linux-kernel - Re: general protection fault in tomoyo_socket_sendmsg

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Message-ID: <92a4c6ae-172d-91cb-b89e-8eb857fdfb3a@linuxfoundation.org>
Date:   Wed, 10 Feb 2021 12:29:15 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+95ce4b142579611ef0a9@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        syzkaller-bugs@...glegroups.com,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: general protection fault in tomoyo_socket_sendmsg_permission

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