From: Eric Dumazet <eric.dumazet@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
"David S. Miller" <davem@davemloft.net>
Cc: David Ahern <dsahern@gmail.com>, Julian Anastasov <ja@ssi.bg>,
Cong Wang <xiyou.wangcong@gmail.com>,
syzbot <syzbot+30209ea299c09d8785c9@syzkaller.appspotmail.com>,
ddstreet@ieee.org, dvyukov@google.com,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com,
Linus Torvalds <torvalds@linux-foundation.org>,
Mahesh Bandewar <maheshb@google.com>
Subject: Re: [PATCH] ipv4: Delete uncached routes upon unregistration of loopback device.
Date: Sat, 4 May 2019 13:24:07 -0400 [thread overview]
Message-ID: <ed916873-4d7d-43f3-07cf-028d3ef4177c@gmail.com> (raw)
In-Reply-To: <ab80de53-25b8-618b-4dcb-b732059f6f9c@i-love.sakura.ne.jp>
On 5/4/19 1:09 PM, Tetsuo Handa wrote:
> On 2019/05/05 0:56, Eric Dumazet wrote:>
>> Well, you have not fixed a bug, you simply made sure that whatever cpu is using the
>> routes you forcibly deleted is going to crash the host very soon (use-after-frees have
>> undefined behavior, but KASAN should crash most of the times)
>
> I confirmed that this patch survives "#syz test:" before submitting.
> But you know that this patch is deleting the route entry too early. OK.
>
>>
>> Please do not send patches like that with a huge CC list, keep networking patches
>> to netdev mailing list.
>
> If netdev people started working on this "minutely crashing bug" earlier,
> I would not have written a patch...
So, just that you know, we are working on bug fixes, and this is best effort.
It is not because _you_ want to fix a particular bug (out of hundreds)
that we need to stop everything and work full time on a particular bug.
And here the root cause of the problem is elsewhere. A dst is leaking somewhere,
and prevents the netns dismantle.
We had many dst leaks in the past, and they keep being added by new bugs.
>
>>
>> Mahesh has an alternative patch, adding a fake device that can not be dismantled
>> to make sure we fully intercept skbs sent through a dead route, instead of relying
>> on loopback dropping them later at some point.
>
> So, the reason to temporarily move the refcount is to give enough period
> so that the route entry is no longer used. But moving the refcount to a
> loopback device in a namespace was wrong. Is this understanding correct?
I believe you need spend more time on studying the networking code by yourself,
add tracing if you believe this could be useful to you and others.
>
> Compared to moving the refcount to the loopback device in the init namespace,
> the fake device can somehow drop the refcount moved via rt_flush_dev(), can't it?
>
The fake device wont ever disappear.
> Anyway, I'll wait for Mahesh.
>
next prev parent reply other threads:[~2019-05-04 17:24 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-15 18:50 unregister_netdevice: waiting for DEV to become free (2) syzbot
2018-08-15 20:28 ` syzbot
2018-08-15 20:41 ` Dmitry Vyukov
2018-08-20 4:31 ` syzbot
2018-08-20 12:55 ` Julian Anastasov
2018-08-21 5:40 ` Cong Wang
2018-08-22 4:11 ` Julian Anastasov
2019-04-15 13:36 ` Tetsuo Handa
2019-04-15 15:35 ` David Ahern
2019-04-21 20:41 ` Stephen Suryaputra
2019-04-22 14:58 ` David Ahern
2019-04-22 16:04 ` Eric Dumazet
2019-04-22 16:09 ` Eric Dumazet
2019-04-16 14:00 ` Tetsuo Handa
2019-04-26 13:43 ` Tetsuo Handa
2019-04-27 17:16 ` David Ahern
2019-04-27 22:33 ` Tetsuo Handa
2019-04-27 23:52 ` Eric Dumazet
2019-04-28 4:22 ` Tetsuo Handa
2019-04-28 15:04 ` Eric Dumazet
2019-04-29 18:34 ` David Ahern
2019-04-29 18:43 ` David Ahern
2019-05-01 13:38 ` Tetsuo Handa
2019-05-01 14:52 ` David Ahern
2019-05-01 16:16 ` Tetsuo Handa
2019-05-04 14:52 ` [PATCH] ipv4: Delete uncached routes upon unregistration of loopback device Tetsuo Handa
2019-05-04 15:56 ` Eric Dumazet
2019-05-04 17:09 ` Tetsuo Handa
2019-05-04 17:24 ` Eric Dumazet [this message]
2019-05-04 20:13 ` Julian Anastasov
2019-11-28 9:56 ` unregister_netdevice: waiting for DEV to become free (2) Tetsuo Handa
2019-11-29 5:54 ` Lukas Bulwahn
2019-11-29 6:51 ` Jouni Högander
2019-12-05 10:00 ` Jouni Högander
2019-12-05 11:00 ` Tetsuo Handa
2019-12-16 11:12 ` Tetsuo Handa
2019-12-17 7:08 ` Jouni Högander
2019-10-11 10:14 ` Tetsuo Handa
2019-10-11 15:12 ` Alexei Starovoitov
2019-10-16 10:34 ` Toke Høiland-Jørgensen
2019-11-15 9:43 ` Tetsuo Handa
2019-11-21 11:36 ` Toke Høiland-Jørgensen
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