From: Vasiliy Kulikov <segoon@openwall.com>
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Sasha Levin <levinsasha928@gmail.com>,
khlebnikov@openvz.org, xemul@parallels.com,
Dave Jones <davej@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: c/r: broken locking when executing map_files
Date: Mon, 7 May 2012 00:21:32 +0400 [thread overview]
Message-ID: <20120506202132.GA6570@albatros> (raw)
In-Reply-To: <20120505193201.GA2500@moon>
On Sat, May 05, 2012 at 23:32 +0400, Cyrill Gorcunov wrote:
> On Sat, May 05, 2012 at 10:53:06PM +0400, Cyrill Gorcunov wrote:
> > On Sat, May 05, 2012 at 10:20:51PM +0400, Vasiliy Kulikov wrote:
> > > > - if (lock_trace(task))
> > > > + if (!ptrace_may_access(task, PTRACE_MODE_READ))
> > >
> > > Probably it will be better to change mutex_lock_killable() to
> > > mutex_lock_killable_nested() inside of lock_trace() instead of this change?
> > > It would keep the race-free check.
> >
> > Yup, if I'm not missing something SINGLE_DEPTH_NESTING should do the trick
> > for us. I'll test and report.
>
> Hmm, this doesn't work well, the mutex remanins killable so when one does
Does it show circular locking? It shouldn't block if it uses
mutex_lock+mutex_lock_nested.
> | [root@neptune ~]# /proc/self/map_files/400000-419000
>
> it sleeps forever until killed, which is not good I think. Vasiliy, could
> you remind me what exactly is problem if we use unlocked ptrace_may_access
> here?
There is a race between ptrace_may_access() and dname_to_vma_addr().
The target task may do exec() between these calls and
dname_to_vma_addr() will be called against a privileged task. This may
lead to a leak of task maps.
--
Vasily Kulikov
http://www.openwall.com - bringing security into open computing environments
next prev parent reply other threads:[~2012-05-06 20:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-02 17:23 c/r: broken locking when executing map_files Sasha Levin
2012-05-02 17:27 ` Cyrill Gorcunov
2012-05-03 17:31 ` Cyrill Gorcunov
2012-05-05 18:20 ` Vasiliy Kulikov
2012-05-05 18:53 ` Cyrill Gorcunov
2012-05-05 19:32 ` Cyrill Gorcunov
2012-05-06 20:21 ` Vasiliy Kulikov [this message]
2012-05-06 20:49 ` Cyrill Gorcunov
2012-05-11 17:56 ` Vasiliy Kulikov
2012-05-11 18:18 ` Cyrill Gorcunov
2012-05-02 17:34 ` Pavel Emelyanov
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