Re: [PATCH 1/3] videobuf2-core: Prevent size alignment wrapping buffer size to 0

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

Hi Sakari,

Thank you for the patch.

On Thursday, 13 December 2018 12:40:04 EET Sakari Ailus wrote:
> PAGE_ALIGN() may wrap the buffer size around to 0. Prevent this by
> checking that the aligned value is not smaller than the unaligned one.
> 
> 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-core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c
> b/drivers/media/common/videobuf2/videobuf2-core.c index
> 0ca81d495bdaf..0234ddbfa4de2 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -207,6 +207,10 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
>  	for (plane = 0; plane < vb->num_planes; ++plane) {
>  		unsigned long size = PAGE_ALIGN(vb->planes[plane].length);
> 
> +		/* Did it wrap around? */
> +		if (size < vb->planes[plane].length)
> +			goto free;
> +
>  		mem_priv = call_ptr_memop(vb, alloc,
>  				q->alloc_devs[plane] ? : q->dev,
>  				q->dma_attrs, size, q->dma_dir, q->gfp_flags);

Wouldn't it be better to reject length > INT_MAX (or some variations of that) 
a few steps before, for instance just before calling __vb2_queue_alloc() ? 
There's already a check in vb2_core_reqbufs():

        /* Check that driver has set sane values */
        if (WARN_ON(!num_planes))
                return -EINVAL;

        for (i = 0; i < num_planes; i++)
                if (WARN_ON(!plane_sizes[i]))
                        return -EINVAL;

It could be extended to validate the sizes against wrap-around, and moved to a 
separate function to be called in vb2_core_create_bufs() as well (as those 
checks are missing there). Alternatively, the checks could be moved to the 
beginning of __vb2_queue_alloc().

-- 
Regards,

Laurent Pinchart