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Date: Fri, 20 Oct 2017 16:08:47 +0800 From: Sean Wang <sean.wang@...iatek.com> To: Elena Reshetova <elena.reshetova@...el.com> CC: <davem@...emloft.net>, <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>, <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> Subject: Re: [PATCH 02/15] drivers, net, ethernet: convert mtk_eth.dma_refcnt from atomic_t to refcount_t On Fri, 2017-10-20 at 10:23 +0300, Elena Reshetova wrote: > 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(ð->dma_refcnt)) { > + if (!refcount_read(ð->dma_refcnt)) { > int err = mtk_start_dma(eth); > > if (err) > @@ -1827,8 +1827,10 @@ static int mtk_open(struct net_device *dev) > napi_enable(ð->rx_napi); > mtk_tx_irq_enable(eth, MTK_TX_DONE_INT); > mtk_rx_irq_enable(eth, MTK_RX_DONE_INT); > + refcount_set(ð->dma_refcnt, 1); the existing driver seems to have a missing initial atomic_set for the eth->dma_refcnt. > } > - atomic_inc(ð->dma_refcnt); > + else > + refcount_inc(ð->dma_refcnt); > how about add the initial refcount_set into probe handler, and keep logic else unchanged ? > 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(ð->dma_refcnt)) > + if (!refcount_dec_and_test(ð->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;
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