linux-kernel - Re: [PATCH] ptrace: take into account saved_sigmask in PTRACE

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Date:   Sat, 2 Feb 2019 02:04:40 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] ptrace: take into account saved_sigmask in
 PTRACE_{GET,SET}SIGMASK

On Wed, Nov 21, 2018 at 06:16:50PM -0800, Andrew Morton wrote:
> On Mon, 19 Nov 2018 22:06:16 -0800 Andrei Vagin <avagin@...il.com> wrote:
> 
> > There are a few system calls (pselect, ppoll, etc) which replace a task
> > sigmask while they are running in a kernel-space
> > 
> > When a task calls one of these syscalls, the kernel saves a current
> > sigmask in task->saved_sigmask and sets a syscall sigmask.
> > 
> > On syscall-exit-stop, ptrace traps a task before restoring the
> > saved_sigmask, so PTRACE_GETSIGMASK returns the syscall sigmask and
> > PTRACE_SETSIGMASK does nothing, because its sigmask is replaced by
> > saved_sigmask, when the task returns to user-space.
> > 
> > This patch fixes this problem. PTRACE_GET_SIGMASK returns saved_sigmask
> > is it's set. PTRACE_SETSIGMASK drops the TIF_RESTORE_SIGMASK flag.
> 
> Looks good to me, but what would I know.  I'll await input from Eric
> and/or Oleg (please).

Hi Andrew,

What is your plan for this patch? In the ~akpm/mmotm/series, I see a
comment of waiting for ack from Oleg.

Here was a feedback from Oleg:
https://www.spinics.net/lists/kernel/msg2972154.html

where he said: "Ok, I think the patch is fine".

Is it enough or should I convince him to send a "real" ack?

Thanks,
Andrei

> 
> > --- a/include/linux/sched/signal.h
> > +++ b/include/linux/sched/signal.h
> > @@ -417,10 +417,20 @@ static inline void set_restore_sigmask(void)
> >  	set_thread_flag(TIF_RESTORE_SIGMASK);
> >  	WARN_ON(!test_thread_flag(TIF_SIGPENDING));
> >  }
> > +
> > +static inline void clear_tsk_restore_sigmask(struct task_struct *tsk)
> > +{
> > +	clear_tsk_thread_flag(tsk, TIF_RESTORE_SIGMASK);
> > +}
> 
> How irritating is it that this file uses "task" 85 times and "tsk" 19
> times?  What did that gain us?  This patch worsens things.
> 
> Oh well.