linux-kernel - Re: CVE-2022-48936: gso: do not skip outer ip header in case of ipip and net

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Message-ID: <z3hh3yrf5wym3obgol6obh3dkmqoc3rwbkj23qcmadf63b47h2@nn2232wngans>
Date: Tue, 27 Aug 2024 17:02:36 +0200
From: Michal Koutný <mkoutny@...e.com>
To: cve@...nel.org, linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Tao Liu <thomas.liu@...oud.cn>, Willem de Bruijn <willemb@...gle.com>
Subject: Re: CVE-2022-48936: gso: do not skip outer ip header in case of ipip
 and net_failover

On Thu, Aug 22, 2024 at 11:31:37AM GMT, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> We encounter a tcp drop issue in our cloud environment. Packet GROed in
> host forwards to a VM virtio_net nic with net_failover enabled. VM acts
> as a IPVS LB with ipip encapsulation. The full path like:
> host gro -> vm virtio_net rx -> net_failover rx -> ipvs fullnat
>  -> ipip encap -> net_failover tx -> virtio_net tx
> 
> When net_failover transmits a ipip pkt (gso_type = 0x0103, which means
> SKB_GSO_TCPV4, SKB_GSO_DODGY and SKB_GSO_IPXIP4), there is no gso
> did because it supports TSO and GSO_IPXIP4. But network_header points to
> inner ip header.
> 
> Call Trace:
>  tcp4_gso_segment        ------> return NULL
>  inet_gso_segment        ------> inner iph, network_header points to
>  ipip_gso_segment
>  inet_gso_segment        ------> outer iph
>  skb_mac_gso_segment

> Afterwards virtio_net transmits the pkt, only inner ip header is modified.
> And the outer one just keeps unchanged. The pkt will be dropped in remote
> host.

That may appear like a transient connection issue or permanently
impossible connection?

> Call Trace:
>  inet_gso_segment        ------> inner iph, outer iph is skipped
>  skb_mac_gso_segment
>  __skb_gso_segment
>  validate_xmit_skb
>  validate_xmit_skb_list
>  sch_direct_xmit
>  __qdisc_run
>  __dev_queue_xmit        ------> virtio_net
>  dev_hard_start_xmit
>  __dev_queue_xmit        ------> net_failover
>  ip_finish_output2
>  ip_output
>  iptunnel_xmit
>  ip_tunnel_xmit
>  ipip_tunnel_xmit        ------> ipip
>  dev_hard_start_xmit
>  __dev_queue_xmit
>  ip_finish_output2
>  ip_output
>  ip_forward
>  ip_rcv
>  __netif_receive_skb_one_core
>  netif_receive_skb_internal
>  napi_gro_receive
>  receive_buf
>  virtnet_poll
>  net_rx_action
> 
> The root cause of this issue is specific with the rare combination of
> SKB_GSO_DODGY and a tunnel device that adds an SKB_GSO_ tunnel option.
> SKB_GSO_DODGY is set from external virtio_net. We need to reset network
> header when callbacks.gso_segment() returns NULL.

Who's in control of these configuration (who can cause this incorrect
packet being sent)?

> This patch also includes ipv6_gso_segment(), considering SIT, etc.
> 
> The Linux kernel CVE team has assigned CVE-2022-48936 to this issue.

What is the security issue here?

Thanks,
Michal

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