linux-kernel - [PATCH v2] selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read

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Message-ID: <20131214163317.GB21675@redhat.com>
Date:	Sat, 14 Dec 2013 17:33:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Paul Moore <paul@...l-moore.com>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <james.l.morris@...cle.com>,
	Eric Paris <eparis@...isplace.org>,
	Evan McNabb <emcnabb@...hat.com>,
	Jan Stancek <jstancek@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2] selinux: selinux_setprocattr()->ptrace_parent() needs
	rcu_read_lock()

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@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 security/selinux/hooks.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5503,11 +5503,11 @@ static int selinux_setprocattr(struct ta
 		/* 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,

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