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

[Sean Young <sean@mess.org>]

On Fri, Sep 18, 2026 at 11:18:51AM +0530, Deepanshu Kartikey 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.
> 
> Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
> Reported-by: syzbot+9bfac891bdd42eb708fc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=9bfac891bdd42eb708fc
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
>  drivers/media/rc/imon.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
> index 049a73b5f882..9341dbe03b57 100644
> --- a/drivers/media/rc/imon.c
> +++ b/drivers/media/rc/imon.c
> @@ -502,6 +502,7 @@ static void free_imon_context(struct imon_context *ictx)
>  	kfree_rcu(ictx, rcu);
>  
>  	dev_dbg(dev, "%s: iMON context freed\n", __func__);

The dev is only referenced in dev_dbg() here.

The debug statement is pretty pointless anyway so why don't we remove
that instead.


Sean

> +	put_device(dev);
>  }
>  
>  /*
> @@ -2253,7 +2254,7 @@ 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 +2315,7 @@ 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
>