netdev - Re: [PATCH net] gso: validate gso_type if SKB_GSO

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Date:   Thu, 18 Jan 2018 11:48:54 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, edumazet@...gle.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] gso: validate gso_type if SKB_GSO_DODGY



On 2018年01月18日 07:11, Willem de Bruijn wrote:
> From: Willem de Bruijn<willemb@...gle.com>
>
> Validate gso_type of untrusted SKB_GSO_DODGY packets during
> segmentation.
>
> Untrusted user packets are limited to a small set of gso types in
> virtio_net_hdr_to_skb. But segmentation occurs on packet contents.
> Syzkaller was able to enter gso callbacks that are not hardened
> against untrusted user input.
>
> Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")

This commit is suspicious, I guess it should be 5c7cdf339af5 ("gso: 
Remove arbitrary checks for unsupported GSO")

> Link:http://lkml.kernel.org/r/<001a1137452496ffc305617e5fe0@...gle.com>
> Reported-by:syzbot+fee64147a25aecd48055@...kaller.appspotmail.com
> Signed-off-by: Willem de Bruijn<willemb@...gle.com>
> ---
>   net/ipv4/af_inet.c     | 21 +++++++++++++++++++++
>   net/ipv6/ip6_offload.c | 23 ++++++++++++++++++++++-
>   2 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index f00499a46927..d5a36827f7b1 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1220,6 +1220,25 @@ int inet_sk_rebuild_header(struct sock *sk)
>   }
>   EXPORT_SYMBOL(inet_sk_rebuild_header);
>   
> +static bool inet_gso_validate_dodgy(struct sk_buff *skb, int ipproto)
> +{
> +	unsigned int gso_type = skb_shinfo(skb)->gso_type;
> +
> +	if (gso_type & SKB_GSO_DODGY) {
> +		switch (gso_type & ~SKB_GSO_DODGY) {
> +		case SKB_GSO_TCPV4:
> +		case SKB_GSO_TCPV4 | SKB_GSO_TCP_ECN:
> +			return ipproto == IPPROTO_TCP;
> +		case SKB_GSO_UDP:
> +			return ipproto == IPPROTO_UDP;
> +		default:
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}

This seems more strict than what was removed by 5c7cdf339af5. Any reason 
for this? I'm asking since this probably work for virito-net but I'm not 
sure it works for other sources.

Thanks