[04/15] sched: convert numa_group.refcount to refcount_t

Commit Message

Reshetova, Elena Aug. 30, 2017, 12:22 p.m. UTC

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable numa_group.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <[e-mail]>
Reviewed-by: David Windsor <[e-mail]>
Reviewed-by: Hans Liljestrand <[e-mail]>
Signed-off-by: Elena Reshetova <[e-mail]>
---
 kernel/sched/fair.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Patch

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a5d83ed..fe4e38c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1059,7 +1059,7 @@  unsigned int sysctl_numa_balancing_scan_size = 256;
 unsigned int sysctl_numa_balancing_scan_delay = 1000;
 
 struct numa_group {
-	atomic_t refcount;
+	refcount_t refcount;
 
 	spinlock_t lock; /* nr_tasks, tasks */
 	int nr_tasks;
@@ -1128,7 +1128,7 @@  static unsigned int task_scan_start(struct task_struct *p)
 		unsigned long shared = group_faults_shared(ng);
 		unsigned long private = group_faults_priv(ng);
 
-		period *= atomic_read(&ng->refcount);
+		period *= refcount_read(&ng->refcount);
 		period *= shared + 1;
 		period /= private + shared + 1;
 	}
@@ -1151,7 +1151,7 @@  static unsigned int task_scan_max(struct task_struct *p)
 		unsigned long private = group_faults_priv(ng);
 		unsigned long period = smax;
 
-		period *= atomic_read(&ng->refcount);
+		period *= refcount_read(&ng->refcount);
 		period *= shared + 1;
 		period /= private + shared + 1;
 
@@ -2236,12 +2236,12 @@  static void task_numa_placement(struct task_struct *p)
 
 static inline int get_numa_group(struct numa_group *grp)
 {
-	return atomic_inc_not_zero(&grp->refcount);
+	return refcount_inc_not_zero(&grp->refcount);
 }
 
 static inline void put_numa_group(struct numa_group *grp)
 {
-	if (atomic_dec_and_test(&grp->refcount))
+	if (refcount_dec_and_test(&grp->refcount))
 		kfree_rcu(grp, rcu);
 }
 
@@ -2262,7 +2262,7 @@  static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 		if (!grp)
 			return;
 
-		atomic_set(&grp->refcount, 1);
+		refcount_set(&grp->refcount, 1);
 		grp->active_nodes = 1;
 		grp->max_faults_cpu = 0;
 		spin_lock_init(&grp->lock);