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

[Cong Wang <xiyou.wangcong@gmail.com>]

On Thu, Aug 1, 2019 at 6:03 AM <dmitrolin@mellanox.com> wrote:
>
> From: Dmytro Linkin <dmitrolin@mellanox.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@mellanox.com>
> Signed-off-by: Vlad Buslov <vladbu@mellanox.com>


Acked-by: Cong Wang <xiyou.wangcong@gmail.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.