netdev - Re: [PATCH] net: sched: use temporary variable for actions indexes

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Message-ID: <CAM_iQpVb_BLCna0Thi+84sHS-Wp3T0AGh6Wb9j6k8DefSEDGfA@mail.gmail.com>
Date:   Thu, 1 Aug 2019 16:41:41 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     dmitrolin@...lanox.com
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Vlad Buslov <vladbu@...lanox.com>
Subject: Re: [PATCH] net: sched: use temporary variable for actions indexes

On Thu, Aug 1, 2019 at 6:03 AM <dmitrolin@...lanox.com> wrote:
>
> From: Dmytro Linkin <dmitrolin@...lanox.com>
>
> Currently init call of all actions (except ipt) init their 'parm'
> structure as a direct pointer to nla data in skb. This leads to race
> condition when some of the filter actions were initialized successfully
> (and were assigned with idr action index that was written directly
> into nla data), but then were deleted and retried (due to following
> action module missing or classifier-initiated retry), in which case
> action init code tries to insert action to idr with index that was
> assigned on previous iteration. During retry the index can be reused
> by another action that was inserted concurrently, which causes
> unintended action sharing between filters.
> To fix described race condition, save action idr index to temporary
> stack-allocated variable instead on nla data.
>
> Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
> Signed-off-by: Dmytro Linkin <dmitrolin@...lanox.com>
> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>


Acked-by: Cong Wang <xiyou.wangcong@...il.com>

This is a sad side-effect we have to deal with for this retry logic,
we have to restore all global status in each retry loop. :-(

Thanks.