linux-kernel - [PATCH 1/5] fs, xfs: convert xfs_bui_log_item.bui_refcount from atomic_t to refcount

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Date:   Wed,  1 Mar 2017 10:47:36 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-xfs@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, darrick.wong@...cle.com,
        david@...morbit.com, Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 1/5] fs, xfs: convert xfs_bui_log_item.bui_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>
---
 fs/xfs/xfs_bmap_item.c | 4 ++--
 fs/xfs/xfs_bmap_item.h | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
index 9bf57c7..33104ad 100644
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -199,7 +199,7 @@ xfs_bui_init(
 	buip->bui_format.bui_nextents = XFS_BUI_MAX_FAST_EXTENTS;
 	buip->bui_format.bui_id = (uintptr_t)(void *)buip;
 	atomic_set(&buip->bui_next_extent, 0);
-	atomic_set(&buip->bui_refcount, 2);
+	refcount_set(&buip->bui_refcount, 2);
 
 	return buip;
 }
@@ -215,7 +215,7 @@ void
 xfs_bui_release(
 	struct xfs_bui_log_item	*buip)
 {
-	if (atomic_dec_and_test(&buip->bui_refcount)) {
+	if (refcount_dec_and_test(&buip->bui_refcount)) {
 		xfs_trans_ail_remove(&buip->bui_item, SHUTDOWN_LOG_IO_ERROR);
 		xfs_bui_item_free(buip);
 	}
diff --git a/fs/xfs/xfs_bmap_item.h b/fs/xfs/xfs_bmap_item.h
index c867daa..988a6ae 100644
--- a/fs/xfs/xfs_bmap_item.h
+++ b/fs/xfs/xfs_bmap_item.h
@@ -20,6 +20,8 @@
 #ifndef	__XFS_BMAP_ITEM_H__
 #define	__XFS_BMAP_ITEM_H__
 
+#include <linux/refcount.h>
+
 /*
  * There are (currently) two pairs of bmap btree redo item types: map & unmap.
  * The common abbreviations for these are BUI (bmap update intent) and BUD
@@ -61,7 +63,7 @@ struct kmem_zone;
  */
 struct xfs_bui_log_item {
 	struct xfs_log_item		bui_item;
-	atomic_t			bui_refcount;
+	refcount_t			bui_refcount;
 	atomic_t			bui_next_extent;
 	unsigned long			bui_flags;	/* misc flags */
 	struct xfs_bui_log_format	bui_format;
-- 
2.7.4