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From: Thomas Gleixner <tglx@linutronix.de>
To: "Jürg Billeter" <j@bitron.ch>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Eric Biederman <ebiederm@xmission.com>,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] prctl: add PR_[GS]ET_KILLABLE
Date: Mon, 30 Jul 2018 21:39:32 +0200 (CEST)
Message-ID: <alpine.DEB.2.21.1807302138580.1725@nanos.tec.linutronix.de> (raw)
In-Reply-To: <922baeb3d6d6387c480026fc3a6ca01d915f60a5.camel@bitron.ch>

[-- Attachment #1: Type: text/plain, Size: 1665 bytes --]

On Mon, 30 Jul 2018, Jürg Billeter wrote:

> On Mon, 2018-07-30 at 12:17 +0200, Oleg Nesterov wrote:
> > On 07/30, Jürg Billeter wrote:
> > > 
> > > This is required for job control in a shell that uses CLONE_NEWPID for
> > > child processes.
> > 
> > Could you explain in more details?
> 
> The SIGNAL_UNKILLABLE flag, which is implicitly set for tasks cloned
> with CLONE_NEWPID, has the effect of ignoring all signals (from
> userspace) if the corresponding handler is set to SIG_DFL. The only
> exceptions are SIGKILL and SIGSTOP and they are only accepted if raised
> from an ancestor namespace.
> 
> SIGINT, SIGQUIT and SIGTSTP are used in job control for ^C, ^\, ^Z.
> While a task with the SIGNAL_UNKILLABLE flag could install handlers for
> these signals, this is not sufficient to implement a shell that uses
> CLONE_NEWPID for child processes:
> 
>  * As SIGSTOP is ignored when raised from the SIGNAL_UNKILLABLE process
>    itself, I don't think it's possible to implement the stop action in
>    a custom SIGTSTP handler.
>  * Many applications do not install handlers for these signals and
>    thus, job control won't work properly with unmodified applications.
> 
> Job control in a shell is just an example. There are other scenarios,
> of course, where applications rely on the default actions as described
> in signal(7), and PID isolation may be useful. In my opinion, the
> kernel support for preventing accidental killing of the "init" process
> should really be optional and this new prctl provides this without
> breaking backward compatibility.

This makes sense and exactly that information needs to be in the changelog.

Thanks,

	tglx

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30  7:52 Jürg Billeter
2018-07-30 10:17 ` Oleg Nesterov
2018-07-30 19:32   ` Jürg Billeter
2018-07-30 19:39     ` Thomas Gleixner [this message]
2018-07-31  7:03 ` [PATCH v2] " Jürg Billeter
2018-07-31 14:39   ` Oleg Nesterov
2018-07-31 16:12     ` Jürg Billeter
2018-08-01 14:19       ` Oleg Nesterov
2018-08-03 10:15         ` Jürg Billeter
2018-08-03 12:14           ` Oleg Nesterov
2018-08-03 13:34           ` Eric W. Biederman
2018-08-03 14:39             ` Jürg Billeter
2018-07-31 16:26 ` [PATCH] " Jann Horn
2018-08-01  7:43   ` Jürg Billeter
2018-08-01  7:56     ` Jann Horn
2018-08-03 14:40 ` [PATCH v3 1/2] fork: do not rely on SIGNAL_UNKILLABLE for init check Jürg Billeter
2018-08-03 14:40   ` [PATCH v3 2/2] prctl: add PR_[GS]ET_KILLABLE Jürg Billeter
2018-09-06 22:42     ` Andrew Morton

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