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 b910072..1ae374b 100644 (file)
--- 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,