linux-kernel - Re: [PATCH] media: pvrusb2: fix use after free on context disconnection

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Date:   Sun, 15 Oct 2023 20:49:57 -0500 (CDT)
From:   Mike Isely <isely@...ly.net>
To:     "Ricardo B. Marliere" <ricardo@...liere.net>
cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzbot+621409285c4156a009b3@...kaller.appspotmail.com,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] media: pvrusb2: fix use after free on context
 disconnection


Acked-by: Mike Isely <isely@...ox.com>

  -Mike

On Thu, 12 Oct 2023, Ricardo B. Marliere wrote:

> Upon module load, a kthread is created targeting the
> pvr2_context_thread_func function, which may call pvr2_context_destroy
> and thus call kfree() on the context object. However, that might happen
> before the usb hub_event handler is able to notify the driver. This
> patch adds a sanity check before the invalid read reported by syzbot,
> within the context disconnection call stack.
> 
> Fixes: e5be15c63804 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
> Reported-and-tested-by: syzbot+621409285c4156a009b3@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/000000000000a02a4205fff8eb92@google.com/
> Signed-off-by: Ricardo B. Marliere <ricardo@...liere.net>
> ---
>  drivers/media/usb/pvrusb2/pvrusb2-context.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/pvrusb2/pvrusb2-context.c b/drivers/media/usb/pvrusb2/pvrusb2-context.c
> index 14170a5d72b3..1764674de98b 100644
> --- a/drivers/media/usb/pvrusb2/pvrusb2-context.c
> +++ b/drivers/media/usb/pvrusb2/pvrusb2-context.c
> @@ -268,7 +268,8 @@ void pvr2_context_disconnect(struct pvr2_context *mp)
>  {
>  	pvr2_hdw_disconnect(mp->hdw);
>  	mp->disconnect_flag = !0;
> -	pvr2_context_notify(mp);
> +	if (!pvr2_context_shutok())
> +		pvr2_context_notify(mp);
>  }
>  
>  
>