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From: Pavel Machek <pavel@ucw.cz>
To: Daniel Colascione <dancol@google.com>
Cc: linux-kernel@vger.kernel.org, timmurray@google.com,
	joelaf@google.com, surenb@google.com
Subject: Re: [RFC PATCH] Implement /proc/pid/kill
Date: Tue, 13 Nov 2018 00:13:36 +0100	[thread overview]
Message-ID: <20181112231336.GA19782@amd> (raw)
In-Reply-To: <20181029221037.87724-1-dancol@google.com>

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Hi!

> Add a simple proc-based kill interface. To use /proc/pid/kill, just
> write the signal number in base-10 ASCII to the kill file of the
> process to be killed: for example, 'echo 9 > /proc/$$/kill'.
> 
> Semantically, /proc/pid/kill works like kill(2), except that the
> process ID comes from the proc filesystem context instead of from an
> explicit system call parameter. This way, it's possible to avoid races
> between inspecting some aspect of a process and that process's PID
> being reused for some other process.

I'd really prefer this to use a new syscall, taking directory fd as an
argument. Various security solutions (seccomp, chromium sandbox,
ptrace/subterfugue) could be pretty surprised what write to a file is
doing...

> With /proc/pid/kill, it's possible to write a proper race-free and
> safe pkill(1). An approximation follows. A real program might use
> openat(2), having opened a process's /proc/pid directory explicitly,
> with the directory file descriptor serving as a sort of "process
> handle".

Actually.. if you open /proc/123 directory, is pid 123 still going to
be reused?

If so... could we simply block reuse of that pid as long as directory
is open? It would solve the race w/o new file and w/o new syscall...

Good luck,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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      parent reply	other threads:[~2018-11-12 23:13 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-29 22:10 [RFC PATCH] Implement /proc/pid/kill Daniel Colascione
2018-10-30  3:21 ` Joel Fernandes
2018-10-30  8:50   ` Daniel Colascione
2018-10-30 10:39     ` Christian Brauner
2018-10-30 10:40       ` Christian Brauner
2018-10-30 10:48         ` Daniel Colascione
2018-10-30 11:04           ` Christian Brauner
2018-10-30 11:12             ` Daniel Colascione
2018-10-30 11:19               ` Christian Brauner
2018-10-31  5:00                 ` Eric W. Biederman
2018-10-30 17:01     ` Joel Fernandes
2018-10-30  5:00 ` Aleksa Sarai
2018-10-30  9:05   ` Daniel Colascione
2018-10-30 20:45     ` Aleksa Sarai
2018-10-30 21:42       ` Joel Fernandes
2018-10-30 22:23         ` Aleksa Sarai
2018-10-30 22:33           ` Joel Fernandes
2018-10-30 22:49             ` Aleksa Sarai
2018-10-31  0:42               ` Joel Fernandes
2018-10-31  1:59                 ` Daniel Colascione
2018-10-30 23:10             ` Daniel Colascione
2018-10-30 23:23               ` Christian Brauner
2018-10-30 23:55                 ` Daniel Colascione
2018-10-31  2:56                 ` Aleksa Sarai
2018-10-31  4:24                   ` Joel Fernandes
2018-11-01 20:40                     ` Joel Fernandes
2018-11-02  9:46                       ` Christian Brauner
2018-11-02 14:34                         ` Serge E. Hallyn
2018-10-31  0:57               ` Joel Fernandes
2018-10-31  1:56                 ` Daniel Colascione
2018-10-31  4:47   ` Eric W. Biederman
2018-10-31  4:44 ` Eric W. Biederman
2018-10-31 12:44   ` Oleg Nesterov
2018-10-31 13:27     ` Daniel Colascione
2018-10-31 15:10       ` Oleg Nesterov
2018-10-31 15:16         ` Daniel Colascione
2018-10-31 15:49           ` Oleg Nesterov
2018-11-01 11:53       ` David Laight
2018-11-01 15:50         ` Daniel Colascione
2018-10-31 14:37 ` [PATCH v2] " Daniel Colascione
2018-10-31 15:05   ` Joel Fernandes
2018-10-31 17:33     ` Aleksa Sarai
2018-10-31 21:47       ` Joel Fernandes
2018-10-31 15:59 ` [PATCH v3] " Daniel Colascione
2018-10-31 17:54   ` Tycho Andersen
2018-10-31 18:00     ` Daniel Colascione
2018-10-31 18:17       ` Tycho Andersen
2018-10-31 19:33         ` Daniel Colascione
2018-10-31 20:06           ` Tycho Andersen
2018-11-01 11:33           ` David Laight
2018-11-12  1:19             ` Eric W. Biederman
2018-10-31 16:22 ` [RFC PATCH] " Jann Horn
2018-11-01  4:53   ` Andy Lutomirski
2018-11-12 23:13 ` Pavel Machek [this message]

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