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Subject[PATCH 07/15] kernel: convert ring_buffer.refcount from atomic_t to refcount_t
Date
refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

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/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 faf9925..9147397 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5049,7 +5049,7 @@ 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();
@@ -5059,7 +5059,7 @@ 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 486fd78..b8e6fdf 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 ee97196..3353572 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
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