linux-kernel - Re: general protection fault in skb

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Message-ID: <CAF=yD-JLXo9T4XwnJZ6MqeQas5QM4qNTOic9jb3ZNHdeJPTfmA@mail.gmail.com>
Date:   Tue, 2 Jan 2018 18:23:27 +0100
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     syzbot <syzbot+fee64147a25aecd48055@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs@...glegroups.com,
        Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: general protection fault in skb_segment

> Actually, changes just to inet_gso_segment and ipv6_gso_segment
> will suffice:
>
>        bool udpfrag = false, fixedid = false, gso_partial, encap;
>         struct sk_buff *segs = ERR_PTR(-EINVAL);
> +       unsigned int offset = 0, gso_type;
>         const struct net_offload *ops;
> -       unsigned int offset = 0;
>         struct iphdr *iph;
>         int proto, tot_len;
>         int nhoff;
> @@ -1258,6 +1258,22 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
>
>         skb_reset_transport_header(skb);
>
> +       gso_type = skb_shinfo(skb)->gso_type;
> +       if (gso_type & SKB_GSO_DODGY) {
> +               switch (gso_type & (SKB_GSO_TCPV4 | SKB_GSO_UDP)) {
> +               case SKB_GSO_TCPV4:
> +                       if (proto != IPPROTO_TCP)
> +                               goto out;
> +                       break;
> +               case SKB_GSO_UDP:
> +                       if (proto != IPPROTO_UDP)
> +                               goto out;
> +                       break;
> +               default:
> +                       goto out;
> +               }
> +       }
>
> and analogous for IPv6. For a real patch I would deduplicate this
> logic between them and move it to a separate helper function
> (in a header file, then).

This approach would also need an skb->protocol check either in
virtio_net_hdr_to_skb or skb_mac_gso_segment.