Re: [PATCH] media: videobuf2: Fix integer overrun in allocation

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ricardo,

On Wed, Mar 10, 2021 at 08:58:39AM +0100, Ricardo Ribalda wrote:
> On Wed, Mar 10, 2021 at 8:49 AM Laurent Pinchart wrote:
> > On Wed, Mar 10, 2021 at 12:43:17AM +0100, Ricardo Ribalda wrote:
> > > The plane_length is an unsigned integer. So, if we have a size of
> > > 0xffffffff bytes we incorrectly allocate 0 bytes instead of 1 << 32.
> > >
> > > Cc: stable@vger.kernel.org
> > > Fixes: 7f8414594e47 ("[media] media: videobuf2: fix the length check for mmap")
> > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > ---
> > >  drivers/media/common/videobuf2/videobuf2-core.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > > index 02281d13505f..543da515c761 100644
> > > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > > @@ -223,8 +223,10 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
> > >        * NOTE: mmapped areas should be page aligned
> > >        */
> > >       for (plane = 0; plane < vb->num_planes; ++plane) {
> > > +             unsigned long size = vb->planes[plane].length;
> >
> > unsigned long is still 32-bit on 32-bit platforms.
> >
> > > +
> > >               /* Memops alloc requires size to be page aligned. */
> > > -             unsigned long size = PAGE_ALIGN(vb->planes[plane].length);
> > > +             size = PAGE_ALIGN(size);
> > >
> > >               /* Did it wrap around? */
> > >               if (size < vb->planes[plane].length)
> >
> > Doesn't this address the issue already ?
> 
> Yes and no. If you need to allocate 0xffffffff you are still affected
> by the underrun. The core will return an error instead of doing the
> allocation.
> 
> (yes, I know it is a lot of memory for a buffer)

That's my point, I don't think there's a need for this :-) Especially
with v4l2_buffer.m.offset being a __u32, we are limited to 4GB for *all*
buffers.

-- 
Regards,

Laurent Pinchart