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From: Aleksa Sarai <cyphar@cyphar.com>
To: Christian Brauner <christian@brauner.io>
Cc: Florian Weimer <fweimer@redhat.com>,
	ebiederm@xmission.com, linux-kernel@vger.kernel.org,
	serge@hallyn.com, jannh@google.com, luto@kernel.org,
	akpm@linux-foundation.org, oleg@redhat.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 v2] signal: add procfd_signal() syscall
Date: Tue, 4 Dec 2018 17:03:54 +1100
Message-ID: <20181204060354.bozjmjn24sw3axav@yavin> (raw)
In-Reply-To: <20181203180224.fkvw4kajtbvru2ku@brauner.io>

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On 2018-12-03, Christian Brauner <christian@brauner.io> wrote:
> > > As I pointed out in another mail my I is to make this work by using
> > > file descriptors for /proc/<pid>/task/<tid>.  I don't want this in the
> > > initial patchset though.  I prefer to slowly add those features once
> > > we have gotten the basic functionality in.
> > 
> > Do you want to land all this in one kernel release?  I wonder how
> > applications are supposed to discover kernel support if functionality is
> > split across several kernel releases.  If you get EINVAL or EBADF, it
> > may not be obvious what is going on.
> 
> Sigh, I get that but I really don't want to have to land this in one big
> chunk. I want this syscall to go in in a as soon as we can to fulfill
> the most basic need: having a way that guarantees us that we signal the
> process that we intended to signal.
> 
> The thread case is easy to implement on top of it. But I suspect we will
> quibble about the exact semantics for a long time. Even now we have been
> on multiple - justified - detrous. That's all pefectly fine and
> expected. But if we have the basic functionality in we have time to do
> all of that. We might even land it in the same kernel release still. I
> really don't want to come of as tea-party-kernel-conservative here but I
> have time-and-time again seen that making something fancy and cover ever
> interesting feature in one patchset takes a very very long time.
> 
> If you care about userspace being able to detect that case I can return
> EOPNOTSUPP when a tid descriptor is passed.

Personally, I'm +1 on -EOPNOTSUPP so we can get an MVP merged, and add
new features in later patches.

> > What happens if you use the new interface with an O_PATH descriptor?
> 
> You get EINVAL. When an O_PATH file descriptor is created the kernel
> will set file->f_op = &empty_fops at which point the check I added 
>         if (!proc_is_tgid_procfd(f.file))
>                 goto err;
> will fail. Imho this is correct behavior since technically signaling a
> struct pid is the equivalent of writing to a file and hence doesn't
> purely operate on the file descriptor level.

Not to mention that O_PATH file descriptors are a whole kettle of fish
when it comes to permission checking semantics.


-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-20 10:51 Christian Brauner
2018-11-20 10:51 ` [PATCH v2] procfd_signal.2: document procfd_signal syscall Christian Brauner
2018-11-22  8:00 ` [PATCH v2] signal: add procfd_signal() syscall Serge E. Hallyn
2018-11-22  8:23 ` Aleksa Sarai
2018-11-28 14:05 ` Arnd Bergmann
2018-11-29 12:28 ` Florian Weimer
2018-11-29 16:54   ` Andy Lutomirski
2018-11-29 19:16     ` Christian Brauner
2018-11-29 19:22       ` Andy Lutomirski
2018-11-29 19:55         ` Christian Brauner
2018-11-29 20:14           ` Andy Lutomirski
2018-11-29 21:02             ` Arnd Bergmann
2018-11-29 21:35               ` Christian Brauner
2018-11-29 21:40                 ` Arnd Bergmann
2018-11-30  2:40                   ` Aleksa Sarai
2018-12-01  1:25                   ` Christian Brauner
2018-11-30  5:13               ` Eric W. Biederman
2018-11-30  6:56                 ` Christian Brauner
2018-11-30 11:41                   ` Arnd Bergmann
2018-11-30 16:35                     ` Andy Lutomirski
2018-11-30 21:57                       ` Christian Brauner
2018-11-30 22:09                       ` Arnd Bergmann
2018-11-30 22:26                         ` Christian Brauner
2018-11-30 23:05                           ` Daniel Colascione
2018-11-30 23:12                             ` Arnd Bergmann
2018-11-30 23:15                               ` Arnd Bergmann
2018-11-30 23:37                               ` Christian Brauner
2018-11-30 23:46                                 ` Andy Lutomirski
2018-12-01  1:20                                   ` Christian Brauner
2018-11-30 23:53                         ` Andy Lutomirski
2018-12-01  8:51                           ` Arnd Bergmann
2018-12-01  9:17                             ` Christian Brauner
2018-12-01 10:27                             ` Arnd Bergmann
2018-12-01 13:41                       ` Eric W. Biederman
2018-12-01 14:46                     ` Eric W. Biederman
2018-12-01 15:28                       ` Eric W. Biederman
2018-12-01 15:52                         ` Andy Lutomirski
2018-12-01 16:27                           ` Christian Brauner
2018-12-02  0:06                           ` Eric W. Biederman
2018-12-02  1:14                             ` Andy Lutomirski
2018-12-02  8:52                         ` Christian Brauner
2018-11-30 23:52   ` Christian Brauner
2018-12-02 10:03     ` Christian Brauner
2018-12-03 16:57       ` Florian Weimer
2018-12-03 18:02         ` Christian Brauner
2018-12-04  6:03           ` Aleksa Sarai [this message]
2018-12-04 12:55           ` Florian Weimer
2018-12-04 13:26             ` Christian Brauner
2018-12-06 18:54             ` Andy Lutomirski
2018-12-06 18:56               ` Florian Weimer
2018-12-06 19:03                 ` Christian Brauner
2018-12-25  5:32                   ` Lai Jiangshan
2018-12-25  7:11                     ` Lai Jiangshan
2018-12-25 12:07                       ` Aleksa Sarai

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