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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
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@ -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 );