On Mon, Mar 08, 2021 at 11:31:25AM +0100, Balazs Nemeth wrote:
> For gso packets, virtio_net_hdr_set_proto sets the protocol (if it isn't
> set) based on the type in the virtio net hdr, but the skb could contain
> anything since it could come from packet_snd through a raw socket. If
> there is a mismatch between what virtio_net_hdr_set_proto sets and
> the actual protocol, then the skb could be handled incorrectly later
> on.
>
> An example where this poses an issue is with the subsequent call to
> skb_flow_dissect_flow_keys_basic which relies on skb->protocol being set
> correctly. A specially crafted packet could fool
> skb_flow_dissect_flow_keys_basic preventing EINVAL to be returned.
>
> Avoid blindly trusting the information provided by the virtio net header
> by checking that the protocol in the packet actually matches the
> protocol set by virtio_net_hdr_set_proto. Note that since the protocol
> is only checked if skb->dev implements header_ops->parse_protocol,
> packets from devices without the implementation are not checked at this
> stage.
>
> Fixes: 9274124f023b ("net: stricter validation of untrusted gso packets")
> Signed-off-by: Balazs Nemeth <bnemeth@xxxxxxxxxx>
> ---
> include/linux/virtio_net.h | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index e8a924eeea3d..6c478eee0452 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -79,8 +79,14 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
> if (gso_type && skb->network_header) {
> struct flow_keys_basic keys;
>
> - if (!skb->protocol)
> + if (!skb->protocol) {
> + const struct ethhdr *eth = skb_eth_hdr(skb);
> + __be16 etype = dev_parse_header_protocol(skb);
> +
> virtio_net_hdr_set_proto(skb, hdr);
> + if (etype && etype != skb->protocol)
> + return -EINVAL;
> + }
Well the protocol in the header is an attempt at an optimization to
remove need to parse the packet ... any data on whether this
affecs performance?
> retry:
> if (!skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
> NULL, 0, 0, 0,
> --
> 2.29.2
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