From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: 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>,
jamie.iles@oracle.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: Thu, 2 Nov 2017 18:01:38 +0100 [thread overview]
Message-ID: <20171102170138.GA13663@redhat.com> (raw)
In-Reply-To: <CACT4Y+Yex9wRJc_5TV+7gGmkNq0twbkCwzoPJOKtr_eFPB=vPQ@mail.gmail.com>
On 11/01, Dmitry Vyukov wrote:
>
> On Tue, Oct 31, 2017 at 7:34 PM, Oleg Nesterov <oleg@redhat.com> 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?
Oleg.
diff --git a/kernel/signal.c b/kernel/signal.c
index 800a18f..7e15b56 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -78,7 +78,7 @@ static int sig_task_ignored(struct task_struct *t, int sig, bool force)
handler = sig_handler(t, sig);
if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
- handler == SIG_DFL && !force)
+ handler == SIG_DFL && !(force && sig_kernel_only(sig)))
return 1;
return sig_handler_ignored(handler, sig);
@@ -94,13 +94,15 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
return 0;
- if (!sig_task_ignored(t, sig, force))
- return 0;
-
/*
- * Tracers may want to know about even ignored signals.
+ * Tracers may want to know about even ignored signal unless it
+ * is SIGKILL which can't be reported anyway but can be ignored
+ * by SIGNAL_UNKILLABLE task.
*/
- return !t->ptrace;
+ if (t->ptrace && sig != SIGKILL)
+ return 0;
+
+ return sig_task_ignored(t, sig, force);
}
/*
@@ -929,9 +931,9 @@ static void complete_signal(int sig, struct task_struct *p, int group)
* then start taking the whole group down immediately.
*/
if (sig_fatal(p, sig) &&
- !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
+ !(signal->flags & SIGNAL_GROUP_EXIT) &&
!sigismember(&t->real_blocked, sig) &&
- (sig == SIGKILL || !t->ptrace)) {
+ (sig == SIGKILL || !p->ptrace)) {
/*
* This signal will be fatal to the whole group.
*/
next prev parent reply other threads:[~2017-11-02 17:01 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 [this message]
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
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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