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From: Tycho Andersen <tycho@tycho.ws>
To: Christian Brauner <christian@brauner.io>
Cc: ebiederm@xmission.com, linux-kernel@vger.kernel.org,
	serge@hallyn.com, jannh@google.com, luto@kernel.org,
	akpm@linux-foundation.org, oleg@redhat.com, cyphar@cyphar.com,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, dancol@google.com,
	timmurray@google.com, linux-man@vger.kernel.org,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v1 2/2] signal: add procfd_signal() syscall
Date: Mon, 19 Nov 2018 15:39:54 -0700
Message-ID: <20181119223954.GA4992@cisco> (raw)
In-Reply-To: <20181119103241.5229-3-christian@brauner.io>

On Mon, Nov 19, 2018 at 11:32:39AM +0100, Christian Brauner wrote:
>
> +/**
> + *  sys_procfd_signal - send a signal to a process through a process file
> + *                      descriptor
> + *  @fd: the file descriptor of the process
> + *  @sig: signal to be sent
> + *  @info: the signal info
> + *  @flags: future flags to be passed
> + */
> +SYSCALL_DEFINE4(procfd_signal, int, fd, int, sig, siginfo_t __user *, info,
> +		int, flags)
> +{

Can I just register an objection here that I think using a syscall
just for this is silly?

My understanding is that the concern is that some code might do:

unknown_fd = recv_fd();
ioctl(unknown_fd, SOME_IOCTL, NULL); // where SOME_IOCTL == PROC_FD_KILL
// whoops, unknown_fd was a procfd and we killed a task!

In my experience when writing fd sending/receiving code, the sender and
receiver are fairly tightly coupled. Has anyone ever actually fixed a
bug where they had an fd that they lost track of what "type" it was
and screwed up like this? It seems completely theoretical to me.

The ioctl() approach has the benefit of being extensible. Adding a
syscall means that everyone has to do all the boilerplate for each new
pid op in the kernel, arches, libc, strace, etc.

Tycho

  parent reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 10:32 [PATCH v1 0/2] proc: allow signaling processes via file descriptors Christian Brauner
2018-11-19 10:32 ` [PATCH v1 1/2] proc: get process file descriptor from /proc/<pid> Christian Brauner
2018-11-19 15:32   ` Andy Lutomirski
2018-11-19 18:20     ` Christian Brauner
2018-11-19 10:32 ` [PATCH v1 2/2] signal: add procfd_signal() syscall Christian Brauner
2018-11-19 15:45   ` Andy Lutomirski
2018-11-19 15:57     ` Daniel Colascione
2018-11-19 18:39     ` Christian Brauner
2018-11-19 15:59   ` Daniel Colascione
2018-11-19 18:29     ` Christian Brauner
2018-11-19 19:02       ` Eric W. Biederman
2018-11-19 19:31         ` Christian Brauner
2018-11-19 19:39           ` Daniel Colascione
2018-11-19 17:10   ` Eugene Syromiatnikov
2018-11-19 18:23     ` Christian Brauner
2018-11-19 17:14   ` Eugene Syromiatnikov
2018-11-19 20:28   ` Aleksa Sarai
2018-11-19 20:55     ` Christian Brauner
2018-11-19 21:13       ` Christian Brauner
2018-11-19 21:18       ` Aleksa Sarai
2018-11-19 21:20         ` Christian Brauner
2018-11-19 21:21         ` Christian Brauner
2018-11-19 21:25           ` Aleksa Sarai
2018-11-19 21:26           ` Daniel Colascione
2018-11-19 21:36             ` Aleksa Sarai
2018-11-19 21:37             ` Christian Brauner
2018-11-19 21:41               ` Daniel Colascione
2018-11-20  4:59                 ` Eric W. Biederman
2018-11-20 10:31                   ` Christian Brauner
2018-11-21 21:39                     ` Serge E. Hallyn
2018-11-19 21:23         ` Aleksa Sarai
2018-11-22  7:41           ` Serge E. Hallyn
2018-11-19 22:39   ` Tycho Andersen [this message]
2018-11-19 22:49     ` Daniel Colascione
2018-11-19 23:07       ` Tycho Andersen
2018-11-20  0:27         ` Andy Lutomirski
2018-11-20  0:32           ` Christian Brauner
2018-11-20  0:34             ` Andy Lutomirski
2018-11-20  0:49           ` Daniel Colascione
2018-11-22  7:48     ` Serge E. Hallyn
2018-11-19 23:35   ` kbuild test robot
2018-11-19 23:37   ` kbuild test robot
2018-11-19 23:45     ` Christian Brauner
2018-11-28 21:45   ` Joey Pabalinas
2018-11-28 22:05     ` Christian Brauner
2018-11-28 23:02       ` Joey Pabalinas
2018-11-19 10:32 ` [PATCH] procfd_signal.2: document procfd_signal syscall Christian Brauner
2018-11-20 13:29   ` Michael Kerrisk (man-pages)
2018-11-28 20:59   ` Florian Weimer
2018-11-28 21:12     ` Christian Brauner

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