All of lore.kernel.org
 help / color / mirror / Atom feed
From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening
Date: Thu, 5 Sep 2019 17:21:57 +0200	[thread overview]
Message-ID: <20190905152156.GC18251@lenoir> (raw)
In-Reply-To: <alpine.DEB.2.21.1909051650030.1902@nanos.tec.linutronix.de>

On Thu, Sep 05, 2019 at 04:57:10PM +0200, Thomas Gleixner wrote:
> On Thu, 5 Sep 2019, Frederic Weisbecker wrote:
> > On Thu, Sep 05, 2019 at 02:03:39PM +0200, Thomas Gleixner wrote:
> > > Sysbot triggered an issue in the posix timer rework which was trivial to
> > > fix, but after running another test case I discovered that the rework broke
> > > the permission checks subtly. That's also a straightforward fix.
> > > 
> > > Though when staring at it I discovered that the permission checks for
> > > process clocks and process timers are completely bonkers. The only
> > > requirement is that the target PID is a group leader. Which means that any
> > > process can read the clocks and attach timers to any other process without
> > > priviledge restrictions.
> > > 
> > > That's just wrong because the clocks and timers can be used to observe
> > > behaviour and both reading the clocks and arming timers adds overhead and
> > > influences runtime performance of the target process.
> > 
> > Yeah I stumbled upon that by the past and found out the explanation behind
> > in old history: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/kernel/posix-cpu-timers.c?id=a78331f2168ef1e67b53a0f8218c70a19f0b2a4c
> > 
> > "This makes no constraint on who can see whose per-process clocks.  This
> > information is already available for the VIRT and PROF (i.e.  utime and stime)
> > information via /proc.  I am open to suggestions on if/how security
> > constraints on who can see whose clocks should be imposed."
> > 
> > I'm all for mitigating that, let's just hope that won't break some ABIs.
> 
> Well, reading clocks is one part of the issue. Arming timers on any process
> is a different story.

Exactly!

> 
> Also /proc/$PID access can be restricted nowadays. So that posic clock
> stuff should at least have exactly the same restrictions.

Yeah definetly.

> 
> Thanks,
> 
> 	tglx
> 

  reply	other threads:[~2019-09-05 15:22 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05 12:03 [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening Thomas Gleixner
2019-09-05 12:03 ` [patch 1/6] posix-cpu-timers: Always clear head pointer on dequeue Thomas Gleixner
2019-09-05 15:49   ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 2/6] posix-cpu-timers: Fix permission check regression Thomas Gleixner
2019-09-05 17:31   ` Frederic Weisbecker
2019-09-05 18:55     ` Thomas Gleixner
2019-09-05 21:15       ` [patch V2 " Thomas Gleixner
2019-09-09 15:13         ` Frederic Weisbecker
2019-09-10 11:18         ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2019-09-05 12:03 ` [patch 3/6] posix-cpu-timers: Restrict timer_create() permissions Thomas Gleixner
2019-09-21  0:44   ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 4/6] posix-cpu-timers: Restrict clock_gettime() permissions Thomas Gleixner
2019-09-23 13:39   ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 5/6] posix-cpu-timers: Sanitize thread clock permissions Thomas Gleixner
2019-09-05 12:21   ` Peter Zijlstra
2019-09-05 14:11     ` Thomas Gleixner
2019-09-23 14:03   ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 6/6] posix-cpu-timers: Make PID=0 and PID=self handling consistent Thomas Gleixner
2019-09-23 14:13   ` Frederic Weisbecker
2019-09-23 14:17     ` Thomas Gleixner
2019-09-05 14:48 ` [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening Frederic Weisbecker
2019-09-05 14:57   ` Thomas Gleixner
2019-09-05 15:21     ` Frederic Weisbecker [this message]
2019-09-05 20:32 ` Kees Cook
2019-09-05 21:13   ` Thomas Gleixner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190905152156.GC18251@lenoir \
    --to=frederic@kernel.org \
    --cc=fweisbec@gmail.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.