linux-kernel - Re: general protection fault in tomoyo_socket_sendmsg

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Message-ID: <4368349b-fc0c-6da3-a502-2733f953d271@i-love.sakura.ne.jp>
Date:   Thu, 11 Feb 2021 04:07:59 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Shuah Khan <skhan@...uxfoundation.org>,
        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
Subject: Re: general protection fault in tomoyo_socket_sendmsg_permission

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.

"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.