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

[Gustavo A. R. Silva]

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@xxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxxxx>

Thanks!
--
Gustavo