linux-kernel - Re: [PATCH next] vhost_task: after freeing vhost_task it should not be accessed in vhost_task

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Date: Wed, 1 May 2024 10:57:38 -0500
From: Mike Christie <michael.christie@...cle.com>
To: Hillf Danton <hdanton@...a.com>, "Michael S. Tsirkin" <mst@...hat.com>
Cc: Edward Adam Davis <eadavis@...com>,
        syzbot+98edc2df894917b3431f@...kaller.appspotmail.com,
        jasowang@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        virtualization@...ts.linux.dev
Subject: Re: [PATCH next] vhost_task: after freeing vhost_task it should not
 be accessed in vhost_task_fn

On 5/1/24 2:50 AM, Hillf Danton wrote:
> On Wed, 1 May 2024 02:01:20 -0400 Michael S. Tsirkin <mst@...hat.com>
>>
>> and then it failed testing.
>>
> So did my patch [1] but then the reason was spotted [2,3]
> 
> [1] https://lore.kernel.org/lkml/20240430110209.4310-1-hdanton@sina.com/
> [2] https://lore.kernel.org/lkml/20240430225005.4368-1-hdanton@sina.com/
> [3] https://lore.kernel.org/lkml/000000000000a7f8470617589ff2@google.com/

Just to make sure I understand the conclusion.

Edward's patch that just swaps the order of the calls:

https://lore.kernel.org/lkml/tencent_546DA49414E876EEBECF2C78D26D242EE50A@qq.com/

fixes the UAF. I tested the same in my setup. However, when you guys tested it
with sysbot, it also triggered a softirq/RCU warning.

The softirq/RCU part of the issue is fixed with this commit:

https://lore.kernel.org/all/20240427102808.29356-1-qiang.zhang1211@gmail.com/

commit 1dd1eff161bd55968d3d46bc36def62d71fb4785
Author: Zqiang <qiang.zhang1211@...il.com>
Date:   Sat Apr 27 18:28:08 2024 +0800

    softirq: Fix suspicious RCU usage in __do_softirq()

The problem was that I was testing with -next master which has that patch.
It looks like you guys were testing against bb7a2467e6be which didn't have
the patch, and so that's why you guys still hit the softirq/RCU issue. Later
when you added that patch to your patch, it worked with syzbot.

So is it safe to assume that the softirq/RCU patch above will be upstream
when the vhost changes go in or is there a tag I need to add to my patches?