Re: [PATCH][next] ASoC: sigmadsp: Add __counted_by for struct sigmadsp_data and use struct_size()

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 10/10/23 00:03, Kees Cook wrote:
> On Mon, Oct 09, 2023 at 03:24:23PM -0600, Gustavo A. R. Silva wrote:
>> Prepare for the coming implementation by GCC and Clang of the __counted_by
>> attribute. Flexible array members annotated with __counted_by can have
>> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
>> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
>> functions).
>>
>> While there, use struct_size() and size_sub() helpers, instead of the
>> open-coded version, to calculate the size for the allocation of the
>> whole flexible structure, including of course, the flexible-array
>> member.
>>
>> This code was found with the help of Coccinelle, and audited and
>> fixed manually.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>> ---
>>   sound/soc/codecs/sigmadsp.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/sound/soc/codecs/sigmadsp.c b/sound/soc/codecs/sigmadsp.c
>> index b93c078a8040..56546e2394ab 100644
>> --- a/sound/soc/codecs/sigmadsp.c
>> +++ b/sound/soc/codecs/sigmadsp.c
>> @@ -43,7 +43,7 @@ struct sigmadsp_data {
>>   	uint32_t samplerates;
>>   	unsigned int addr;
>>   	unsigned int length;
>> -	uint8_t data[];
>> +	uint8_t data[] __counted_by(length);
>>   };
>>   
>>   struct sigma_fw_chunk {
>> @@ -270,7 +270,7 @@ static int sigma_fw_load_data(struct sigmadsp *sigmadsp,
>>   
>>   	length -= sizeof(*data_chunk);
>>   
>> -	data = kzalloc(sizeof(*data) + length, GFP_KERNEL);
>> +	data = kzalloc(struct_size(data, data, length), GFP_KERNEL);
>>   	if (!data)
>>   		return -ENOMEM;
>>   
>> @@ -413,7 +413,8 @@ static int process_sigma_action(struct sigmadsp *sigmadsp,
>>   		if (len < 3)
>>   			return -EINVAL;
>>   
>> -		data = kzalloc(sizeof(*data) + len - 2, GFP_KERNEL);
>> +		data = kzalloc(struct_size(data, data, size_sub(len, 2)),
>> +			       GFP_KERNEL);
> 
> Since len was just size-checked before the alloc, size_sub() is a bit of
> overkill, but it's not technically wrong. :P

Oops.. yep, you're right, I totally overlooked that check.

> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 

Thanks!
--
Gustavo