Messages in this thread Patch in this message | | | From | Ricardo Ribalda <> | Date | Wed, 17 Apr 2024 20:48:23 +0200 | Subject | Re: [PATCH] media: stk1160: fix some bounds checking in stk1160_copy_video() |
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Hi Dan
On Wed, 17 Apr 2024 at 19:51, Dan Carpenter <dan.carpenter@linaro.org> 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@linaro.org> > --- > 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
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