[3.5.y.z extended stable] Patch "selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c5ccce5f7638f732ae7bcb2cd352eb4902dcabc7 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg at redhat.com>
Date: Mon, 23 Dec 2013 17:45:01 -0500
Subject: selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()

commit c0c1439541f5305b57a83d599af32b74182933fe upstream.

selinux_setprocattr() does ptrace_parent(p) under task_lock(p),
but task_struct->alloc_lock doesn't pin ->parent or ->ptrace,
this looks confusing and triggers the "suspicious RCU usage"
warning because ptrace_parent() does rcu_dereference_check().

And in theory this is wrong, spin_lock()->preempt_disable()
doesn't necessarily imply rcu_read_lock() we need to access
the ->parent.

Reported-by: Evan McNabb <emcnabb at redhat.com>
Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Signed-off-by: Paul Moore <pmoore at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 security/selinux/hooks.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 092d322..edc54e5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5465,11 +5465,11 @@ static int selinux_setprocattr(struct task_struct *p,
 		/* Check for ptracing, and update the task SID if ok.
 		   Otherwise, leave SID unchanged and fail. */
 		ptsid = 0;
-		task_lock(p);
+		rcu_read_lock();
 		tracer = ptrace_parent(p);
 		if (tracer)
 			ptsid = task_sid(tracer);
-		task_unlock(p);
+		rcu_read_unlock();

 		if (tracer) {
 			error = avc_has_perm(ptsid, sid, SECCLASS_PROCESS,
--
1.8.3.2