From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752361AbdKFLZc (ORCPT ); Mon, 6 Nov 2017 06:25:32 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:39291 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751956AbdKFLZb (ORCPT ); Mon, 6 Nov 2017 06:25:31 -0500 Date: Mon, 6 Nov 2017 11:25:08 +0000 From: Jamie Iles To: Dmitry Vyukov Cc: Oleg Nesterov , syzbot , Andrew Morton , Arvind Yadav , Mark Brown , "Eric W. Biederman" , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , jamie.iles@oracle.com, LKML , "Martin K. Petersen" , mchehab@kernel.org, Ingo Molnar , mpe@ellerman.id.au, syzkaller-bugs@googlegroups.com, Al Viro , Kyle Huey , Kees Cook Subject: Re: WARNING in task_participate_group_stop Message-ID: <20171106112508.lun6eftpj5icnvdy@cedar> References: <94eb2c058c80ea49ed055cc8695e@google.com> <20171031163451.GA30223@redhat.com> <20171102170138.GA13663@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dmitry, On Mon, Nov 06, 2017 at 12:02:19PM +0100, Dmitry Vyukov wrote: > On Thu, Nov 2, 2017 at 6:01 PM, Oleg Nesterov wrote: > > On 11/01, Dmitry Vyukov wrote: > >> > >> On Tue, Oct 31, 2017 at 7:34 PM, Oleg Nesterov wrote: > >> > Hmm. I do not see reproducer in this email... > >> > >> Ah, sorry. You can see full thread with attachments here: > >> https://groups.google.com/forum/#!topic/syzkaller-bugs/EUmYZU4m5gU > > > > Heh. I can't say I enjoyed reading the reproducer ;) > > > >> >> > WARNING: CPU: 0 PID: 1 at kernel/signal.c:340 > >> >> > task_participate_group_stop+0x1ce/0x230 kernel/signal.c:340 > >> >> > Kernel panic - not syncing: panic_on_warn set ... > >> >> > > >> >> > CPU: 0 PID: 1 Comm: init Not tainted 4.13.0-mm1+ #5 > >> > > >> > So this is init process with SIGNAL_UNKILLABLE flag set. And I hope it has > >> > the pending SIGKILL, otherwise there is something else. > > > > From repro.c > > > > 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. > > > > But how *(uint32_t*)0x20f9cffc can be 1 ? > > > > line 108 r[6] = syscall(__NR_fcntl, r[1], 0x10ul, 0x20f9cff8ul); > > > > this is F_GETOWN_EX, addr = 0x20f9cff8 == 0x20f9cffc + 4, so if fcntl() > > actually succeeds then r[7] == f_owner_ex->pid. > > > > It _can_ be 1, but the reproducer doesn't work for me. If you can reproduce, > > could you try the patch below? > > Hi, > > I would like to understand why you were not able to reproduce it. I > won't be sitting here all the time, and we are tracking hundreds of > bugs across different linux kernels and other OSes, so it's > problematic to do any extensive work on all of them. That's why we try > to provide reproducers. > > I've just tried the repro on the latest upstream > (39dae59d66acd86d1de24294bd2f343fd5e7a625) and it triggered the > WARNING within a second. > Did you use the config provided? Did you use qemu or real hardware? > Can you try in qemu (with -smp>1)? I'm unable to reproduce the warning in qemu with SMP (on a 32 CPU VM). 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 [ 45.023821] ? __warn+0x1d9/0x1d9 [ 45.024206] ? _raw_write_unlock_irq+0x27/0x70 [ 45.024705] do_exit+0x27ac/0x2f60 [ 45.025101] ? trace_hardirqs_on+0xd/0x10 [ 45.025551] ? _raw_spin_unlock_irq+0x27/0x70 [ 45.026034] ? mm_update_next_owner+0x640/0x640 [ 45.026540] ? get_signal+0x675/0x1520 [ 45.026971] ? recalc_sigpending+0x72/0x90 [ 45.027464] ? lock_downgrade+0x820/0x820 [ 45.027916] ? __dequeue_signal+0x640/0x640 [ 45.028388] ? _raw_spin_unlock_irq+0x27/0x70 [ 45.028877] do_group_exit+0x108/0x330 [ 45.029297] get_signal+0x61a/0x1520 [ 45.031144] do_signal+0x8d/0x1a10 [ 45.031531] ? trace_hardirqs_on_caller+0x442/0x5c0 [ 45.032105] ? trace_hardirqs_on+0xd/0x10 [ 45.032571] ? setup_sigcontext+0x7d0/0x7d0 [ 45.033071] ? ep_poll_readyevents_proc+0xa0/0xa0 [ 45.033619] ? rw_verify_area+0xe5/0x2b0 [ 45.034063] ? SyS_timerfd_settime+0xe5/0x140 [ 45.034551] ? exit_to_usermode_loop+0x45/0x230 [ 45.035065] exit_to_usermode_loop+0x16a/0x230 [ 45.035599] ? trace_hardirqs_on_caller+0x442/0x5c0 [ 45.036833] syscall_return_slowpath+0x310/0x3d0 [ 45.038547] entry_SYSCALL_64_fastpath+0xbc/0xbe [ 45.039779] RIP: 0033:0x7fd80a914133 [ 45.040215] RSP: 002b:00007fff313d0858 EFLAGS: 00000246 ORIG_RAX: 00000000000000e8 [ 45.041683] RAX: fffffffffffffffc RBX: 000055f47338c050 RCX: 00007fd80a914133 [ 45.042451] RDX: 000000000000003d RSI: 00007fff313d0860 RDI: 0000000000000004 [ 45.043307] RBP: 00007fff313d0c50 R08: 00007fff313d0860 R09: 8258efee6555c1f9 [ 45.044107] R10: 00000000ffffffff R11: 0000000000000246 R12: 00007fff313d0860 [ 45.045011] R13: ffffffffffffffff R14: 00007fff313d0c70 R15: 0000000000000001 [ 45.046217] Kernel Offset: disabled [ 45.046615] Rebooting in 86400 seconds.. Running the same reproducer as an unprivileged user does not have any effect - the system continues to run fine without any warning or panic. Thanks, Jamie