netdev - Re: [PATCH net-next] net: sched: fix potential use-after-free in __tcf_chain

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Message-Id: <20190308.151817.179991915660799550.davem@davemloft.net>
Date:   Fri, 08 Mar 2019 15:18:17 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     vladbu@...lanox.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us
Subject: Re: [PATCH net-next] net: sched: fix potential use-after-free in
 __tcf_chain_put()

From: Vlad Buslov <vladbu@...lanox.com>
Date: Wed,  6 Mar 2019 17:50:43 +0200

> When used with unlocked classifier that have filters attached to actions
> with goto chain, __tcf_chain_put() for last non action reference can race
> with calls to same function from action cleanup code that releases last
> action reference. In this case action cleanup handler could free the chain
> if it executes after all references to chain were released, but before all
> concurrent users finished using it. Modify __tcf_chain_put() to only access
> tcf_chain fields when holding block->lock. Remove local variables that were
> used to cache some tcf_chain fields and are no longer needed because their
> values can now be obtained directly from chain under block->lock
> protection.
> 
> Fixes: 726d061286ce ("net: sched: prevent insertion of new classifiers during chain flush")
> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

Applied, thanks Vlad.