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

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Message-ID: <0ed29fbc-83b7-2ef0-1cb6-563908667f30@rkapl.cz>
Date:   Mon, 20 Nov 2017 22:41:55 +0100
From:   Roman Kapl <code@...pl.cz>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sched: crash on blocks with goto chain action

On 11/20/2017 06:54 PM, Cong Wang wrote:
> 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.

Was there a reason to hold all list entries in that trick? I thought 
that holding just the current element will be enough, but maybe not.