Re: KASAN: use-after-free Read in tcp_write_timer_handler

From: Eric Dumazet <edumazet@google.com>
To: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: bpf@vger.kernel.org, davem@davemloft.net, dsahern@kernel.org,
	kuba@kernel.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, pabeni@redhat.com, threeearcat@gmail.com,
	yoshfuji@linux-ipv6.org
Subject: Re: KASAN: use-after-free Read in tcp_write_timer_handler
Date: Wed, 5 Apr 2023 21:47:54 +0200	[thread overview]
Message-ID: <CANn89iJeHFb8VnFPUq4-d+jzAO6XKiSQhaPsPFY98wjH0Yx1Lw@mail.gmail.com> (raw)
In-Reply-To: <20230405194143.15708-1-kuniyu@amazon.com>

On Wed, Apr 5, 2023 at 9:42 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
>
> From:   Eric Dumazet <edumazet@google.com>
> Date:   Wed, 5 Apr 2023 13:28:16 +0200
> > On Wed, Apr 5, 2023 at 12:41 PM Dae R. Jeong <threeearcat@gmail.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@google.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.