netdev - [PATCH 02/15] drivers, net, ethernet: convert mtk_eth.dma_refcnt from atomic_t to refcount

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Date:   Fri, 20 Oct 2017 10:23:36 +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 02/15] drivers, net, ethernet: convert mtk_eth.dma_refcnt 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 mtk_eth.dma_refcnt 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/mediatek/mtk_eth_soc.c | 8 +++++---
 drivers/net/ethernet/mediatek/mtk_eth_soc.h | 4 +++-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 5e81a72..54adfd9 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -1817,7 +1817,7 @@ static int mtk_open(struct net_device *dev)
 	struct mtk_eth *eth = mac->hw;
 
 	/* we run 2 netdevs on the same dma ring so we only bring it up once */
-	if (!atomic_read(&eth->dma_refcnt)) {
+	if (!refcount_read(&eth->dma_refcnt)) {
 		int err = mtk_start_dma(eth);
 
 		if (err)
@@ -1827,8 +1827,10 @@ static int mtk_open(struct net_device *dev)
 		napi_enable(&eth->rx_napi);
 		mtk_tx_irq_enable(eth, MTK_TX_DONE_INT);
 		mtk_rx_irq_enable(eth, MTK_RX_DONE_INT);
+		refcount_set(&eth->dma_refcnt, 1);
 	}
-	atomic_inc(&eth->dma_refcnt);
+	else
+		refcount_inc(&eth->dma_refcnt);
 
 	phy_start(dev->phydev);
 	netif_start_queue(dev);
@@ -1868,7 +1870,7 @@ static int mtk_stop(struct net_device *dev)
 	phy_stop(dev->phydev);
 
 	/* only shutdown DMA if this is the last user */
-	if (!atomic_dec_and_test(&eth->dma_refcnt))
+	if (!refcount_dec_and_test(&eth->dma_refcnt))
 		return 0;
 
 	mtk_tx_irq_disable(eth, MTK_TX_DONE_INT);
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 3d3c24a..a3af466 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -15,6 +15,8 @@
 #ifndef MTK_ETH_H
 #define MTK_ETH_H
 
+#include <linux/refcount.h>
+
 #define MTK_QDMA_PAGE_SIZE	2048
 #define	MTK_MAX_RX_LENGTH	1536
 #define MTK_TX_DMA_BUF_LEN	0x3fff
@@ -632,7 +634,7 @@ struct mtk_eth {
 	struct regmap			*pctl;
 	u32				chip_id;
 	bool				hwlro;
-	atomic_t			dma_refcnt;
+	refcount_t			dma_refcnt;
 	struct mtk_tx_ring		tx_ring;
 	struct mtk_rx_ring		rx_ring[MTK_MAX_RX_RING_NUM];
 	struct mtk_rx_ring		rx_ring_qdma;
-- 
2.7.4