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SubjectRE: [PATCH 03/14] net: axienet: Fix DMA descriptor cleanup path
Date
> -----Original Message-----
> From: Andre Przywara <andre.przywara@arm.com>
> Sent: Friday, January 10, 2020 5:24 PM
> To: David S . Miller <davem@davemloft.net>; Radhey Shyam Pandey
> <radheys@xilinx.com>
> Cc: Michal Simek <michals@xilinx.com>; Robert Hancock
> <hancock@sedsystems.ca>; netdev@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: [PATCH 03/14] net: axienet: Fix DMA descriptor cleanup path
>
> When axienet_dma_bd_init() bails out during the initialisation process,
> it might do so with parts of the structure already allocated and
> initialised, while other parts have not been touched yet. Before
> returning in this case, we call axienet_dma_bd_release(), which does not
> take care of this corner case.
> This is most obvious by the first loop happily dereferencing
> lp->rx_bd_v, which we actually check to be non NULL *afterwards*.
>
> Make sure we only unmap or free already allocated structures, by:
> - directly returning with -ENOMEM if nothing has been allocated at all
> - checking for lp->rx_bd_v to be non-NULL *before* using it
> - only unmapping allocated DMA RX regions
>
> This avoids NULL pointer dereferences when initialisation fails.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> .../net/ethernet/xilinx/xilinx_axienet_main.c | 43 ++++++++++++-------
> 1 file changed, 28 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 97482cf093ce..7e90044cf2d9 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -160,24 +160,37 @@ static void axienet_dma_bd_release(struct
> net_device *ndev)
> int i;
> struct axienet_local *lp = netdev_priv(ndev);
>
> + /* If we end up here, tx_bd_v must have been DMA allocated. */
> + dma_free_coherent(ndev->dev.parent,
> + sizeof(*lp->tx_bd_v) * lp->tx_bd_num,
> + lp->tx_bd_v,
> + lp->tx_bd_p);
> +
> + if (!lp->rx_bd_v)
> + return;
> +
> for (i = 0; i < lp->rx_bd_num; i++) {
> - dma_unmap_single(ndev->dev.parent, lp->rx_bd_v[i].phys,
> - lp->max_frm_size, DMA_FROM_DEVICE);
> + /* A NULL skb means this descriptor has not been initialised
> + * at all.
> + */
> + if (!lp->rx_bd_v[i].skb)
> + break;
> +
> dev_kfree_skb(lp->rx_bd_v[i].skb);
> - }
>
> - if (lp->rx_bd_v) {
> - dma_free_coherent(ndev->dev.parent,
> - sizeof(*lp->rx_bd_v) * lp->rx_bd_num,
> - lp->rx_bd_v,
> - lp->rx_bd_p);
> - }
> - if (lp->tx_bd_v) {
> - dma_free_coherent(ndev->dev.parent,
> - sizeof(*lp->tx_bd_v) * lp->tx_bd_num,
> - lp->tx_bd_v,
> - lp->tx_bd_p);
> + /* For each descriptor, we programmed cntrl with the (non-
> zero)
> + * descriptor size, after it had been successfully allocated.
> + * So a non-zero value in there means we need to unmap it.
> + */

> + if (lp->rx_bd_v[i].cntrl)

I think it should ok to unmap w/o any check?
> + dma_unmap_single(ndev->dev.parent, lp-
> >rx_bd_v[i].phys,
> + lp->max_frm_size,
> DMA_FROM_DEVICE);
> }
> +
> + dma_free_coherent(ndev->dev.parent,
> + sizeof(*lp->rx_bd_v) * lp->rx_bd_num,
> + lp->rx_bd_v,
> + lp->rx_bd_p);
> }
>
> /**
> @@ -207,7 +220,7 @@ static int axienet_dma_bd_init(struct net_device
> *ndev)
> sizeof(*lp->tx_bd_v) * lp-
> >tx_bd_num,
> &lp->tx_bd_p, GFP_KERNEL);
> if (!lp->tx_bd_v)
> - goto out;
> + return -ENOMEM;
>
> lp->rx_bd_v = dma_alloc_coherent(ndev->dev.parent,
> sizeof(*lp->rx_bd_v) * lp-
> >rx_bd_num,
> --
> 2.17.1

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