[PATCH v2 5/6] sched: Use rq->rd in sched_setaffinity() under RCU read lock

[Kirill Tkhai <tkhai@yandex.ru>]

From: Kirill Tkhai <ktkhai@parallels.com>

task_rq(p)->rd and task_rq(p)->rd->span may be used-after-free here.
Probability of NULL pointer derefference isn't zero in this place.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Cc: <stable@vger.kernel.org> # v3.14+
---
 kernel/sched/core.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b07710..643ee99 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4023,13 +4023,14 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
 	 * root_domain.
 	 */
 #ifdef CONFIG_SMP
-	if (task_has_dl_policy(p)) {
-		const struct cpumask *span = task_rq(p)->rd->span;
-
-		if (dl_bandwidth_enabled() && !cpumask_subset(span, new_mask)) {
+	if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
+		rcu_read_lock();
+		if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
 			retval = -EBUSY;
+			rcu_read_unlock();
 			goto out_free_new_mask;
 		}
+		rcu_read_unlock();
 	}
 #endif
 again: