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