[PATCH 3.4 10/43] selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()

From: Greg Kroah-Hartman
Date: Mon Jan 06 2014 - 17:56:02 EST

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


From: Oleg Nesterov <oleg@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Paul Moore <pmoore@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

security/selinux/hooks.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5445,11 +5445,11 @@ 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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