Re: [PATCH v3 1/1] usbnet:fix NPE during rx_complete

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Apr 02, 2025 at 04:06:29PM +0800, Ying Lu wrote:
> From: Ying Lu <luying1@xiaomi.com>
> 
> Missing usbnet_going_away Check in Critical Path.
> The usb_submit_urb function lacks a usbnet_going_away
> validation, whereas __usbnet_queue_skb includes this check.
> 
> This inconsistency creates a race condition where:
> A URB request may succeed, but the corresponding SKB data
> fails to be queued.
> 
> Subsequent processes:
> (e.g., rx_complete → defer_bh → __skb_unlink(skb, list))
> attempt to access skb->next, triggering a NULL pointer
> dereference (Kernel Panic).
> 
> Fixes: 04e906839a05 ("usbnet: fix cyclical race on disconnect with work queue")
> Signed-off-by: Ying Lu <luying1@xiaomi.com>
> ---
>  drivers/net/usb/usbnet.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 44179f4e807f..5161bb5d824b 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -519,7 +519,8 @@ static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
>  	    netif_device_present (dev->net) &&
>  	    test_bit(EVENT_DEV_OPEN, &dev->flags) &&
>  	    !test_bit (EVENT_RX_HALT, &dev->flags) &&
> -	    !test_bit (EVENT_DEV_ASLEEP, &dev->flags)) {
> +	    !test_bit (EVENT_DEV_ASLEEP, &dev->flags) &&
> +	    !usbnet_going_away(dev)) {
>  		switch (retval = usb_submit_urb (urb, GFP_ATOMIC)) {
>  		case -EPIPE:
>  			usbnet_defer_kevent (dev, EVENT_RX_HALT);
> @@ -540,8 +541,7 @@ static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
>  			tasklet_schedule (&dev->bh);
>  			break;
>  		case 0:
> -			if (!usbnet_going_away(dev))
> -				__usbnet_queue_skb(&dev->rxq, skb, rx_start);
> +			__usbnet_queue_skb(&dev->rxq, skb, rx_start);
>  		}
>  	} else {
>  		netif_dbg(dev, ifdown, dev->net, "rx: stopped\n");
> -- 
> 2.49.0
> 
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
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  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
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thanks,

greg k-h's patch email bot