netdev - Re: [PATCH] net: thunderbolt: Fix TCP/UDPv6 GSO checksum calculation

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Date: Mon, 11 Sep 2023 13:09:56 +0300
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Michael Jamet <michael.jamet@...el.com>,
	Yehezkel Bernat <YehezkelShB@...il.com>,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Alex Balcanquall <alex@...xbal.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: thunderbolt: Fix TCP/UDPv6 GSO checksum calculation

Hi,

On Mon, Sep 11, 2023 at 12:03:06PM +0200, Eric Dumazet wrote:
> On Mon, Sep 11, 2023 at 11:50 AM Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> >
> > Alex reported that running ssh over IPv6 does not work with
> > Thunderbolt/USB4 networking driver. The reason for that is that driver
> > should call skb_is_gso() before calling skb_is_gso_v6(), and it should
> > not return false after calculates the checksum successfully. This probably
> > was a copy paste error from the original driver where it was done
> > properly.
> >
> > While there add checksum calculation for UDPv6 GSO packets as well.
> 
> This part does not belong to this patch, and should be submitted for net-next.
> 
> Note that this driver is not supposed to receive UDP GSO packets.

Ah, indeed.

I took this part from the original driver that was submitted
around 2016-2017 timeframe but was never merged. This current driver is
reworked version but I missed the skb_is_gso() and the rest.

> >
> > Cc: stable@...r.kernel.org
> 
> What would be the Fixes: tag for this patch ?

It would be the initial commit:

Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")

But I was not sure if it is really practical here. I can add it to v2.

> > Reported-by: Alex Balcanquall <alex@...xbal.com>
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> >  drivers/net/thunderbolt/main.c | 21 +++++++++++++++------
> >  1 file changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/net/thunderbolt/main.c b/drivers/net/thunderbolt/main.c
> > index 0c1e8970ee58..ba50a554478f 100644
> > --- a/drivers/net/thunderbolt/main.c
> > +++ b/drivers/net/thunderbolt/main.c
> > @@ -1049,12 +1049,21 @@ static bool tbnet_xmit_csum_and_map(struct tbnet *net, struct sk_buff *skb,
> >                 *tucso = ~csum_tcpudp_magic(ip_hdr(skb)->saddr,
> >                                             ip_hdr(skb)->daddr, 0,
> >                                             ip_hdr(skb)->protocol, 0);
> > -       } else if (skb_is_gso_v6(skb)) {
> > -               tucso = dest + ((void *)&(tcp_hdr(skb)->check) - data);
> > -               *tucso = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
> > -                                         &ipv6_hdr(skb)->daddr, 0,
> > -                                         IPPROTO_TCP, 0);
> > -               return false;
> > +       } else if (skb_is_gso(skb)) {
> > +               if (skb_is_gso_v6(skb)) {
> > +                       tucso = dest + ((void *)&(tcp_hdr(skb)->check) - data);
> > +                       *tucso = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
> > +                                                 &ipv6_hdr(skb)->daddr, 0,
> > +                                                 IPPROTO_TCP, 0);
> > +               } else if (protocol == htons(ETH_P_IPV6) &&
> > +                          (skb_shinfo(skb)->gso_type & SKB_GSO_UDP)) {
> > +                       tucso = dest + ((void *)&(udp_hdr(skb)->check) - data);
> > +                       *tucso = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
> > +                                                 &ipv6_hdr(skb)->daddr, 0,
> > +                                                 IPPROTO_UDP, 0);
> 
> This is dead code in the current state of this driver.

Thanks! I will submit v2 with that dropped.

> > +               } else {
> > +                       return false;
> > +               }
> >         } else if (protocol == htons(ETH_P_IPV6)) {
> >                 tucso = dest + skb_checksum_start_offset(skb) + skb->csum_offset;
> >                 *tucso = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
> > --
> > 2.40.1
> >