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From: Thomas Gleixner <tglx@kernel.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
 Hyunwoo Kim <imv4bel@gmail.com>, Christian Brauner <brauner@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>, John Stultz <jstultz@google.com>,
 Ingo Molnar <mingo@kernel.org>, Alexander Viro <viro@zeniv.linux.org.uk>,
 "Eric W. Biederman" <ebiederm@xmission.com>, stable@vger.kernel.org
Subject: Re: [patch 1/8] signal: Prevent exec() race
In-Reply-To: <apvJ0PO7DJnh1JHS@pavilion.home>
References: <20260904112100.683893401@kernel.org>
 <20260904112202.074391651@kernel.org> <apqs6wgDtpdLI-k8@redhat.com>
 <87zexw5exv.ffs@fw13> <apvJ0PO7DJnh1JHS@pavilion.home>
Date: Sat, 05 Sep 2026 13:22:39 +0200
Message-ID: <87o6ec54e8.ffs@fw13>
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On Sat, Sep 05 2026 at 09:50, Frederic Weisbecker wrote:
> Le Sat, Sep 05, 2026 at 09:34:52AM +0200, Thomas Gleixner a =C3=A9crit :
>> On Fri, Sep 04 2026 at 13:35, Oleg Nesterov wrote:
>> > Thomas, I can't read this series today, will try on Weekend.
>> >
>> > But you didn't reply to
>> > https://lore.kernel.org/all/apgHJj0qH7HlAXKO@redhat.com/
>> > Let me quote that email here:
>> >
>> > 	OK... lets suppose the exiting task T passes exit_signals().
>> >
>> > 	Suppose we have an "ignored" timer tmr. Another sub-thread calls
>> > 	do_sigaction() -> posixtimer_sig_unignore() and finds that tmr
>> > 	in ->ignored_posix_timers list.
>> >
>> > 	But posixtimer_queue_sigqueue() doesn't check PF_EXITING, I guess
>> > 	it should check it too?
>>=20
>> From the patch:
>>=20
>> @@ -1990,6 +2004,9 @@ void posixtimer_send_sigqueue(struct k_i
>> 	if (!likely(lock_task_sighand(t, &flags)))
>> 		return;
>>=20
>> +	if (unlikely(tmr->it_pid_type =3D=3D PIDTYPE_PID && (t->flags & PF_EXI=
TING)))
>> +		goto unlock;
>> +
>
> But posixtimer_sig_unignore() calls directly posixtimer_queue_sigqueue(),=
 not
> posixtimer_send_sigqueue().

I obviously can't read.

> However posixtimer_queue_sigqueue() -> complete_signal() -> wants_signal()
> checks PF_EXITING and complete_signal() then just drops it.
>
> Ah but doesn't that leak a refcount drop? Looks like the PF_EXITING check=
 should
> indeed move to posixtimer_get_target().

Again. get_target() is not protected by sighand lock when called in
posxtimer_send_sigqueue().

Let me stare at it some more.