netdev - Re: [PATCH net] rhashtable: prevent work queue schedule while dismantling

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Date:   Mon, 1 Oct 2018 09:25:35 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH net] rhashtable: prevent work queue schedule while dismantling

On Mon, Oct 1, 2018 at 6:40 AM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Mon, Oct 01, 2018 at 06:16:27AM -0700, Eric Dumazet wrote:
> > syszbot found an interesting use-after-free [1] happening
> > while IPv4 fragment rhashtable was destroyed at netns dismantle.
> >
> > While no insertions can possibly happen at the time a dismantling
> > netns is destroying this rhashtable, timers can still fire and
> > attempt to remove elements from this rhashtable.
>
> Hmm, I think that's your real problem.  rhashtable_free_and_destroy
> doesn't take any locks with respect to the normal insertion/removal
> path so it definitely isn't safe to call it while you're still
> invoking the normal rhashtable remove function.
>

Ah... for some reason I thought it was ok to delete elems while
rhashtable_free_and_destroy() was running.

I would love not having to use a rhashtable_walk...() to first expunge
the hash table
before rhashtable_destroy()