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 ring_buffer.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
kernel/events/core.c | 4 ++--
kernel/events/internal.h | 3 ++-
kernel/events/ring_buffer.c | 2 +-
3 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7272b47..66d7e18 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5107,7 +5107,7 @@ struct ring_buffer *ring_buffer_get(struct perf_event *event)
rcu_read_lock();
rb = rcu_dereference(event->rb);
if (rb) {
- if (!atomic_inc_not_zero(&rb->refcount))
+ if (!refcount_inc_not_zero(&rb->refcount))
rb = NULL;
}
rcu_read_unlock();
@@ -5117,7 +5117,7 @@ struct ring_buffer *ring_buffer_get(struct perf_event *event)
void ring_buffer_put(struct ring_buffer *rb)
{
- if (!atomic_dec_and_test(&rb->refcount))
+ if (!refcount_dec_and_test(&rb->refcount))
return;
WARN_ON_ONCE(!list_empty(&rb->event_list));
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 843e970..1cdd9fa 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -3,13 +3,14 @@
#include <linux/hardirq.h>
#include <linux/uaccess.h>
+#include <linux/refcount.h>
/* Buffer handling */
#define RING_BUFFER_WRITABLE 0x01
struct ring_buffer {
- atomic_t refcount;
+ refcount_t refcount;
struct rcu_head rcu_head;
#ifdef CONFIG_PERF_USE_VMALLOC
struct work_struct work;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index f684d8e..86e1379 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -284,7 +284,7 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
else
rb->overwrite = 1;
- atomic_set(&rb->refcount, 1);
+ refcount_set(&rb->refcount, 1);
INIT_LIST_HEAD(&rb->event_list);
spin_lock_init(&rb->event_lock);
--
2.7.4
