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Message-ID: <20240418181821.GA26239@redhat.com>
Date: Thu, 18 Apr 2024 20:18:21 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>,
John Stultz <jstultz@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [patch V2 26/50] signal: Get rid of resched_timer logic
On 04/18, Oleg Nesterov wrote:
>
> On 04/11, Thomas Gleixner wrote:
> >
> > There is no reason for handing the *resched pointer argument through
> > several functions just to check whether the signal is related to a self
> > rearming posix timer.
>
> Agreed, these changes looks good to me.
I meant the intent.
But this is not simple, collect_signal() checks SIGQUEUE_PREALLOC exactly
because (iiuc) we need to ensure that SI_TIMER didn't come from userspace.
perhaps we should disallow SI_TIMER with _sys_private != 0 from userspace,
I dunno...
And I don't really understand the "not to be passed to user" comment in
include/uapi/asm-generic/siginfo.h. copy_siginfo_to_user() just copies
the whole kernel_siginfo.
Confused.
> But,
>
> > SI_TIMER is only used by the posix timer code and cannot be queued from
> > user space.
>
> Why? I think sigqueueinfo() can certainly use si_code = SI_TIMER, so
>
> > @@ -1011,6 +1001,9 @@ static int __send_signal_locked(int sig,
> >
> > lockdep_assert_held(&t->sighand->siglock);
> >
> > + if (WARN_ON_ONCE(!is_si_special(info) && info->si_code == SI_TIMER))
> > + return 0;
>
> this can be easily triggered by userspace and thus looks wrong.
>
> Oleg.
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