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Date:   Mon, 20 Feb 2017 12:18:56 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     cgroups@...r.kernel.org, linux-audit@...hat.com,
        linux-fsdevel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, viro@...iv.linux.org.uk, tj@...nel.org,
        mingo@...hat.com, hannes@...xchg.org, lizefan@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        paul@...l-moore.com, eparis@...hat.com, akpm@...ux-foundation.org,
        arnd@...db.de, luto@...nel.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 07/19] kernel: convert ring_buffer.refcount from atomic_t to refcount_t

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.

Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.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 07a778b..e1c337d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5039,7 +5039,7 @@ 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();
@@ -5049,7 +5049,7 @@ 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 257fa46..8de1664 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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