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From: Jann Horn <jann@thejh.net>
To: Ben Hutchings <ben@decadent.org.uk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Roland McGrath <roland@hack.frob.com>,
	Oleg Nesterov <oleg@redhat.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <james.l.morris@oracle.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Paul Moore <aul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Janis Danisevskis <jdanis@google.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric . Biederman" <ebiederm@xmission.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Benjamin LaHaise <bcrl@kvack.org>,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, security@kernel.org
Subject: Re: [PATCH 2/9] exec: turn self_exec_id into self_privunit_id
Date: Sun, 18 Sep 2016 21:08:10 +0200	[thread overview]
Message-ID: <20160918190810.GD17170@pc.thejh.net> (raw)
In-Reply-To: <20160918184507.GT10601@decadent.org.uk>

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On Sun, Sep 18, 2016 at 07:45:07PM +0100, Ben Hutchings wrote:
> On Sun, Sep 18, 2016 at 08:31:37PM +0200, Jann Horn wrote:
> > On Sun, Sep 18, 2016 at 07:13:27PM +0100, Ben Hutchings wrote:
> > > On Sun, 2016-09-18 at 17:05 +0200, Jann Horn wrote:
> > > > This ensures that self_privunit_id ("privilege unit ID") is only shared by
> > > > processes that share the mm_struct and the signal_struct; not just
> > > > spatially, but also temporally. In other words, if you do execve() or
> > > > clone() without CLONE_THREAD, you get a new privunit_id that has never been
> > > > used before.
> > > [...]
> > > > +void increment_privunit_counter(void)
> > > > +{
> > > > +	BUILD_BUG_ON(NR_CPUS > (1 << 16));
> > > > +	current->self_privunit_id = this_cpu_add_return(exec_counter, NR_CPUS);
> > > > +}
> > > [...]
> > > 
> > > This will wrap incorrectly if NR_CPUS is not a power of 2 (which is
> > > unusual but allowed).
> > 
> > If this wraps, hell breaks loose permission-wise - processes that have
> > no relationship whatsoever with each other will suddenly be able to ptrace
> > each other.
> > 
> > The idea is that it never wraps.
> 
> That's what I suspected, but wasn't sure.  In that case you can
> initialise each counter to U64_MAX/NR_CPUS*cpu and increment by
> 1 each time, which might be more efficient on some architectures.

Makes sense. Will do that!

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  reply	other threads:[~2016-09-18 19:08 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-18 15:05 [PATCH 0/9] Various fixes related to ptrace_may_access() Jann Horn
2016-09-18 15:05 ` [PATCH 1/9] exec: introduce cred_guard_light Jann Horn
2016-09-18 15:05 ` [PATCH 2/9] exec: turn self_exec_id into self_privunit_id Jann Horn
2016-09-18 18:13   ` Ben Hutchings
2016-09-18 18:31     ` Jann Horn
2016-09-18 18:45       ` Ben Hutchings
2016-09-18 19:08         ` Jann Horn [this message]
2016-09-18 19:57         ` Andy Lutomirski
2016-09-19 15:31           ` Jann Horn
2016-09-18 15:05 ` [PATCH 3/9] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-19 13:01   ` Stephen Smalley
2016-09-19 14:32     ` Jann Horn
2016-09-19 14:45       ` Stephen Smalley
2016-09-18 15:05 ` [PATCH 4/9] futex: don't leak robust_list pointer Jann Horn
2016-09-18 18:28   ` Ben Hutchings
2016-09-18 18:33     ` Jann Horn
2016-09-18 15:05 ` [PATCH 5/9] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-18 19:15   ` Jann Horn
2016-09-18 15:05 ` [PATCH 6/9] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-18 15:05 ` [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Jann Horn
2016-09-18 18:38   ` Ben Hutchings
2016-09-18 18:40     ` Jann Horn
2016-09-18 19:57   ` Andy Lutomirski
2016-09-18 20:38     ` Jann Horn
2016-09-18 20:18   ` Linus Torvalds
2016-09-18 20:52     ` Jann Horn
2016-09-18 15:05 ` [PATCH 8/9] fs/proc: fix attr access check Jann Horn
2016-09-18 15:05 ` [PATCH 9/9] Documentation: add security/ptrace_checks.txt Jann Horn

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