linux-kernel - [PATCH 04/15] drivers, net, mlx4: convert mlx4_qp.refcount from atomic_t to refcount

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Date:   Fri, 20 Oct 2017 10:23:38 +0300
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-hams@...r.kernel.org, linux-ppp@...r.kernel.org,
        ganeshgr@...lsio.com, nbd@...nwrt.org, john@...ozen.org,
        sean.wang@...iatek.com, matthias.bgg@...il.com,
        yishaih@...lanox.com, saeedm@...lanox.com, matanb@...lanox.com,
        tariqt@...lanox.com, leonro@...lanox.com,
        ajk@...nets.uni-bremen.de, paulus@...ba.org, zbr@...emap.net,
        peterz@...radead.org, keescook@...omium.org,
        Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH 04/15] drivers, net, mlx4: convert mlx4_qp.refcount from atomic_t to refcount_t

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 mlx4_qp.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@...omium.org>
Reviewed-by: David Windsor <dwindsor@...il.com>
Reviewed-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
---
 drivers/net/ethernet/mellanox/mlx4/qp.c | 8 ++++----
 include/linux/mlx4/device.h             | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/qp.c b/drivers/net/ethernet/mellanox/mlx4/qp.c
index 2033209..769598f 100644
--- a/drivers/net/ethernet/mellanox/mlx4/qp.c
+++ b/drivers/net/ethernet/mellanox/mlx4/qp.c
@@ -55,7 +55,7 @@ void mlx4_qp_event(struct mlx4_dev *dev, u32 qpn, int event_type)
 
 	qp = __mlx4_qp_lookup(dev, qpn);
 	if (qp)
-		atomic_inc(&qp->refcount);
+		refcount_inc(&qp->refcount);
 
 	spin_unlock(&qp_table->lock);
 
@@ -66,7 +66,7 @@ void mlx4_qp_event(struct mlx4_dev *dev, u32 qpn, int event_type)
 
 	qp->event(qp, event_type);
 
-	if (atomic_dec_and_test(&qp->refcount))
+	if (refcount_dec_and_test(&qp->refcount))
 		complete(&qp->free);
 }
 
@@ -420,7 +420,7 @@ int mlx4_qp_alloc(struct mlx4_dev *dev, int qpn, struct mlx4_qp *qp)
 	if (err)
 		goto err_icm;
 
-	atomic_set(&qp->refcount, 1);
+	refcount_set(&qp->refcount, 1);
 	init_completion(&qp->free);
 
 	return 0;
@@ -520,7 +520,7 @@ EXPORT_SYMBOL_GPL(mlx4_qp_remove);
 
 void mlx4_qp_free(struct mlx4_dev *dev, struct mlx4_qp *qp)
 {
-	if (atomic_dec_and_test(&qp->refcount))
+	if (refcount_dec_and_test(&qp->refcount))
 		complete(&qp->free);
 	wait_for_completion(&qp->free);
 
diff --git a/include/linux/mlx4/device.h b/include/linux/mlx4/device.h
index daac2e3..b8e19c4 100644
--- a/include/linux/mlx4/device.h
+++ b/include/linux/mlx4/device.h
@@ -768,7 +768,7 @@ struct mlx4_qp {
 
 	int			qpn;
 
-	atomic_t		refcount;
+	refcount_t		refcount;
 	struct completion	free;
 	u8			usage;
 };
-- 
2.7.4