linux-kernel - Re: [PATCH] net: usb: fix possible use-after-free in smsc75xx

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Date:   Tue, 15 Jun 2021 09:38:28 +0200
From:   Greg KH <greg@...ah.com>
To:     Dongliang Mu <mudongliangabcd@...il.com>
Cc:     steve.glendinning@...well.net, davem@...emloft.net,
        kuba@...nel.org, paskripkin@...il.com, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: usb: fix possible use-after-free in smsc75xx_bind

On Mon, Jun 14, 2021 at 11:37:12PM +0800, Dongliang Mu wrote:
> The commit 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
> fails to clean up the work scheduled in smsc75xx_reset->
> smsc75xx_set_multicast, which leads to use-after-free if the work is
> scheduled to start after the deallocation. In addition, this patch also
> removes one dangling pointer - dev->data[0].
> 
> This patch calls cancel_work_sync to cancel the schedule work and set
> the dangling pointer to NULL.
> 
> Fixes: 46a8b29c6306 ("net: usb: fix memory leak in smsc75xx_bind")
> Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> ---
>  drivers/net/usb/smsc75xx.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
> index b286993da67c..f81740fcc8d5 100644
> --- a/drivers/net/usb/smsc75xx.c
> +++ b/drivers/net/usb/smsc75xx.c
> @@ -1504,7 +1504,10 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
>  	return 0;
>  
>  err:
> +	cancel_work_sync(&pdata->set_multicast);
>  	kfree(pdata);
> +	pdata = NULL;

Why do you have to set pdata to NULL afterward?

thanks,

greg k-h