linux-kernel - Re: [EXT] [PATCH net v2] ipv4: ip_gre: Avoid skb_pull() failure in ipgre

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Message-ID: <CANn89iLaCrBGdtVSPZMLM7tnixFfy3wF98aojxkcoXoXEit6og@mail.gmail.com>
Date:   Sun, 3 Dec 2023 12:03:07 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Suman Ghosh <sumang@...vell.com>
Cc:     Shigeru Yoshida <syoshida@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] [PATCH net v2] ipv4: ip_gre: Avoid skb_pull() failure in ipgre_xmit()

On Sun, Dec 3, 2023 at 7:58 AM Suman Ghosh <sumang@...vell.com> wrote:
>
> Hi Shigeru,
>
> >diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index
> >22a26d1d29a0..5169c3c72cff 100644
> >--- a/net/ipv4/ip_gre.c
> >+++ b/net/ipv4/ip_gre.c
> >@@ -635,15 +635,18 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
> >       }
> >
> >       if (dev->header_ops) {
> >+              int pull_len = tunnel->hlen + sizeof(struct iphdr);
> >+
> >               if (skb_cow_head(skb, 0))
> >                       goto free_skb;
> >
> >               tnl_params = (const struct iphdr *)skb->data;
> >
> >-              /* Pull skb since ip_tunnel_xmit() needs skb->data pointing
> >-               * to gre header.
> >-               */
> >-              skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
> >+              if (!pskb_network_may_pull(skb, pull_len))
> [Suman] Since this is transmit path, should we add unlikely() here?

Adding unlikely() is not needed, it is already done generically from
the inline helpers.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>