linux-kernel - Re: KASAN: use-after-free Read in tcp_write_timer

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Date:   Wed, 5 Apr 2023 21:47:54 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     bpf@...r.kernel.org, davem@...emloft.net, dsahern@...nel.org,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com, threeearcat@...il.com,
        yoshfuji@...ux-ipv6.org
Subject: Re: KASAN: use-after-free Read in tcp_write_timer_handler

On Wed, Apr 5, 2023 at 9:42 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> From:   Eric Dumazet <edumazet@...gle.com>
> Date:   Wed, 5 Apr 2023 13:28:16 +0200
> > On Wed, Apr 5, 2023 at 12:41 PM Dae R. Jeong <threeearcat@...il.com> wrote:
> > >
> > > Hi,
> > >
> > > We observed an issue "KASAN: use-after-free Read in tcp_write_timer_handler" during fuzzing.
> > >
> > > Unfortunately, we have not found a reproducer for the crash yet. We
> > > will inform you if we have any update on this crash.  Detailed crash
> > > information is attached below.
> > >
> >
> > Thanks for the report.
> >
> > I have dozens of similar syzbot reports, with no repro.
> >
> > I usually hold them, because otherwise it is just noise to mailing lists.
> >
> > Normally, all user TCP sockets hold a reference on the netns
> >
> > In all these cases, we see a netns being dismantled while there is at
> > least one socket with a live timer.
> >
> > This is therefore a kernel TCP socket, for which we do not have yet
> > debugging infra ( REF_TRACKER )
> >
> > CONFIG_NET_DEV_REFCNT_TRACKER=y is helping to detect too many dev_put(),
> > we need something tracking the "kernel sockets" as well.
>
> Maybe I missed something, but we track kernel sockets with netns
> by notrefcnt_tracker ?

Oh right, I forgot I did this already :)

commit 0cafd77dcd032d1687efaba5598cf07bce85997f
Author: Eric Dumazet <edumazet@...gle.com>
Date:   Thu Oct 20 23:20:18 2022 +0000

    net: add a refcount tracker for kernel sockets

Dae, make sure to not send reports based on old kernels.

Using 6.0-rc7 is a waste of your time, and everyone else reading this thread.

I confess I did not check this, and I really should do that all the time.



>
> I thought now CONFIG_NET_NS_REFCNT_TRACKER can catch the case.
>
>
> >
> > Otherwise bugs in subsystems not properly dismantling their kernel
> > socket at netns dismantle are next to impossible to track and fix.
> >
> > If anyone has time to implement this, feel free to submit patches.
> >
> > Thanks.