netdev - Re: [PATCH] net: sched: crash on blocks with goto chain action

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Message-ID: <CAM_iQpW7iQ7R-e03UywDjBh5xQJcE3N=fxHeCmeF_AdM4RR-zQ@mail.gmail.com>
Date:   Mon, 20 Nov 2017 09:54:46 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Roman Kapl <code@...pl.cz>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sched: crash on blocks with goto chain action

On Sun, Nov 19, 2017 at 8:17 AM, Roman Kapl <code@...pl.cz> wrote:
> tcf_block_put_ext has assumed that all filters (and thus their goto
> actions) are destroyed in RCU callback and thus can not race with our
> list iteration. However, that is not true during netns cleanup (see
> tcf_exts_get_net comment).
>
> Prevent the user after free by holding the current list element we are
> iterating over (foreach_safe is not enough).

Hmm...

Looks like we need to restore the trick we used previously, that is
holding refcnt for all list entries before this list iteration.