Re: [PATCH] mmc: vub300: fix Use-After-Free of inactivity_timer on disconnect and probe failure

[Johan Hovold <johan@kernel.org>]

On Wed, Aug 19, 2026 at 02:03:22AM +0500, Muhammad Bilal wrote:
> The vub300 driver arms inactivity_timer during probe and acquires a kref
> reference for the running timer. However, vub300_disconnect() sets
> vub300->interface = NULL and drops the driver's kref without shutting down
> the timer via timer_shutdown_sync().
> 
> If the timer expires after the host is removed and vub300 is freed,
> or if concurrent work items re-arm the timer,
> vub300_inactivity_timer_expired() accesses the already freed vub300
> structure, causing a Use-After-Free.

No, this cannot happen as the timer holds another reference.

> Fix this by explicitly shutting down inactivity_timer via
> timer_shutdown_sync() and releasing the timer's kref reference in
> vub300_disconnect() and probe error cleanup paths.
> 
> Fixes: 88095e7b473a ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")
> Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>

How was this "issue" found? Are you using an LLM?

> ---
>  drivers/mmc/host/vub300.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
> index 8e45dc1a4a12..9f84bd1531e2 100644
> --- a/drivers/mmc/host/vub300.c
> +++ b/drivers/mmc/host/vub300.c
> @@ -2350,6 +2350,8 @@ static int vub300_probe(struct usb_interface *interface,
>  
>  err_stop_io:
>  	vub300->interface = NULL;
> +	timer_shutdown_sync(&vub300->inactivity_timer);
> +	kref_put(&vub300->kref, vub300_delete);
>  	kref_put(&vub300->kref, vub300_delete);

And this results in a reference underflow.

Johan