From: Oleg Nesterov <oleg@redhat.com>
To: Jamie Iles <jamie.iles@oracle.com>
Cc: "Dmitry Vyukov" <dvyukov@google.com>,
syzbot
<bot+c9f0eb0d2a5576ece331a767528e6b52b4ff1815@syzkaller.appspotmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Arvind Yadav" <arvind.yadav.cs@gmail.com>,
"Mark Brown" <broonie@kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
mchehab@kernel.org, "Ingo Molnar" <mingo@kernel.org>,
mpe@ellerman.id.au, syzkaller-bugs@googlegroups.com,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Kyle Huey" <me@kylehuey.com>,
"Kees Cook" <keescook@chromium.org>
Subject: Re: WARNING in task_participate_group_stop
Date: Mon, 6 Nov 2017 15:31:38 +0100 [thread overview]
Message-ID: <20171106143138.GA17423@redhat.com> (raw)
In-Reply-To: <20171106112508.lun6eftpj5icnvdy@cedar>
On 11/06, Jamie Iles wrote:
>
> I'm unable to reproduce the warning in qemu with SMP (on a 32 CPU VM).
Neither me. Perhaps because I tried this test-case on the minimal system
with /bin/sh running as init process.
> Instead I get the following instant traceback which is different to what
> you report when run as root:
>
> [ 45.018469] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000013
> [ 45.018469]
> [ 45.019669] CPU: 19 PID: 1 Comm: systemd Not tainted 4.14.0-rc8 #7
> [ 45.021094] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
> [ 45.022768] Call Trace:
> [ 45.023076] dump_stack+0x12e/0x188
> [ 45.023481] panic+0x1e4/0x417
This is fine and hopefully confirms the theory. let me quote my previous email:
line 111 r[8] = syscall(__NR_ptrace, 0x10ul, r[7]);
this is PTRACE_ATTACH
line 115 syscall(__NR_ptrace, 0x4200ul, r[7], 0x40000012ul, 0x100012ul);
this is PTRACE_SETOPTIONS and "data" includes PTRACE_O_EXITKILL.
r[7] is initialized at
line 110 r[7] = *(uint32_t*)0x20f9cffc;
so if it is eq to 1 then it can attach to init and in this case the problem
can be explained by the wrong SIGNAL_UNKILLABLE/SIGKILL logic.
So, if it is eq to 1 then init will be killed after the child process created
by loop() function exits (see PTRACE_O_EXITKILL above).
This is correct, only the warning is not.
For example, this command does ptrace(PTRACE_SEIZE, 1,0, PTRACE_O_EXITKILL)
# perl -e 'syscall 101, 0x4206, 1, 0, 0x100000'
and crashes the kernel the same way, this is correct.
Oleg.
next prev parent reply other threads:[~2017-11-06 14:31 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-30 19:12 WARNING in task_participate_group_stop syzbot
2017-10-30 19:20 ` Dmitry Vyukov
2017-10-31 16:34 ` Oleg Nesterov
2017-11-01 5:55 ` Dmitry Vyukov
2017-11-02 17:01 ` Oleg Nesterov
2017-11-06 11:02 ` Dmitry Vyukov
2017-11-06 11:25 ` Jamie Iles
2017-11-06 11:56 ` Dmitry Vyukov
2017-11-06 12:26 ` Jamie Iles
2017-11-06 14:31 ` Oleg Nesterov [this message]
2017-11-07 17:31 ` Dmitry Vyukov
-- strict thread matches above, loose matches on Subject: below --
2015-11-02 13:25 Dmitry Vyukov
2015-11-02 15:13 ` Oleg Nesterov
2015-11-02 14:21 ` Dmitry Vyukov
2015-11-02 15:33 ` Oleg Nesterov
2015-11-02 16:36 ` Oleg Nesterov
2015-11-02 18:06 ` Oleg Nesterov
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