From: Ingo Molnar <mingo@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Serge Hallyn <serge.hallyn@canonical.com>,
linux-kernel@vger.kernel.org,
Darren Hart <dvhart@linux.intel.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andrew Morton <akpm@linux-foundation.org>,
Jiri Kosina <jkosina@suse.cz>,
"Eric W. Biederman" <ebiederm@xmission.com>,
David Howells <dhowells@redhat.com>,
kernel-hardening@lists.openwall.com, spender@grsecurity.net
Subject: Re: [PATCH] futex: do not leak robust list to unprivileged process
Date: Tue, 20 Mar 2012 18:23:01 +0100 [thread overview]
Message-ID: <20120320172300.GA8888@gmail.com> (raw)
In-Reply-To: <CAGXu5jKVx41+NSEWsw0YF74z5_heSQ6GOmkuDi1DXNPcO4sjTQ@mail.gmail.com>
* Kees Cook <keescook@chromium.org> wrote:
> On Tue, Mar 20, 2012 at 10:02 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Tue, 20 Mar 2012, Serge Hallyn wrote:
> >
> >> Quoting Kees Cook (keescook@chromium.org):
> >> > It was possible to extract the robust list head address from a setuid
> >> > process if it had used set_robust_list(), allowing an ASLR info leak. This
> >> > changes the permission checks to be the same as those used for similar
> >> > info that comes out of /proc.
> >> >
> >> > Running a setuid program that uses robust futexes would have had:
> >> > cred->euid != pcred->euid
> >> > cred->euid == pcred->uid
> >> > so the old permissions check would allow it. I'm not aware of any setuid
> >> > programs that use robust futexes, so this is just a preventative measure.
> >> >
> >> > (This patch is based on changes from grsecurity.)
> >> >
> >> > Signed-off-by: Kees Cook <keescook@chromium.org>
> >>
> >> I like the change. Much cleaner. I'm not 100% sure though that
> >> there are no legitimate cases of robust futexes use which would now
> >> be forbidden. (Explicitly cc:ing Ingo)
> >
> > get_robust_list is not necessary for robust futexes. There is no
> > reference to get_robust_list in glibc.
> >
> > I really wonder why we have this syscall at all.
>
> The documentation I found yesterday while looking at this was:
> http://linux.die.net/man/2/get_robust_list
>
> Which says "The system call is only available for debugging
> purposes and is not needed for normal operations. Both system
> calls are not available to application programs as functions;
> they can be called using the syscall(3) function."
>
> Dropping the syscall entirely would certainly make it secure.
> ;)
The thinking was API completeness. In general it's possible for
a sufficiently privileged task to figure out all the state of a
task. We can query timers, fds - the robust list is such a
resource as well. The information leakage was obviously not
intended.
Thanks,
Ingo
next prev parent reply other threads:[~2012-03-20 17:23 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-19 23:12 [PATCH] futex: do not leak robust list to unprivileged process Kees Cook
2012-03-20 13:31 ` Serge Hallyn
2012-03-20 17:02 ` Thomas Gleixner
2012-03-20 17:11 ` Kees Cook
2012-03-20 17:23 ` Ingo Molnar [this message]
2012-03-22 23:46 ` Thomas Gleixner
2012-03-23 17:58 ` [PATCH] futex: mark get_robust_list as deprecated Kees Cook
2012-03-23 18:27 ` Thomas Gleixner
2012-03-23 19:08 ` Kees Cook
2012-03-23 19:08 ` [PATCH v2] " Kees Cook
2012-03-23 22:06 ` Eric W. Biederman
2012-03-23 22:10 ` Kees Cook
2012-03-30 5:05 ` Matt Helsley
2012-03-30 6:14 ` Pavel Emelyanov
2012-03-30 22:51 ` Gene Cooperman
2012-03-27 18:05 ` Josh Boyer
2012-03-27 19:13 ` Peter Zijlstra
2012-03-29 9:56 ` [tip:core/locking] futex: Mark " tip-bot for Kees Cook
2012-08-02 10:35 ` [PATCH v2] futex: mark " richard -rw- weinberger
2012-08-02 11:11 ` Eric W. Biederman
2012-08-03 10:17 ` richard -rw- weinberger
2012-08-03 11:02 ` Cyrill Gorcunov
2012-08-03 11:19 ` richard -rw- weinberger
2012-08-03 11:27 ` Cyrill Gorcunov
2012-08-03 11:30 ` richard -rw- weinberger
2012-08-03 11:35 ` Cyrill Gorcunov
2012-08-03 11:38 ` richard -rw- weinberger
2012-08-03 12:38 ` Pavel Emelyanov
2012-08-03 12:58 ` Eric W. Biederman
2012-08-03 13:00 ` richard -rw- weinberger
2012-08-03 17:16 ` Kees Cook
2012-03-28 18:33 ` [PATCH] futex: do not leak robust list to unprivileged process Kees Cook
2012-03-28 21:24 ` Thomas Gleixner
2012-03-29 9:55 ` [tip:core/locking] futex: Do " tip-bot for Kees Cook
2012-06-19 1:41 ` Wanlong Gao
2012-06-19 2:24 ` Serge Hallyn
2012-06-19 2:32 ` Wanlong Gao
2012-06-19 3:13 ` Serge Hallyn
2012-06-19 3:21 ` Wanlong Gao
2012-06-19 12:23 ` Serge Hallyn
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