Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: general protection fault in tomoyo_socket_sendmsg_permission
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Hillf Danton <hdanton@sina.com>,
        syzbot <syzbot+95ce4b142579611ef0a9@syzkaller.appspotmail.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>,
        Valentina Manea <valentina.manea.m@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        syzkaller-bugs@googlegroups.com,
        Shuah Khan <skhan@linuxfoundation.org>
References: <000000000000647eff05b3f7e0d4@google.com>
 <20201113120055.11748-1-hdanton@sina.com>
 <5f71e0c1-d387-6d72-d8e4-edb11cf57f72@linuxfoundation.org>
 <ea4028b7-53f2-aeaf-76e7-69874efcdec5@I-love.SAKURA.ne.jp>
 <2b70d360-a293-4acb-ea6c-2badda5e8b8b@linuxfoundation.org>
 <9bdd3f10-bddb-bd87-d7ad-b4b706477006@i-love.sakura.ne.jp>
 <6b8da36f-a994-7604-77f4-52e29434605f@linuxfoundation.org>
 <5f9ec159-77d8-ffba-21d1-2810e059f998@i-love.sakura.ne.jp>
 <a06093f1-22b3-7d72-bc6c-f99f4e0d0de9@linuxfoundation.org>
 <40617d66-1334-13a0-de9b-bd7cc1155ce5@i-love.sakura.ne.jp>
 <43d8d6bf-53f3-11e6-894d-c257f7f4bd07@linuxfoundation.org>
 <4368349b-fc0c-6da3-a502-2733f953d271@i-love.sakura.ne.jp>
From:   Shuah Khan <skhan@linuxfoundation.org>
Message-ID: <92a4c6ae-172d-91cb-b89e-8eb857fdfb3a@linuxfoundation.org>
Date:   Wed, 10 Feb 2021 12:29:15 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.1
MIME-Version: 1.0
In-Reply-To: <4368349b-fc0c-6da3-a502-2733f953d271@i-love.sakura.ne.jp>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2/10/21 12:07 PM, Tetsuo Handa wrote:
> On 2021/02/11 3:17, Shuah Khan wrote:
>> I am looking to understand the syzbot configuration and a reproducer
>> to be able to debug and fix the problem. How is syzbot triggering the
>> vhci_hcd attach and detach sequence?
> 
> I don't know. I'm waiting for syzbot to reproduce the problem on linux-next
> with https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/usb/usbip?id=f1bdf414e7dd0cbc26460425719fc3ea479947a2 .
> 
>>
>> This helps me determine all these fix suggestions that are coming in
>> are fixes or papering over a real problem.
> 
> What are these fix suggestions?
> 
> "general protection fault in tomoyo_socket_sendmsg_permission" is a NULL pointer
> dereference which can happen if vhci_device_reset() and/or vhci_device_init()
> (which does vdev->ud.tcp_socket = NULL;) were unexpectedly called. There is no
> reproducer, and (as far as I know) no fix suggestion.
> 
Right. I would like to get a clear understanding of how this condition
is triggered. I am not saying this isn't a problem. Understanding how
it is triggered helps find the best fix.

> "KASAN: null-ptr-deref Write in vhci_shutdown_connection" is an ERR_PTR(-EINTR)
> pointer dereference which can happen if kthread_create() was SIGKILLed. There is
> a reproducer, and https://lkml.kernel.org/r/20210205135707.4574-1-penguin-kernel@I-love.SAKURA.ne.jp
> is a fix suggestion.
> 

This is a good find. I already replied to the thread to send a complete
fix.

thanks,
-- Shuah