls_mpi_uint) 1 << ( biL - 1 );
const mbedtls_mpi_sint most_positive = most_positive_plus_1 - 1;
const mbedtls_mpi_sint most_negative = - most_positive - 1;
TEST_EQUAL( (mbedtls_mpi_uint) most_negative,
(mbedtls_mpi_uint) 1 << ( biL - 1 ) );
TEST_EQUAL( (mbedtls_mpi_uint) most_negative << 1, 0 );
/* Test mbedtls_mpi_lset() */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_negative ), 0 );
TEST_EQUAL( A.s, -1 );
TEST_EQUAL( A.n, 1 );
TEST_EQUAL( A.p[0], most_positive_plus_1 );
/* Test mbedtls_mpi_cmp_int(): -p == -p */
TEST_EQUAL( mbedtls_mpi_cmp_int( &A, most_negative ), 0 );
/* Test mbedtls_mpi_cmp_int(): -(p+1) < -p */
A.p[0] = most_positive_plus_1 + 1;
TEST_EQUAL( mbedtls_mpi_cmp_int( &A, most_negative ), -1 );
/* Test mbedtls_mpi_cmp_int(): -(p-1) > -p */
A.p[0] = most_positive_plus_1 - 1;
TEST_EQUAL( mbedtls_mpi_cmp_int( &A, most_negative ), 1 );
/* Test mbedtls_mpi_add_int(): (p-1) + (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_positive ), 0 );
TEST_EQUAL( mbedtls_mpi_add_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, -1 ), 0 );
/* Test mbedtls_mpi_add_int(): (0) + (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, 0 ), 0 );
TEST_EQUAL( mbedtls_mpi_add_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, most_negative ), 0 );
/* Test mbedtls_mpi_add_int(): (-p) + (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_add_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( X.s, -1 );
TEST_EQUAL( X.n, 2 );
TEST_EQUAL( X.p[0], 0 );
TEST_EQUAL( X.p[1], 1 );
/* Test mbedtls_mpi_sub_int(): (p) - (-p) */
mbedtls_mpi_free( &X );
TEST_EQUAL( mbedtls_mpi_lset( &A, most_positive ), 0 );
TEST_EQUAL( mbedtls_mpi_sub_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( X.s, 1 );
TEST_EQUAL( X.n, 1 );
TEST_EQUAL( X.p[0], ~(mbedtls_mpi_uint)0 );
/* Test mbedtls_mpi_sub_int(): (0) - (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, 0 ), 0 );
TEST_EQUAL( mbedtls_mpi_sub_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( X.s, 1 );
TEST_EQUAL( X.n, 1 );
TEST_EQUAL( X.p[0], most_positive_plus_1 );
/* Test mbedtls_mpi_sub_int(): (-p) - (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_sub_int( &X, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 0 ), 0 );
/* Test mbedtls_mpi_div_int(): (-p+1) / (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, -most_positive ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 0 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, -most_positive ), 0 );
/* Test mbedtls_mpi_div_int(): (-p) / (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, 0 ), 0 );
/* Test mbedtls_mpi_div_int(): (-2*p) / (-p) */
TEST_EQUAL( mbedtls_mpi_shift_l( &A, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 2 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, 0 ), 0 );
/* Test mbedtls_mpi_div_int(): (-2*p+1) / (-p) */
TEST_EQUAL( mbedtls_mpi_add_int( &A, &A, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, -most_positive ), 0 );
/* Test mbedtls_mpi_div_int(): (p-1) / (-p) */
TEST_EQUAL( mbedtls_mpi_lset( &A, most_positive ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, 0 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, most_positive ), 0 );
/* Test mbedtls_mpi_div_int(): (p) / (-p) */
TEST_EQUAL( mbedtls_mpi_add_int( &A, &A, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, -1 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, 0 ), 0 );
/* Test mbedtls_mpi_div_int(): (2*p) / (-p) */
TEST_EQUAL( mbedtls_mpi_shift_l( &A, 1 ), 0 );
TEST_EQUAL( mbedtls_mpi_div_int( &X, &R, &A, most_negative ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &X, -2 ), 0 );
TEST_EQUAL( mbedtls_mpi_cmp_int( &R, 0 ), 0 );
/* Test mbedtls_mpi_mod_int(): never valid */
TEST_EQUAL( mbedtls_mpi_mod_int( X.p, &A, most_negative ),
MBEDTLS_ERR_MPI_NEGATIVE_VALUE );
/* Test mbedtls_mpi_random(): never valid */
TEST_EQUAL( mbedtls_mpi_random( &X, most_negative, &A,
mbedtls_test_rnd_std_rand, NULL ),
MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
exit:
mbedtls_mpi_free( &A );
mbedtls_mpi_free( &R );
mbedtls_mpi_free( &X );
}
/* END_CASE */
/* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
void mpi_selftest( )
{

3
tests/suites/test_suite_bignum.misc.data
View File

@ -1934,6 +1934,9 @@ mpi_random_fail:2:"01":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
MPI random bad arguments: min > N = 1, 0 limb in upper bound
mpi_random_fail:2:"000000000000000001":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Most negative mbedtls_mpi_sint
most_negative_mpi_sint:
MPI Selftest
depends_on:MBEDTLS_SELF_TEST
mpi_selftest: