linux-kernel - RE: [PATCH] proc: allow killing processes via file descriptors

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Message-ID: <9a269517770e4881b92756d47f17a5fd@AcuMS.aculab.com>
Date:   Mon, 19 Nov 2018 14:15:31 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christian Brauner' <christian@...uner.io>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "serge@...lyn.com" <serge@...lyn.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "cyphar@...har.com" <cyphar@...har.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "dancol@...gle.com" <dancol@...gle.com>,
        "timmurray@...gle.com" <timmurray@...gle.com>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [PATCH] proc: allow killing processes via file descriptors

From: > Christian Brauner
> Sent: 18 November 2018 11:18
> 
> With this patch an open() call on /proc/<pid> will give userspace a handle
> to struct pid of the process associated with /proc/<pid>. This allows to
> maintain a stable handle on a process.

My 3c...

You need to add a version of fork() that returns an open fd to
/proc/pid to the parent.

Is it possible to overload fcntl() rather than ioctl() ?

More interestingly what about a 'unique pid' (eg the pid extended to
(say) 128 bits with a use count) that can be safely put into a /var/run/pid
file for a daemon and used later in a 'kill' that will only ever
reference the correct process.

	David

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