On Fri, 2017-10-20 at 10:23 +0300, Elena Reshetova wrote:

quoted

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 <redacted>
Reviewed-by: David Windsor <redacted>
Reviewed-by: Hans Liljestrand <redacted>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.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

quoted

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

*/

quoted

-	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);

the existing driver seems to have a missing initial atomic_set for the
eth->dma_refcnt.

quoted

 	}
-	atomic_inc(&eth->dma_refcnt);
+	else
+		refcount_inc(&eth->dma_refcnt);

how about add the initial refcount_set into probe handler, and keep
logic else unchanged ?

Sure, I guess you mean mtk_probe() function? I can move the refcount_set to be there
and remove this change. 

Should I resend the modified patch to you (maybe then two of the ethernet patches)?

Best Regards,
Elena.

quoted

 	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

quoted

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];

quoted

 	struct mtk_rx_ring		rx_ring_qdma;

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