On Wed, Apr 20, 2022 at 4:28 AM Hangbin Liu <liuhangbin@xxxxxxxxx> 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(), and move the function in packet_snd() before
> calling virtio_net_hdr_set_proto().
The network header is set in
skb_reset_network_header(skb);
err = -EINVAL;
if (sock->type == SOCK_DGRAM) {
offset = dev_hard_header(skb, dev, ntohs(proto), addr,
NULL, len);
if (unlikely(offset < 0))
goto out_free;
} else if (reserve) {
skb_reserve(skb, -reserve);
if (len < reserve + sizeof(struct ipv6hdr) &&
dev->min_header_len != dev->hard_header_len)
skb_reset_network_header(skb);
}
If all that is needed is to move the network header beyond an optional
VLAN tag in the case of SOCK_RAW, then this can be done in the else
for Ethernet packets.
It is not safe to increase reserve, as that would eat into the
reserved hlen LL_RESERVED_SPACE(dev), which does not account for
optional VLAN headers.
Instead of setting here first, then patching up again later in
packet_parse_headers.
This change affects all packets with VLAN headers, not just those with
GSO. I imagine that moving the network header is safe for all, but
don't know that code well enough to verify that it does not have
unintended side effects. Does dev_queue_xmit expect the network header
to point to the start of the VLAN headers or after, for instance?
> 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 consistence with function packet_sendmsg_spkt().
>
> Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxx>
> ---
> 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 002d2b9c69dd..cfdbda28ef82 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
>
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