netdev - Re: [PATCH net v3] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may

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Message-ID: <CANn89iJOz_PQ_N4e=FS+toEDfLw-Ei9SwV6LU9Jmsvhtyxb7SQ@mail.gmail.com>
Date: Mon, 19 Jan 2026 18:17:45 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Florian Westphal <fw@...len.de>, netdev@...r.kernel.org, pabeni@...hat.com, 
	syzbot+6023ea32e206eef7920a@...kaller.appspotmail.com, davem@...emloft.net, 
	Mazin Al Haddad <mazin@...state.dev>
Subject: Re: [PATCH net v3] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may_pull()

On Mon, Jan 19, 2026 at 6:06 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 19 Jan 2026 12:24:57 +0100 Florian Westphal wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > I added skb_vlan_inet_prepare() helper in the cited commit, hinting
> > that we would need to use it more broadly.
>
> I _think_ this makes GRE forwarding tests a bit unhappy:
>
> https://netdev.bots.linux.dev/contest.html?branch=net-next-2026-01-19--12-00&executor=vmksft-forwarding&pw-n=0&pass=0
> --

I was unsure about ip6erspan_tunnel_xmit() change, I think I started
full tests days ago but probably was distracted.

I had :

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index d19d86ed43766bbc8ec052113be02ab231a5272c..9e214c355e6ce15fa828866ae20fa8fe321b4bf7
100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -881,7 +881,7 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff *skb,
        __be16 payload_protocol;
        int ret;

-       if (!pskb_inet_may_pull(skb))
+       if (skb_vlan_inet_prepare(skb, true))
                goto tx_err;

        if (!ip6_tnl_xmit_ctl(t, &t->parms.laddr, &t->parms.raddr))
@@ -929,7 +929,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct
sk_buff *skb,
        __u32 mtu;
        int nhoff;

-       if (!pskb_inet_may_pull(skb))
+       if (skb_vlan_inet_prepare(skb, false))
                goto tx_err;

        if (!ip6_tnl_xmit_ctl(t, &t->parms.laddr, &t->parms.raddr))