Re: [PATCH v2] media: imon: fix use-after-free in display_close via dev_dbg

[Deepanshu Kartikey]

On Mon, Sep 28, 2026 at 5:42 PM Deepanshu Kartikey
<kartikey406@xxxxxxxxx> wrote:
>
> ictx->dev is a raw pointer to the usb_interface's embedded device,
> cached in imon_init_intf0() without taking a reference. On
> disconnect, usb_disconnect() can drop the last reference on the
> interface and free it while a userspace fd for /dev/lcd0 is still
> open. When that fd is later closed, display_close() dereferences
> the now-freed ictx->dev via dev_dbg(), causing a use-after-free.
>
> Fix by pinning the device with get_device() when ictx->dev is
> assigned, and releasing it with put_device() when ictx is freed.
>
> Also drop the dev_dbg() in free_imon_context(), which only printed
> a debug message and is no longer needed.
>
> Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
> Reported-by: syzbot+9bfac891bdd42eb708fc@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=9bfac891bdd42eb708fc
> Link: http://lore.kernel.org/all/20260918054851.26083-1-kartikey406@xxxxxxxxx/T/ [v1]
> Signed-off-by: Deepanshu Kartikey <kartikey406@xxxxxxxxx>
> ---
> v2:
> - Remove the dev_dbg() in free_imon_context(), as suggested by
>   Sean Young.
> ---
>  drivers/media/rc/imon.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
> index 049a73b5f882..562a70186db4 100644
> --- a/drivers/media/rc/imon.c
> +++ b/drivers/media/rc/imon.c
> @@ -501,7 +501,7 @@ static void free_imon_context(struct imon_context *ictx)
>         usb_free_urb(ictx->rx_urb_intf1);
>         kfree_rcu(ictx, rcu);
>
> -       dev_dbg(dev, "%s: iMON context freed\n", __func__);
> +       put_device(dev);
>  }
>
>  /*
> @@ -2253,7 +2253,7 @@ static struct imon_context *imon_init_intf0(struct usb_interface *intf,
>
>         mutex_lock(&ictx->lock);
>
> -       ictx->dev = dev;
> +       ictx->dev = get_device(dev);
>         ictx->usbdev_intf0 = interface_to_usbdev(intf);
>         ictx->rx_urb_intf0 = rx_urb;
>         ictx->tx_urb = tx_urb;
> @@ -2314,6 +2314,7 @@ static struct imon_context *imon_init_intf0(struct usb_interface *intf,
>  find_endpoint_failed:
>         mutex_unlock(&ictx->lock);
>         usb_free_urb(tx_urb);
> +       put_device(ictx->dev);
>  tx_urb_alloc_failed:
>         usb_free_urb(rx_urb);
>  rx_urb_alloc_failed:
> --
> 2.34.1
>

Please disregard this patch.

Thanks

Deepanshu