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Allow (NULL, 0) as a representation of 0

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- We don't check for NULL pointers this deep in the library
- Accessing a NULL pointer when the limb number is 0 as a mistake is the
  very similar to any other out of bounds access
- We could potentially mandate at least 1 limb representation for 0 but
  we either would need to enforce it or the implementation would be less
  robust.
- Allowing zero limb representation - (NULL, 0) in particular - for zero
  is present in the legacy interface, if we disallow it, the
  compatibility code will need to deal with this (more code size and
  opportunities for mistakes)

In summary, interpreting (NULL, 0) as the number zero in the core
interface is the least of the two evils.

Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2022-07-22 14:24:58 +01:00
parent 4670f88991
commit 91dc67d31c
3 changed files with 38 additions and 8 deletions
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12
library/bignum_new.c
View file

@ -190,17 +190,13 @@ static int mpi_core_clear( mbedtls_mpi_uint *X,
size_t nx,
size_t limbs )
{
if( X == NULL )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
else if( nx < limbs )
if( nx < limbs )
return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
else
{
if( X != NULL )
memset( X, 0, nx * ciL );
return( 0 );
}
return( 0 );
}
/* Convert a big-endian byte array aligned to the size of mbedtls_mpi_uint

3
tests/suites/test_suite_mpi.data
View file

@ -82,6 +82,9 @@ mpi_read_write_string:16:"":2:"0":4:0:0
Test mpi_write_string #10 (Negative hex with odd number of digits)
mpi_read_write_string:16:"-1":16:"":3:0:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
Test mbedtls_mpi_core_io functions with null pointers
mbedtls_mpi_core_io_null
Test mbedtls_mpi_core_io_be #1 (Buffer and limbs just fit, input limb-aligned)
mbedtls_mpi_core_io_be:"0941379d00fed1491fe15df284dfde4a142f68aa8d412023195cee66883e6290ffe703f4ea5963bf212713cee46b107c09182b5edcd955adac418bf4918e2889af48e1099d513830cec85c26ac1e158b52620e33ba8692f893efbb2f958b4424":96:12:0:0

31
tests/suites/test_suite_mpi.function
View file

@ -197,6 +197,37 @@ exit:
}
/* END_CASE */
/* BEGIN_CASE */
void mbedtls_mpi_core_io_null()
{
mbedtls_mpi_uint X = 0;
int ret;
ret = mbedtls_mpi_core_read_be( &X, 1, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_write_be( &X, 1, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_read_be( NULL, 0, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_write_be( NULL, 0, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_read_le( &X, 1, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_write_le( &X, 1, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_read_le( NULL, 0, NULL, 0 );
TEST_ASSERT( ret == 0 );
ret = mbedtls_mpi_core_write_le( NULL, 0, NULL, 0 );
TEST_ASSERT( ret == 0 );
exit:
;
}
/* END_CASE */
/* BEGIN_CASE */
void mbedtls_mpi_core_io_be( data_t *input, int nb_int, int nx_64_int, int iret,
int oret )