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Groups > linux.kernel > #1690075

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

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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 <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 kernel/sched/fair.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c95880e..5f7f997 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1130,7 +1130,7 @@ static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
 }
 
 struct numa_group {
-	atomic_t refcount;
+	refcount_t refcount;
 
 	spinlock_t lock; /* nr_tasks, tasks */
 	int nr_tasks;
@@ -2177,12 +2177,12 @@ 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);
 }
 
@@ -2203,7 +2203,7 @@ 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);
-- 
2.7.4

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[PATCH 00/15] v4 kernel core pieces refcount conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 03/15] sched: convert user_struct.__count to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 12/15] groups: convert group_info.usage to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 11/15] nsproxy: convert nsproxy.count to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 13/15] creds: convert cred.usage to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 10/15] uprobes: convert uprobe.ref to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 04/15] sched: convert numa_group.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 06/15] sched/task_struct: convert task_struct.stack_refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:40 +0200
  [PATCH 09/15] perf/ring_buffer: convert ring_buffer.aux_refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200
  [PATCH 07/15] perf: convert perf_event_context.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200
  [PATCH 08/15] perf/ring_buffer: convert ring_buffer.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200
  [PATCH 05/15] sched/task_struct: convert task_struct.usage to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200
  [PATCH 02/15] sched: convert signal_struct.sigcnt to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200
  [PATCH 01/15] sched: convert sighand_struct.count to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-18 12:50 +0200

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