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psa_export_key: zero out potential garbage in the output buffer

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In psa_export_key, ensure that each byte of the output buffer either
contains its original value, is zero, or is part of the actual output.
Specifically, don't risk having partial output on error, and don't
leave extra data at the end of the buffer when exporting an asymmetric
key.

Test that exporting to a previously zeroed buffer leaves the buffer
zeroed outside the actual output if any.
This commit is contained in:
Gilles Peskine 2018-06-20 00:11:45 +02:00 committed by itayzafrir
parent 0e2315859f
commit e66ca3bbf3
2 changed files with 29 additions and 0 deletions
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5
library/psa_crypto.c
View File

@ -628,17 +628,22 @@ static psa_status_t psa_internal_export_key( psa_key_slot_t key,
else
ret = mbedtls_pk_write_key_der( &pk, data, data_size );
if( ret < 0 )
{
memset( data, 0, data_size );
return( mbedtls_to_psa_error( ret ) );
}
/* The mbedtls_pk_xxx functions write to the end of the buffer.
* Move the data to the beginning and erase remaining data
* at the original location. */
if( 2 * (size_t) ret <= data_size )
{
memcpy( data, data + data_size - ret, ret );
memset( data + data_size - ret, 0, ret );
}
else if( (size_t) ret < data_size )
{
memmove( data, data + data_size - ret, ret );
memset( data + ret, 0, data_size - ret );
}
*data_length = ret;
return( PSA_SUCCESS );

24
tests/suites/test_suite_psa_crypto.function
View File

@ -7,6 +7,25 @@
#else
#define PSA_CRYPTO_TEST_SIZE_T_RANGE( x ) 1
#endif
/** Test if a buffer is not all-bits zero.
*
* \param buffer Pointer to the beginning of the buffer.
* \param size Size of the buffer in bytes.
*
* \return 0 if the buffer is all-bits-zero.
* \return A nonzero value otherwise.
*/
int mem_is_nonzero( void *buffer, size_t size )
{
size_t i;
for( i = 0; i < size; i++ )
{
if( ( (unsigned char *) buffer )[i] != 0 )
return( i + 1 );
}
return( 0 );
}
/* END_HEADER */
/* BEGIN_DEPENDENCIES
@ -106,8 +125,13 @@ void import_export( data_t *data,
exported, export_size,
&exported_length );
TEST_ASSERT( status == (psa_status_t) expected_export_status );
TEST_ASSERT( ! mem_is_nonzero( exported + exported_length,
export_size - exported_length ) );
if( status != PSA_SUCCESS )
{
TEST_ASSERT( exported_length == 0 );
goto destroy;
}
if( canonical_input )
{