Hi Dan
On Wed, 17 Apr 2024 at 19:51, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> The subtract in this condition is reversed. The ->length is the length
> of the buffer. The ->bytesused is how many bytes we have copied thus
> far. When the condition is reversed that means the result of the
> subtraction is always negative but since it's unsigned then the result
> is a very high positive value. That means the overflow check is never
> true.
>
> Fixes: 9cb2173e6ea8 ("[media] media: Add stk1160 new driver (easycap replacement)")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> This patch is untested, I just spotted it in review.
>
> When this bug is fixed, the two checks for negative values of "lencopy"
> could be removed. I wrote a version of this patch which removed the
> checks, but in the end I decided to leave the checks. They're harmless.
>
> drivers/media/usb/stk1160/stk1160-video.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/usb/stk1160/stk1160-video.c b/drivers/media/usb/stk1160/stk1160-video.c
> index 366f0e4a5dc0..bfb97ea352e7 100644
> --- a/drivers/media/usb/stk1160/stk1160-video.c
> +++ b/drivers/media/usb/stk1160/stk1160-video.c
> @@ -139,8 +139,8 @@ void stk1160_copy_video(struct stk1160 *dev, u8 *src, int len)
> * Check if we have enough space left in the buffer.
> * In that case, we force loop exit after copy.
> */
> - if (lencopy > buf->bytesused - buf->length) {
> - lencopy = buf->bytesused - buf->length;
> + if (lencopy > buf->length - buf->bytesused) {
> + lencopy = buf->length - buf->bytesused;
> remain = lencopy;
> }
I think it is a bit more complicated than bytesused.
bytesused does not take into consideration the actual position where
it is going to write.
What we really want to check is if
offset = dst - buf->mem;
if (offset + lencopy > buf->length) {
lencopy = buf->length - offset;
remain = lencopy;
}
>
> @@ -182,8 +182,8 @@ void stk1160_copy_video(struct stk1160 *dev, u8 *src, int len)
> * Check if we have enough space left in the buffer.
> * In that case, we force loop exit after copy.
> */
> - if (lencopy > buf->bytesused - buf->length) {
> - lencopy = buf->bytesused - buf->length;
> + if (lencopy > buf->length - buf->bytesused) {
> + lencopy = buf->length - buf->bytesused;
> remain = lencopy;
> }
>
> --
> 2.43.0
>
--
Ricardo Ribalda
