On 4/10/19 4:28 PM, Sumit Gupta wrote:
> From: sumitg <sumitg@xxxxxxxxxx>
>
> Fixing use-after-free within __v4l2_ctrl_handler_setup().
> Memory is being freed with kfree(new_ref) for duplicate
> control reference entry but cluster is still referring
> to the duplicate entry. Change done to point cluster to
> original reference instead of duplicate which is freed.
>
> ==================================================================
> BUG: KASAN: use-after-free in __v4l2_ctrl_handler_setup+0x388/0x428
> Read of size 8 at addr ffffffc324e78618 by task systemd-udevd/312
>
> Allocated by task 312:
>
> Freed by task 312:
>
> The buggy address belongs to the object at ffffffc324e78600
> which belongs to the cache kmalloc-64 of size 64
> The buggy address is located 24 bytes inside of
> 64-byte region [ffffffc324e78600, ffffffc324e78640)
> The buggy address belongs to the page:
> page:ffffffbf0c939e00 count:1 mapcount:0 mapping:
> (null) index:0xffffffc324e78f80
> flags: 0x4000000000000100(slab)
> raw: 4000000000000100 0000000000000000 ffffffc324e78f80 000000018020001a
> raw: 0000000000000000 0000000100000001 ffffffc37040fb80 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffffffc324e78500: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffffffc324e78580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >ffffffc324e78600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ^
> ffffffc324e78680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffffffc324e78700: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
> Signed-off-by: sumitg <sumitg@xxxxxxxxxx>
> ---
> drivers/media/v4l2-core/v4l2-ctrls.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index 5e3806f..e971bab 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -2182,6 +2182,7 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
> continue;
> /* Don't add duplicates */
> if (ref->ctrl->id == id) {
> + ctrl->cluster = &ref->ctrl;
> kfree(new_ref);
> goto unlock;
> }
>
I don't like this solution. Instead move this code:
if (ctrl->handler == hdl) {
/* By default each control starts in a cluster of its own.
new_ref->ctrl is basically a cluster array with one
element, so that's perfect to use as the cluster pointer.
But only do this for the handler that owns the control. */
ctrl->cluster = &new_ref->ctrl;
ctrl->ncontrols = 1;
}
to after the insert_in_hash label.
That way the ctrl->cluster pointer is only updated if everything is OK.
Nice catch, BTW!
Regards,
Hans
