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SubjectRe: [PATCH 02/15] drivers, net, ethernet: convert mtk_eth.dma_refcnt from atomic_t to refcount_t
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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@chromium.org>
> Reviewed-by: David Windsor <dwindsor@gmail.com>
> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
> 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
> 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);

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

> }
> - 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 ?

> 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;


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