// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#define KBUILD_MODNAME "foo"
#include <uapi/linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/if_vlan.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <bpf/bpf_helpers.h>
#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)
struct {
__uint(type, BPF_MAP_TYPE_DEVMAP);
__uint(key_size, sizeof(int));
__uint(value_size, sizeof(int));
__uint(max_entries, 64);
} xdp_tx_ports SEC(".maps");
/* from include/net/ip.h */
static __always_inline int ip_decrease_ttl(struct iphdr *iph)
{
u32 check = (__force u32)iph->check;
check += (__force u32)htons(0x0100);
iph->check = (__force __sum16)(check + (check >= 0xFFFF));
return --iph->ttl;
}
static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
{
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
struct bpf_fib_lookup fib_params;
struct ethhdr *eth = data;
struct ipv6hdr *ip6h;
struct iphdr *iph;
u16 h_proto;
u64 nh_off;
int rc;
nh_off = sizeof(*eth);
if (data + nh_off > data_end)
return XDP_DROP;
__builtin_memset(&fib_params, 0, sizeof(fib_params));
h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_IP)) {
iph = data + nh_off;
if (iph + 1 > data_end)
return XDP_DROP;
if (iph->ttl <= 1)
return XDP_PASS;
fib_params.family = AF_INET;
fib_params.tos = iph->tos;
fib_params.l4_protocol = iph->protocol;
fib_params.sport = 0;
fib_params.dport = 0;
fib_params.tot_len = ntohs(iph->tot_len);
fib_params.ipv4_src = iph->saddr;
fib_params.ipv4_dst = iph->daddr;
} else if (h_proto == htons(ETH_P_IPV6)) {
struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
ip6h = data + nh_off;
if (ip6h + 1 > data_end)
return XDP_DROP;
if (ip6h->hop_limit <= 1)
return XDP_PASS;
fib_params.family = AF_INET6;
fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
fib_params.l4_protocol = ip6h->nexthdr;
fib_params.sport = 0;
fib_params.dport = 0;
fib_params.tot_len = ntohs(ip6h->payload_len);
*src = ip6h->saddr;
*dst = ip6h->daddr;
} else {
return XDP_PASS;
}
fib_params.ifindex = ctx->ingress_ifindex;
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
/*
* Some rc (return codes) from bpf_fib_lookup() are important,
* to understand how this XDP-prog interacts with network stack.
*
* BPF_FIB_LKUP_RET_NO_NEIGH:
* Even if route lookup was a success, then the MAC-addresses are also
* needed. This is obtained from arp/neighbour table, but if table is
* (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid
* doing ARP lookup directly from XDP, then send packet to normal
* network stack via XDP_PASS and expect it will do ARP resolution.
*
* BPF_FIB_LKUP_RET_FWD_DISABLED:
* The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
* setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
* enabled this on ingress device.
*/
if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
/* Verify egress index has been configured as TX-port.
* (Note: User can still have inserted an egress ifindex that
* doesn't support XDP xmit, which will result in packet drops).
*
* Note: lookup in devmap supported since 0cdbb4b09a0.
* If not supported will fail with:
* cannot pass map_type 14 into func bpf_map_lookup_elem#1:
*/
if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
return XDP_PASS;
if (h_proto == htons(ETH_P_IP))
ip_decrease_ttl(iph);
else if (h_proto == htons(ETH_P_IPV6))
ip6h->hop_limit--;
memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
}
return XDP_PASS;
}
SEC("xdp_fwd")
int xdp_fwd_prog(struct xdp_md *ctx)
{
return xdp_fwd_flags(ctx, 0);
}
SEC("xdp_fwd_direct")
int xdp_fwd_direct_prog(struct xdp_md *ctx)
{
return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
}
char _license[] SEC("license") = "GPL";
