On Wed, Apr 17, 2024 at 08:48:23PM +0200, Ricardo Ribalda wrote:
> 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;
> }
>
You're right... There is a comment explaining why we multiply the
number of lines written by two, but it doesn't really clarify anything
for me:
/* Multiply linesdone by two, to take account of the other field */
What's the "other field"?
I kind of suspect that the stk1160_buffer_done() might be wrong as well.
vb2_set_plane_payload(&buf->vb.vb2_buf, 0, buf->bytesused);
^^^^^^^^^^^^^^
We're calculating the space left based on ->pos which can be reset to
zero in stk1160_process_isoc(). But ->bytesused isn't reset, so
potentially we could end up in a situation where ->bytesused is greater
than the ->length of the buffer. Should stk1160_process_isoc() set
->bytesused to zero as well?
regards,
dan carpenter
