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

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Date:   Wed, 21 Nov 2018 18:16:50 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Andrei Vagin <avagin@...il.com>
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 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).

> --- 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.