On Wed, Apr 27, 2016 at 07:42:04AM +0200, Julia Lawall wrote:
>
>
> On Tue, 26 Apr 2016, Kees Cook wrote:
>
> > On Mon, Apr 25, 2016 at 7:50 AM, Pengfei Wang <wpengfein...@gmail.com>
> > wrote:
> > > Hello,
> > >
> > > I found this Double-Fetch bug in Linux-4.5/drivers/scsi/aacraid/commctrl.c
> > > when I was examining the source code.
> >
> > Thanks for these reports! I wrote a coccinelle script to find these,
> > but it requires some manual checking. For what it's worth, it found
> > your report as well:
> >
> > ./drivers/scsi/aacraid/commctrl.c:116:5-19: potentially dangerous
> > second copy_from_user()
> >
> > So I should probably get this added to the coccicheck run... Maybe it
> > can get some clean up from Julia. :)
>
> I looked a bit at the results, and didn't see anything obvious. What is
> the problem, exactly, and what would be a characteristic of a false
> positive?
>
copy_from_user(dest, src, sizeof(dest));
if (dest.extra > MAX_SIZE)
return -EINVAL;
copy_from_user(dest, src, sizeof(dest) + dest.extra);
for (i = 0; i < dest.extra; i++) {
dest.foo[i] = xxx;
We get dest.extra from the user, we verify the size, then we copy more
data from the user but that over writes dest.extra again. We use
dest.extra a second time without checking that it's still <= MAX_SIZE.
regards,
dan carpenter
