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Date:   Thu, 16 Jan 2020 08:05:08 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     James Hughes <james.hughes@...pberrypi.org>
Cc:     netdev <netdev@...r.kernel.org>,
        RENARD Pierre-Francois <pfrenard@...il.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>
Subject: Re: [PATCH net] net: usb: lan78xx: limit size of local TSO packets

On Thu, Jan 16, 2020 at 6:26 AM James Hughes
<james.hughes@...pberrypi.org> wrote:
>
> Following on from Eric comment below, is this patch suitable for the
> forwarded packets case? I'm not familiar enough to be sure, and not
> aware of any way to test it. I've testing ethernet functionality on a
> Pi3B+ and see no regressions.
>
> Content of format patch of the commit, if it seems OK I'll submit a
> proper patch email.
>
> From b7f06bf6298904b106c38b4bac06a6fcebeee47e Mon Sep 17 00:00:00 2001
> From: James Hughes <james.hughes@...pberrypi.org>
> Date: Wed, 15 Jan 2020 13:41:54 +0000
> Subject: [PATCH] net: usb: lan78xx: Add .ndo_features_check
>
> As reported by Eric Dumazet, the driver does not handle skb's
> over a certain size in all possible cases. Most cases have been fixed,
> this patch should ensure that forwarded TSO packets that are greater than
> MAX_SINGLE_PACKET_SIZE - header size are software segmented and handled
> correctly.
>
> Signed-off-by: James Hughes <james.hughes@...pberrypi.org>
> ---
>  drivers/net/usb/lan78xx.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
> index bc572b921fe1..3c721dc1fc10 100644
> --- a/drivers/net/usb/lan78xx.c
> +++ b/drivers/net/usb/lan78xx.c
> @@ -31,6 +31,7 @@
>  #include <linux/mdio.h>
>  #include <linux/phy.h>
>  #include <net/ip6_checksum.h>
> +#include <net/vxlan.h>
>  #include <linux/interrupt.h>
>  #include <linux/irqdomain.h>
>  #include <linux/irq.h>
> @@ -3733,6 +3734,19 @@ static void lan78xx_tx_timeout(struct net_device *net)
>   tasklet_schedule(&dev->bh);
>  }
>
> +static netdev_features_t lan78xx_features_check(struct sk_buff *skb,
> + struct net_device *netdev,
> + netdev_features_t features)
> +{
> + if (skb_shinfo(skb)->gso_size > MAX_SINGLE_PACKET_SIZE - MAX_HEADER)
> + features &= ~NETIF_F_TSO;
>

Here gso_size is the payload size of each segment (typically around 1428 bytes)

What you need here is testing the whole packet length (no need to care
about MAX_HEADER btw)

Also prefer ~NETIF_F_GSO_MASK (otherwise IPv6 will still be broken)

if (skb->len > MAX_SINGLE_PACKET_SIZE)
    features &= ~NETIF_F_GSO_MASK;

 +
> + features = vlan_features_check(skb, features);
> + features = vxlan_features_check(skb, features);
> +
> + return features;
> +}
> +
>  static const struct net_device_ops lan78xx_netdev_ops = {
>   .ndo_open = lan78xx_open,
>   .ndo_stop = lan78xx_stop,
> @@ -3746,6 +3760,7 @@ static const struct net_device_ops lan78xx_netdev_ops = {
>   .ndo_set_features = lan78xx_set_features,
>   .ndo_vlan_rx_add_vid = lan78xx_vlan_rx_add_vid,
>   .ndo_vlan_rx_kill_vid = lan78xx_vlan_rx_kill_vid,
> + .ndo_features_check = lan78xx_features_check,
>  };
>
>  static void lan78xx_stat_monitor(struct timer_list *t)
> --
> 2.17.1
>
>
> On Mon, 13 Jan 2020 at 17:27, Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > lan78xx_tx_bh() makes sure to not exceed MAX_SINGLE_PACKET_SIZE
> > bytes in the aggregated packets it builds, but does
> > nothing to prevent large GSO packets being submitted.
> >
> > Pierre-Francois reported various hangs when/if TSO is enabled.
> >
> > For localy generated packets, we can use netif_set_gso_max_size()
> > to limit the size of TSO packets.
> >
> > Note that forwarded packets could still hit the issue,
> > so a complete fix might require implementing .ndo_features_check
> > for this driver, forcing a software segmentation if the size
> > of the TSO packet exceeds MAX_SINGLE_PACKET_SIZE.
> >
> > Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Reported-by: RENARD Pierre-Francois <pfrenard@...il.com>
> > Tested-by: RENARD Pierre-Francois <pfrenard@...il.com>
> > Cc: Stefan Wahren <stefan.wahren@...e.com>
> > Cc: Woojung Huh <woojung.huh@...rochip.com>
> > Cc: Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>
> > ---
> >  drivers/net/usb/lan78xx.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
> > index fb4781080d6dec2af22f41c5e064350ea74130b3..75bdfae5f3e20afef3d2880171c7c6e8511546c5 100644
> > --- a/drivers/net/usb/lan78xx.c
> > +++ b/drivers/net/usb/lan78xx.c
> > @@ -3750,6 +3750,7 @@ static int lan78xx_probe(struct usb_interface *intf,
> >
> >         /* MTU range: 68 - 9000 */
> >         netdev->max_mtu = MAX_SINGLE_PACKET_SIZE;
> > +       netif_set_gso_max_size(netdev, MAX_SINGLE_PACKET_SIZE - MAX_HEADER);
> >
> >         dev->ep_blkin = (intf->cur_altsetting)->endpoint + 0;
> >         dev->ep_blkout = (intf->cur_altsetting)->endpoint + 1;
> > --
> > 2.25.0.rc1.283.g88dfdc4193-goog
> >
>
>
> --
> James Hughes
> Principal Software Engineer,
> Raspberry Pi (Trading) Ltd

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