Re: [PATCHv2 net-next] net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 25, 2022 at 09:45:02AM +0800, Hangbin Liu wrote:
> Currently, the kernel drops GSO VLAN tagged packet if it's created with
> socket(AF_PACKET, SOCK_RAW, 0) plus virtio_net_hdr.
> 
> The reason is AF_PACKET doesn't adjust the skb network header if there is
> a VLAN tag. Then after virtio_net_hdr_set_proto() called, the skb->protocol
> will be set to ETH_P_IP/IPv6. And in later inet/ipv6_gso_segment() the skb
> is dropped as network header position is invalid.
> 
> Let's handle VLAN packets by adjusting network header position in
> packet_parse_headers(). The adjustment is safe and does not affect the
> later xmit as tap device also did that.
> 
> In packet_snd(), packet_parse_headers() need to be moved before calling
> virtio_net_hdr_set_proto(), so we can set correct skb->protocol and
> network header first.
> 
> There is no need to update tpacket_snd() as it calls packet_parse_headers()
> in tpacket_fill_skb(), which is already before calling virtio_net_hdr_*
> functions.
> 
> skb->no_fcs setting is also moved upper to make all skb settings together
> and keep consistency with function packet_sendmsg_spkt().
> 
> Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> 
> v2: Rewrite commit description, no code update.
> ---
>  net/packet/af_packet.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 243566129784..fd31334cf688 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1924,12 +1924,20 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,
>  
>  static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
>  {
> +	int depth;
> +
>  	if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) &&
>  	    sock->type == SOCK_RAW) {
>  		skb_reset_mac_header(skb);
>  		skb->protocol = dev_parse_header_protocol(skb);
>  	}
>  
> +	/* Move network header to the right position for VLAN tagged packets */
> +	if (likely(skb->dev->type == ARPHRD_ETHER) &&
> +	    eth_type_vlan(skb->protocol) &&
> +	    __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
> +		skb_set_network_header(skb, depth);
> +
>  	skb_probe_transport_header(skb);
>  }
>  
> @@ -3047,6 +3055,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>  	skb->mark = sockc.mark;
>  	skb->tstamp = sockc.transmit_time;
>  
> +	if (unlikely(extra_len == 4))
> +		skb->no_fcs = 1;
> +
> +	packet_parse_headers(skb, sock);
> +
>  	if (has_vnet_hdr) {
>  		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
>  		if (err)
> @@ -3055,11 +3068,6 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>  		virtio_net_hdr_set_proto(skb, &vnet_hdr);
>  	}
>  
> -	packet_parse_headers(skb, sock);
> -
> -	if (unlikely(extra_len == 4))
> -		skb->no_fcs = 1;
> -
>  	err = po->xmit(skb);
>  	if (unlikely(err != 0)) {
>  		if (err > 0)
> -- 
> 2.35.1