releases/3.10.42/futex-prevent-attaching-to-kernel-threads.patch

From f0d71b3dcb8332f7971b5f2363632573e6d9486a Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 12 May 2014 20:45:35 +0000
Subject: futex: Prevent attaching to kernel threads

From: Thomas Gleixner <tglx@linutronix.de>

commit f0d71b3dcb8332f7971b5f2363632573e6d9486a upstream.

We happily allow userspace to declare a random kernel thread to be the
owner of a user space PI futex.

Found while analysing the fallout of Dave Jones syscall fuzzer.

We also should validate the thread group for private futexes and find
some fast way to validate whether the "alleged" owner has RW access on
the file which backs the SHM, but that's a separate issue.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Jones <davej@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <darren@dvhart.com>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Roland McGrath <roland@hack.frob.com>
Cc: Carlos ODonell <carlos@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: http://lkml.kernel.org/r/20140512201701.194824402@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/futex.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -666,6 +666,11 @@ lookup_pi_state(u32 uval, struct futex_h
 	if (!p)
 		return -ESRCH;
 
+	if (!p->mm) {
+		put_task_struct(p);
+		return -EPERM;
+	}
+
 	/*
 	 * We need to look at the task state flags to figure out,
 	 * whether the task is exiting. To protect against the do_exit