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From: Christian Brauner <christian@brauner.io>
To: Daniel Colascione <dancol@google.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Andy Lutomirski <luto@kernel.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Jann Horn <jannh@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Tim Murray <timmurray@google.com>,
	Kees Cook <keescook@chromium.org>,
	Jan Engelhardt <jengelh@inai.de>
Subject: Re: [PATCH] proc: allow killing processes via file descriptors
Date: Sun, 18 Nov 2018 22:30:23 +0100	[thread overview]
Message-ID: <20181118213021.24asgwkci3do6oby@brauner.io> (raw)
In-Reply-To: <20181118212336.53hh3qbjughrtc2l@brauner.io>

On Sun, Nov 18, 2018 at 10:23:36PM +0100, Christian Brauner wrote:
> On Sun, Nov 18, 2018 at 12:54:10PM -0800, Daniel Colascione wrote:
> > On Sun, Nov 18, 2018 at 12:43 PM, Christian Brauner
> > <christian@brauner.io> wrote:
> > > On Sun, Nov 18, 2018 at 01:28:41PM -0700, Andy Lutomirski wrote:
> > >>
> > >>
> > >> > On Nov 18, 2018, at 12:44 PM, Daniel Colascione <dancol@google.com> wrote:
> > >> >
> > >>
> > >> >
> > >> > That is, I'm proposing an API that looks like this:
> > >> >
> > >> > int process_kill(int procfs_dfd, int signo, const union sigval value)
> > >> >
> > >> > If, later, process_kill were to *also* accept process-capability FDs,
> > >> > nothing would break.
> > >>
> > >> Except that this makes it ambiguous to the caller as to whether their current creds are considered.  So it would need to be a different syscall or at least a flag.  Otherwise a lot of those nice theoretical properties go away.
> > >
> > > I can add a flag argument
> > > int process_signal(int procfs_dfd, int signo, siginfo_t *info, int flags)
> > > The way I see it process_signal() should be equivalent to kill(pid, signal) for now.
> > > That is siginfo_t is cleared and set to:
> > >
> > > info.si_signo = sig;
> > > info.si_errno = 0;
> > > info.si_code = SI_USER;
> > > info.si_pid = task_tgid_vnr(current);
> > > info.si_uid = from_kuid_munged(current_user_ns(), current_uid());
> > 
> > That makes sense. I just don't want to get into a situation where
> > callers feel that they *have* to use the PID-based APIs to send a
> > signal because process_kill doesn't offer some bit of functionality.
> 
> Yeah.
> 
> > 
> > Are you imagining something like requiring info t be NULL unless flags
> > contains some "I have a siginfo_t" value?
> 
> Well, I was actually thinking about something like:
> 
> /**
>  *  sys_process_signal - send a signal to a process trough 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(process_signal, int, fd, int, sig, siginfo_t __user *, info,
> 		int, flags)
> {
> 	struct pid *pid;
> 	struct fd *f;
> 	kernel_siginfo_t kinfo;
> 
> 	/* Do not allow users to pass garbage. */
> 	if (flags)
> 		return -EINVAL;
> 
> 	int ret = __copy_siginfo_from_user(sig, &kinfo, info);
> 	if (unlikely(ret))
> 		return ret;
> 
> 	/* For now, enforce that caller's creds are used. */
> 	kinfo.si_pid = task_tgid_vnr(current);
> 	kinfo.si_uid = from_kuid_munged(current_user_ns(), current_uid());
> 
> 	if (signal_impersonates_kernel(kinfo))
> 		return -EPERM;
> 
> 	f = fdget(fd);
> 	if (!f.file)
> 		return -EBADF;
> 
> 	pid = f.file->private_data;
> 	if (!pid)
> 		return -EBADF;
> 
> 	return kill_pid_info(sig, kinfo, pid);
> }

Just jotted this down here briefly. This will need an fput and so on
obvs.

> 
> > 
> > BTW: passing SI_USER to rt_sigqueueinfo *should* as long as the
> > passed-in si_pid and si_uid match what the kernel would set them to in
> > the kill(2) case. The whole point of SI_USER is that the recipient
> > knows that it can trust the origin information embedded in the
> > siginfo_t in the signal handler. If the kernel verifies that a signal
> > sender isn't actually lying, why not let people send SI_USER with
> > rt_sigqueueinfo?

  reply	other threads:[~2018-11-18 21:30 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-18 11:17 Christian Brauner
2018-11-18 13:59 ` Daniel Colascione
2018-11-18 15:38   ` Andy Lutomirski
2018-11-18 15:53     ` Daniel Colascione
2018-11-18 16:17       ` Andy Lutomirski
2018-11-18 16:29         ` Daniel Colascione
2018-11-18 17:13           ` Andy Lutomirski
2018-11-18 17:17             ` Daniel Colascione
2018-11-18 17:43               ` Eric W. Biederman
2018-11-18 17:45                 ` Andy Lutomirski
2018-11-18 17:56                 ` Daniel Colascione
2018-11-18 16:33         ` Randy Dunlap
2018-11-18 16:48           ` Daniel Colascione
2018-11-18 17:09             ` Andy Lutomirski
2018-11-18 17:24               ` Daniel Colascione
2018-11-18 17:42                 ` Andy Lutomirski
2018-11-18 17:51                   ` Daniel Colascione
2018-11-18 18:28                     ` Andy Lutomirski
2018-11-18 18:43                       ` Daniel Colascione
2018-11-18 19:05                         ` Aleksa Sarai
2018-11-18 19:44                           ` Daniel Colascione
2018-11-18 20:15                             ` Christian Brauner
2018-11-18 20:21                               ` Daniel Colascione
2018-11-18 20:28                             ` Andy Lutomirski
2018-11-18 20:32                               ` Daniel Colascione
2018-11-19  1:43                                 ` Andy Lutomirski
2018-11-18 20:43                               ` Christian Brauner
2018-11-18 20:54                                 ` Daniel Colascione
2018-11-18 21:23                                   ` Christian Brauner
2018-11-18 21:30                                     ` Christian Brauner [this message]
2018-11-19  0:31                                       ` Daniel Colascione
2018-11-19  0:40                                         ` Christian Brauner
2018-11-19  0:09                             ` Aleksa Sarai
2018-11-19  0:53                               ` Daniel Colascione
2018-11-19  1:16                                 ` Daniel Colascione
2018-11-19 16:13                       ` Dmitry Safonov
2018-11-19 16:26                         ` [PATCH] proc: allow killing processes via file descriptors (Larger pids) Eric W. Biederman
2018-11-19 16:27                         ` [PATCH] proc: allow killing processes via file descriptors Daniel Colascione
2018-11-19 20:21                           ` Aleksa Sarai
2018-11-19  2:47                   ` Al Viro
2018-11-19  3:01                     ` Andy Lutomirski
2018-11-18 17:41     ` Christian Brauner
2018-11-18 17:44       ` Andy Lutomirski
2018-11-18 18:07       ` Daniel Colascione
2018-11-18 18:15         ` Andy Lutomirski
2018-11-18 18:31           ` Daniel Colascione
2018-11-18 19:24         ` Christian Brauner
2018-11-19  0:08         ` Aleksa Sarai
2018-11-19  1:14           ` Daniel Colascione
2018-11-18 16:03 ` Daniel Colascione
2018-11-19 10:56 ` kbuild test robot
2018-11-19 14:15 ` David Laight
2018-11-19 15:49 ` Dave Martin

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