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Do not decrypt a container key bag that is already plaintext #91

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willmcginnis wants to merge 1 commit into from
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Do not decrypt a container key bag that is already plaintext #91

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249 changes: 182 additions & 67 deletions libfsapfs/libfsapfs_container_key_bag.c
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Original file line number Diff line number Diff line change
Expand Up @@ -177,6 +177,85 @@ int libfsapfs_container_key_bag_free(
return( result );
}

/* Determines if container key bag data is stored unencrypted
* A container key bag can be stored unencrypted on disk, in which case
* decrypting it destroys it. This check is READ-ONLY: it inspects
* the data in place and touches no container key bag state, so a negative result
* leaves nothing behind for the caller to roll back.
* Returns 1 if the data is an unencrypted container key bag, 0 if not or -1 on error
*/
int libfsapfs_container_key_bag_data_is_unencrypted(
const uint8_t *data,
size_t data_size,
libcerror_error_t **error )
{
static char *function = "libfsapfs_container_key_bag_data_is_unencrypted";
uint64_t calculated_checksum = 0;
uint64_t stored_checksum = 0;
uint32_t object_subtype = 0;
uint32_t object_type = 0;

if( data == NULL )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_ARGUMENTS,
LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,
"%s: invalid data.",
function );

return( -1 );
}
/* Note that libfsapfs_checksum_calculate_fletcher64 returns an error for a
* size that is not a multiple of 4, which is a "not an unencrypted container
* key bag" case rather than an error as far as this function is concerned.
*/
if( ( data_size < sizeof( fsapfs_object_t ) )
|| ( data_size > (size_t) SSIZE_MAX )
|| ( ( data_size % 4 ) != 0 ) )
{
return( 0 );
}
byte_stream_copy_to_uint32_little_endian(
( (fsapfs_object_t *) data )->type,
object_type );

byte_stream_copy_to_uint32_little_endian(
( (fsapfs_object_t *) data )->subtype,
object_subtype );

if( ( object_type != 0x6b657973UL )
|| ( object_subtype != 0x00000000UL ) )
{
return( 0 );
}
byte_stream_copy_to_uint64_little_endian(
( (fsapfs_object_t *) data )->checksum,
stored_checksum );

if( libfsapfs_checksum_calculate_fletcher64(
&calculated_checksum,
&( data[ 8 ] ),
data_size - 8,
0,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_SET_FAILED,
"%s: unable to calculate Fletcher-64 checksum.",
function );

return( -1 );
}
if( stored_checksum != calculated_checksum )
{
return( 0 );
}
return( 1 );
}

/* Reads the container key bag
* Returns 1 if successful, 0 if the object type does not match or -1 on error
*/
Expand All @@ -194,6 +273,7 @@ int libfsapfs_container_key_bag_read_file_io_handle(
uint8_t *encrypted_data = NULL;
static char *function = "libfsapfs_container_key_bag_read_file_io_handle";
ssize_t read_count = 0;
int is_unencrypted = 0;
int result = 0;

if( container_key_bag == NULL )
Expand Down Expand Up @@ -285,88 +365,123 @@ int libfsapfs_container_key_bag_read_file_io_handle(

goto on_error;
}
data = (uint8_t *) memory_allocate(
sizeof( uint8_t ) * (size_t) data_size );

if( data == NULL )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_MEMORY,
LIBCERROR_MEMORY_ERROR_INSUFFICIENT,
"%s: unable to create data.",
function );
is_unencrypted = libfsapfs_container_key_bag_data_is_unencrypted(

@joachimmetz joachimmetz Sep 17, 2026

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I'll bundle the necessary changes into another PR, was wondering about the approach here.

Instead of calling into libfsapfs_container_key_bag_data_is_unencrypted why not check for the unencrypted container key bag signature here, and have libfsapfs_container_key_bag_read_data validate the checksum?

encrypted_data,
(size_t) data_size,
error );

goto on_error;
}
if( libfsapfs_encryption_context_initialize(
&encryption_context,
LIBFSAPFS_ENCRYPTION_METHOD_AES_128_XTS,
error ) != 1 )
if( is_unencrypted == -1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_INITIALIZE_FAILED,
"%s: unable to initialize encryption context.",
LIBCERROR_RUNTIME_ERROR_GET_FAILED,
"%s: unable to determine if container key bag data is unencrypted.",
function );

goto on_error;
}
if( libfsapfs_encryption_context_set_keys(
encryption_context,
container_identifier,
16,
container_identifier,
16,
error ) != 1 )
if( is_unencrypted != 0 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_SET_FAILED,
"%s: unable to set keys in encryption context.",
function );

goto on_error;
#if defined( HAVE_DEBUG_OUTPUT )
if( libcnotify_verbose != 0 )
{
libcnotify_printf(
"%s: container key bag data is stored unencrypted - not decrypting.\n",
function );
}
#endif
/* Take ownership of the buffer as read, so the single
* libfsapfs_container_key_bag_read_data call below is unchanged.
*/
data = encrypted_data;
encrypted_data = NULL;
}
if( libfsapfs_encryption_context_crypt(
encryption_context,
LIBCAES_CRYPT_MODE_DECRYPT,
encrypted_data,
(size_t) data_size,
data,
(size_t) data_size,
(uint64_t) ( file_offset / io_handle->bytes_per_sector ),
io_handle->bytes_per_sector,
error ) != 1 )
else
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_ENCRYPTION,
LIBCERROR_ENCRYPTION_ERROR_DECRYPT_FAILED,
"%s: unable to decrypt data.",
function );
data = (uint8_t *) memory_allocate(
sizeof( uint8_t ) * (size_t) data_size );

goto on_error;
}
if( libfsapfs_encryption_context_free(
&encryption_context,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_FINALIZE_FAILED,
"%s: unable to free encryption context.",
function );
if( data == NULL )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_MEMORY,
LIBCERROR_MEMORY_ERROR_INSUFFICIENT,
"%s: unable to create data.",
function );

goto on_error;
}
memory_free(
encrypted_data );
goto on_error;
}
if( libfsapfs_encryption_context_initialize(
&encryption_context,
LIBFSAPFS_ENCRYPTION_METHOD_AES_128_XTS,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_INITIALIZE_FAILED,
"%s: unable to initialize encryption context.",
function );

encrypted_data = NULL;
goto on_error;
}
if( libfsapfs_encryption_context_set_keys(
encryption_context,
container_identifier,
16,
container_identifier,
16,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_SET_FAILED,
"%s: unable to set keys in encryption context.",
function );

goto on_error;
}
if( libfsapfs_encryption_context_crypt(
encryption_context,
LIBCAES_CRYPT_MODE_DECRYPT,
encrypted_data,
(size_t) data_size,
data,
(size_t) data_size,
(uint64_t) ( file_offset / io_handle->bytes_per_sector ),
io_handle->bytes_per_sector,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_ENCRYPTION,
LIBCERROR_ENCRYPTION_ERROR_DECRYPT_FAILED,
"%s: unable to decrypt data.",
function );

goto on_error;
}
if( libfsapfs_encryption_context_free(
&encryption_context,
error ) != 1 )
{
libcerror_error_set(
error,
LIBCERROR_ERROR_DOMAIN_RUNTIME,
LIBCERROR_RUNTIME_ERROR_FINALIZE_FAILED,
"%s: unable to free encryption context.",
function );

goto on_error;
}
memory_free(
encrypted_data );

encrypted_data = NULL;
}

#if defined( HAVE_DEBUG_OUTPUT )
if( libcnotify_verbose != 0 )
Expand Down
5 changes: 5 additions & 0 deletions libfsapfs/libfsapfs_container_key_bag.h
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,11 @@ int libfsapfs_container_key_bag_free(
libfsapfs_container_key_bag_t **container_key_bag,
libcerror_error_t **error );

int libfsapfs_container_key_bag_data_is_unencrypted(
const uint8_t *data,
size_t data_size,
libcerror_error_t **error );

int libfsapfs_container_key_bag_read_file_io_handle(
libfsapfs_container_key_bag_t *container_key_bag,
libfsapfs_io_handle_t *io_handle,
Expand Down
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