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HMAC: improve robustness checks on hash/block size

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In psa_mac_setup and psa_hmac_setup_internal, perform a sanity check
on the hash size and the hash block size respectively. These sanity
checks should only trigger on an incompletely or incorrectly
implemented hash function.

Remove the check on the block size in psa_hmac_finish_internal
because at this point it has already been checked and used.
This commit is contained in:
Gilles Peskine 2018-07-16 00:36:29 +02:00 committed by itayzafrir
parent 1e6bfdff5e
commit 9aa369eafb
1 changed files with 23 additions and 5 deletions
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28
library/psa_crypto.c
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@ -1418,10 +1418,21 @@ static psa_status_t psa_hmac_setup_internal( psa_hmac_internal_data *hmac,
{ {
unsigned char ipad[PSA_HMAC_MAX_HASH_BLOCK_SIZE]; unsigned char ipad[PSA_HMAC_MAX_HASH_BLOCK_SIZE];
size_t i; size_t i;
size_t hash_size = PSA_HASH_SIZE( hash_alg );
size_t block_size = psa_get_hash_block_size( hash_alg ); size_t block_size = psa_get_hash_block_size( hash_alg );
psa_status_t status; psa_status_t status;
if( block_size == 0 ) /* Sanity checks on block_size, to guarantee that there won't be a buffer
* overflow below. This should never trigger if the hash algorithm
* is implemented correctly. */
/* The size checks against the ipad and opad buffers cannot be written
* `block_size > sizeof( ipad ) || block_size > sizeof( hmac->opad )`
* because that triggers -Wlogical-op on GCC 7.3. */
if( block_size > sizeof( ipad ) )
return( PSA_ERROR_NOT_SUPPORTED );
if( block_size > sizeof( hmac->opad ) )
return( PSA_ERROR_NOT_SUPPORTED );
if( block_size < hash_size )
return( PSA_ERROR_NOT_SUPPORTED ); return( PSA_ERROR_NOT_SUPPORTED );
if( key_length > block_size ) if( key_length > block_size )
@ -1517,16 +1528,26 @@ static psa_status_t psa_mac_setup( psa_mac_operation_t *operation,
status = PSA_ERROR_NOT_SUPPORTED; status = PSA_ERROR_NOT_SUPPORTED;
goto exit; goto exit;
} }
operation->mac_size = PSA_HASH_SIZE( hash_alg );
/* Sanity check. This shouldn't fail on a valid configuration. */
if( operation->mac_size == 0 ||
operation->mac_size > sizeof( operation->ctx.hmac.opad ) )
{
status = PSA_ERROR_NOT_SUPPORTED;
goto exit;
}
if( slot->type != PSA_KEY_TYPE_HMAC ) if( slot->type != PSA_KEY_TYPE_HMAC )
{ {
status = PSA_ERROR_INVALID_ARGUMENT; status = PSA_ERROR_INVALID_ARGUMENT;
goto exit; goto exit;
} }
status = psa_hmac_setup_internal( &operation->ctx.hmac, status = psa_hmac_setup_internal( &operation->ctx.hmac,
slot->data.raw.data, slot->data.raw.data,
slot->data.raw.bytes, slot->data.raw.bytes,
hash_alg ); hash_alg );
operation->mac_size = PSA_HASH_SIZE( hash_alg );
} }
else else
#endif /* MBEDTLS_MD_C */ #endif /* MBEDTLS_MD_C */
@ -1611,9 +1632,6 @@ static psa_status_t psa_hmac_finish_internal( psa_hmac_internal_data *hmac,
size_t block_size = psa_get_hash_block_size( hash_alg ); size_t block_size = psa_get_hash_block_size( hash_alg );
psa_status_t status; psa_status_t status;
if( block_size == 0 )
return( PSA_ERROR_NOT_SUPPORTED );
status = psa_hash_finish( &hmac->hash_ctx, tmp, sizeof( tmp ), &hash_size ); status = psa_hash_finish( &hmac->hash_ctx, tmp, sizeof( tmp ), &hash_size );
if( status != PSA_SUCCESS ) if( status != PSA_SUCCESS )
return( status ); return( status );