Re: [PATCH net v1] lan743x: fix ethernet frame cutoff issue

[George McCollister]

On Thu, Apr 8, 2021 at 7:39 PM Sven Van Asbroeck <thesven73@xxxxxxxxx> wrote:
>
> From: Sven Van Asbroeck <thesven73@xxxxxxxxx>
>
> The ethernet frame length is calculated incorrectly. Depending on
> the value of RX_HEAD_PADDING, this may result in ethernet frames
> that are too short (cut off at the end), or too long (garbage added
> to the end).
>
> Fix by calculating the ethernet frame length correctly. For added
> clarity, use the ETH_FCS_LEN constant in the calculation.
>
> Many thanks to Heiner Kallweit for suggesting this solution.
>
> Fixes: 3e21a10fdea3 ("lan743x: trim all 4 bytes of the FCS; not just 2")
> Link: https://lore.kernel.org/lkml/20210408172353.21143-1-TheSven73@xxxxxxxxx/
> Signed-off-by: Sven Van Asbroeck <thesven73@xxxxxxxxx>

I'm glad everyone was able to work together to get this fixed properly
without any figure pointing or mud slinging! Kudos everyone.

Reviewed-by: George McCollister <george.mccollister@xxxxxxxxx>
Tested-By: George McCollister <george.mccollister@xxxxxxxxx>

> ---
>
> Tree: git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git # 864db232dc70
>
> To: Bryan Whitehead <bryan.whitehead@xxxxxxxxxxxxx>
> To: "David S. Miller" <davem@xxxxxxxxxxxxx>
> To: Jakub Kicinski <kuba@xxxxxxxxxx>
> To: George McCollister <george.mccollister@xxxxxxxxx>
> Cc: Heiner Kallweit <hkallweit1@xxxxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>
> Cc: UNGLinuxDriver@xxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
>
>  drivers/net/ethernet/microchip/lan743x_main.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
> index 1c3e204d727c..7b6794aa8ea9 100644
> --- a/drivers/net/ethernet/microchip/lan743x_main.c
> +++ b/drivers/net/ethernet/microchip/lan743x_main.c
> @@ -885,8 +885,8 @@ static int lan743x_mac_set_mtu(struct lan743x_adapter *adapter, int new_mtu)
>         }
>
>         mac_rx &= ~(MAC_RX_MAX_SIZE_MASK_);
> -       mac_rx |= (((new_mtu + ETH_HLEN + 4) << MAC_RX_MAX_SIZE_SHIFT_) &
> -                 MAC_RX_MAX_SIZE_MASK_);
> +       mac_rx |= (((new_mtu + ETH_HLEN + ETH_FCS_LEN)
> +                 << MAC_RX_MAX_SIZE_SHIFT_) & MAC_RX_MAX_SIZE_MASK_);
>         lan743x_csr_write(adapter, MAC_RX, mac_rx);
>
>         if (enabled) {
> @@ -1944,7 +1944,7 @@ static int lan743x_rx_init_ring_element(struct lan743x_rx *rx, int index)
>         struct sk_buff *skb;
>         dma_addr_t dma_ptr;
>
> -       buffer_length = netdev->mtu + ETH_HLEN + 4 + RX_HEAD_PADDING;
> +       buffer_length = netdev->mtu + ETH_HLEN + ETH_FCS_LEN + RX_HEAD_PADDING;
>
>         descriptor = &rx->ring_cpu_ptr[index];
>         buffer_info = &rx->buffer_info[index];
> @@ -2040,7 +2040,7 @@ lan743x_rx_trim_skb(struct sk_buff *skb, int frame_length)
>                 dev_kfree_skb_irq(skb);
>                 return NULL;
>         }
> -       frame_length = max_t(int, 0, frame_length - RX_HEAD_PADDING - 4);
> +       frame_length = max_t(int, 0, frame_length - ETH_FCS_LEN);
>         if (skb->len > frame_length) {
>                 skb->tail -= skb->len - frame_length;
>                 skb->len = frame_length;
> --
> 2.17.1
>