linux-kernel - [PATCH 5/7] fs, xfs: convert xlog_ticket.t_ref from atomic_t to refcount

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Date:   Tue, 21 Feb 2017 17:49:05 +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,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 5/7] fs, xfs: convert xlog_ticket.t_ref 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_log.c      | 10 +++++-----
 fs/xfs/xfs_log_priv.h |  4 +++-
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index b1469f0..c127fa0 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3500,8 +3500,8 @@ void
 xfs_log_ticket_put(
 	xlog_ticket_t	*ticket)
 {
-	ASSERT(atomic_read(&ticket->t_ref) > 0);
-	if (atomic_dec_and_test(&ticket->t_ref))
+	ASSERT(refcount_read(&ticket->t_ref) > 0);
+	if (refcount_dec_and_test(&ticket->t_ref))
 		kmem_zone_free(xfs_log_ticket_zone, ticket);
 }
 
@@ -3509,8 +3509,8 @@ xlog_ticket_t *
 xfs_log_ticket_get(
 	xlog_ticket_t	*ticket)
 {
-	ASSERT(atomic_read(&ticket->t_ref) > 0);
-	atomic_inc(&ticket->t_ref);
+	ASSERT(refcount_read(&ticket->t_ref) > 0);
+	refcount_inc(&ticket->t_ref);
 	return ticket;
 }
 
@@ -3632,7 +3632,7 @@ xlog_ticket_alloc(
 
 	unit_res = xfs_log_calc_unit_res(log->l_mp, unit_bytes);
 
-	atomic_set(&tic->t_ref, 1);
+	refcount_set(&tic->t_ref, 1);
 	tic->t_task		= current;
 	INIT_LIST_HEAD(&tic->t_queue);
 	tic->t_unit_res		= unit_res;
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index c2604a5..279afce 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -18,6 +18,8 @@
 #ifndef	__XFS_LOG_PRIV_H__
 #define __XFS_LOG_PRIV_H__
 
+#include <linux/refcount.h>
+
 struct xfs_buf;
 struct xlog;
 struct xlog_ticket;
@@ -168,7 +170,7 @@ typedef struct xlog_ticket {
 	struct list_head   t_queue;	 /* reserve/write queue */
 	struct task_struct *t_task;	 /* task that owns this ticket */
 	xlog_tid_t	   t_tid;	 /* transaction identifier	 : 4  */
-	atomic_t	   t_ref;	 /* ticket reference count       : 4  */
+	refcount_t	   t_ref;	 /* ticket reference count       : 4  */
 	int		   t_curr_res;	 /* current reservation in bytes : 4  */
 	int		   t_unit_res;	 /* unit reservation in bytes    : 4  */
 	char		   t_ocnt;	 /* original count		 : 1  */
-- 
2.7.4