Re: [PATCH 2/3] videobuf2-dma-sg: Prevent size from overflowing

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

On Thursday, 13 December 2018 15:00:23 EET Sakari Ailus wrote:
> Hi Laurent,
> 
> On Thu, Dec 13, 2018 at 02:57:46PM +0200, Laurent Pinchart wrote:
> > Hi Sakari,
> > 
> > Thank you for the patch.
> > 
> > On Thursday, 13 December 2018 12:40:05 EET Sakari Ailus wrote:
> > > buf->size is an unsigned long; casting that to int will lead to an
> > > overflow if buf->size exceeds INT_MAX.
> > > 
> > > Fix this by changing the type to unsigned long instead. This is possible
> > > as the buf->size is always aligned to PAGE_SIZE, and therefore the size
> > > will never have values lesser than 0.
> > 
> > This feels a bit fragile to me. We at least need a big comment in the code
> > to explain this. Another option would be a size -= min(..., size) just to
> > make sure.
> 
> I was thinking of something like:
> 
> 	if (WARN_ON(size & ~PAGE_MASK))
> 		return -ENOMEM;
> 
> But I opted to writing the third patch as this is not the only place where
> the page alignment could be relevant.
> 
> What do you think?

I'd do both :-)

> > > Note on backporting to stable: the file used to be under
> > > drivers/media/v4l2-core, it was moved to the current location after
> > > 4.14.
> > > 
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > Cc: stable@vger.kernel.org
> > > ---
> > > 
> > >  drivers/media/common/videobuf2/videobuf2-dma-sg.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> > > b/drivers/media/common/videobuf2/videobuf2-dma-sg.c index
> > > 015e737095cdd..e9bfea986cc47 100644
> > > --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> > > +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> > > @@ -59,7 +59,7 @@ static int vb2_dma_sg_alloc_compacted(struct
> > > vb2_dma_sg_buf *buf, gfp_t gfp_flags)
> > > 
> > >  {
> > >  
> > >  	unsigned int last_page = 0;
> > > 
> > > -	int size = buf->size;
> > > +	unsigned long size = buf->size;
> > > 
> > >  	while (size > 0) {
> > >  	
> > >  		struct page *pages;


-- 
Regards,

Laurent Pinchart