netdev - Re: [PATCH 3/3] usbnet: fix skb traversing races during unlink(v1)

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Date:	Tue, 15 May 2012 13:42:30 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	tom.leiming@...il.com
Cc:	gregkh@...uxfoundation.org, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, huajun.li.lee@...il.com,
	oneukum@...e.de, stable@...nel.org
Subject: Re: [PATCH 3/3] usbnet: fix skb traversing races during unlink(v1)

From: Ming Lei <tom.leiming@...il.com>
Date: Thu, 3 May 2012 09:04:50 +0800

>>>From a87ff961f0a5d50223bd084dfac4fe5ce84f3913 Mon Sep 17 00:00:00 2001
> From: Ming Lei <tom.leiming@...il.com>
> Date: Thu, 26 Apr 2012 11:33:46 +0800
> Subject: [PATCH] usbnet: fix skb traversing races during unlink(v2)
> 
> Commit 4231d47e6fe69f061f96c98c30eaf9fb4c14b96d(net/usbnet: avoid
> recursive locking in usbnet_stop()) fixes the recursive locking
> problem by releasing the skb queue lock before unlink, but may
> cause skb traversing races:
> 	- after URB is unlinked and the queue lock is released,
> 	the refered skb and skb->next may be moved to done queue,
> 	even be released
> 	- in skb_queue_walk_safe, the next skb is still obtained
> 	by next pointer of the last skb
> 	- so maybe trigger oops or other problems
> 
> This patch extends the usage of entry->state to describe 'start_unlink'
> state, so always holding the queue(rx/tx) lock to change the state if
> the referd skb is in rx or tx queue because we need to know if the
> refered urb has been started unlinking in unlink_urbs.
> 
> The other part of this patch is based on Huajun's patch:
> always traverse from head of the tx/rx queue to get skb which is
> to be unlinked but not been started unlinking.
> 
> Signed-off-by: Huajun Li <huajun.li.lee@...il.com>
> Signed-off-by: Ming Lei <tom.leiming@...il.com>

Applied.
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