From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 23 Dec 2013 22:45:01 +0000 (-0500)
Subject: selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()
X-Git-Tag: v3.2.55~21
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5826e620694c056e27dae2f1e1e31005c93ab7e0;p=people%2Fms%2Flinux.git

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@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b910072eaaad..1ae374b2d126 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5374,11 +5374,11 @@ 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,