[PATCH 3.11 28/93] futex: Prevent attaching to kernel threads

[Luis Henriques]

3.11.10.12 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx at 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 at linutronix.de>
Cc: Dave Jones <davej at redhat.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Darren Hart <darren at dvhart.com>
Cc: Davidlohr Bueso <davidlohr at hp.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Clark Williams <williams at redhat.com>
Cc: Paul McKenney <paulmck at linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs at cn.fujitsu.com>
Cc: Roland McGrath <roland at hack.frob.com>
Cc: Carlos ODonell <carlos at redhat.com>
Cc: Jakub Jelinek <jakub at redhat.com>
Cc: Michael Kerrisk <mtk.manpages at gmail.com>
Cc: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
Link: http://lkml.kernel.org/r/20140512201701.194824402@linutronix.de
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/futex.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 3e876641f4af..a62447d335ab 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -667,6 +667,11 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 	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
-- 
1.9.1