netdev - Re: [PATCH v2] net: fix a double free issue for neighbour entry

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Message-ID: <1432118737.4060.21.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 20 May 2015 03:45:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ying Xue <ying.xue@...driver.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	alexei@...estorage.com, joern@...estorage.com, ja@....bg
Subject: Re: [PATCH v2] net: fix a double free issue for neighbour entry

On Wed, 2015-05-20 at 15:01 +0800, Ying Xue wrote:

> Time 4:
> CPU 0:
> Release the neigh whose refcnt was increased from 0 to zero.
> neigh_release() is called by someone. As the neigh is already freed, panic
> happens!!!

There is a bug for sure, although I never saw it ever happening.

I am only saying your 'fix' is not appropriate.

You focus on refcnt which is the wrong thing to test in this context.

Even if we decided to remove RCU locking and go back to rwlock, refcnt
would not be the thing to test.


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