Re: [PATCH] media: dvbdev: fix uaf in dvb_remove_device()

[Ricardo Ribalda]

On Thu, 27 Aug 2026 at 05:52, Jeffin Philip <jeffinphilip14@xxxxxxxxx> wrote:
>
> On Sat, 22 Aug 2026 16:52:56 +0530, Jeffin Philip wrote:
> >In dvb_remove_device(), dvb_media_device_free(), device_destroy()
> >and list_del() all dereference dvbdev regardless of its refcount.
> >Thus, if refcount for dvbdev is 1, it can be freed and we
> >operate on freed memory causing a UAF. Fix this by moving
> >dvb_device_put() at the end of dvb_remove_device() so dvbdev
> >members can be safely freed and assigned NULL when dvbdev is alive.
> >

Reviewed-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>

> >Reported-by: syzbot+37578f730d38898f4b74@xxxxxxxxxxxxxxxxxxxxxxxxx
> >Closes: https://syzkaller.appspot.com/bug?extid=37578f730d38898f4b74
> >Fixes: 0fc044b2b5e2 ("media: dvbdev: adopts refcnt to avoid UAF")
> >Cc: stable@xxxxxxxxxxxxxxx
> >Signed-off-by: Jeffin Philip <jeffinphilip14@xxxxxxxxx>
> >---
> > drivers/media/dvb-core/dvbdev.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
> >index d753d329502a..9aa4b8fd7379 100644
> >--- a/drivers/media/dvb-core/dvbdev.c
> >+++ b/drivers/media/dvb-core/dvbdev.c
> >@@ -598,7 +598,6 @@ void dvb_remove_device(struct dvb_device *dvbdev)
> >
> >       down_write(&minor_rwsem);
> >       dvb_minors[dvbdev->minor] = NULL;
> >-      dvb_device_put(dvbdev);
> >       up_write(&minor_rwsem);
> >
> >       dvb_media_device_free(dvbdev);
> >@@ -606,6 +605,8 @@ void dvb_remove_device(struct dvb_device *dvbdev)
> >       device_destroy(dvb_class, MKDEV(DVB_MAJOR, dvbdev->minor));
> >
> >       list_del(&dvbdev->list_head);
> >+
> >+      dvb_device_put(dvbdev);
> > }
> > EXPORT_SYMBOL(dvb_remove_device);
> >
> >--
>
> Friendly ping, let me know if you want me to fix anything.
>
> Thanks,
> Jeffin.



-- 
Ricardo Ribalda