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/* SPDX-License-Identifier: GPL-2.0 */
// Code thankfully copied from:
// https://medium.com/swlh/building-a-xdp-express-data-path-based-peering-router-20db4995da66
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>
#include <linux/socket.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_helpers.h>
#include <stdint.h>
#ifndef XDP_ACTION_MAX
#define XDP_ACTION_MAX (XDP_REDIRECT + 1)
#endif
#ifndef memcpy
#define memcpy(dest, src, n) __builtin_memcpy((dest), (src), (n))
#endif
#ifndef AF_INET
#define AF_INET 2
#endif
#ifndef AF_INET6
#define AF_INET6 10
#endif
#ifndef IPV6_FLOWINFO_MASK
#define IPV6_FLOWINFO_MASK bpf_htonl(0x0FFFFFFF)
#endif
/* This is the data record stored in the map */
struct datarec {
__u64 rx_packets;
__u64 rx_bytes;
};
/* Keeps stats per (enum) xdp_action */
struct bpf_map_def SEC("maps") xdp_stats_map = {
.type = BPF_MAP_TYPE_PERCPU_ARRAY,
.key_size = sizeof(__u32),
.value_size = sizeof(struct datarec),
.max_entries = XDP_ACTION_MAX,
};
struct bpf_map_def SEC("maps") tx_port = {
.type = BPF_MAP_TYPE_DEVMAP,
.key_size = sizeof(int),
.value_size = sizeof(int),
.max_entries = 256,
};
/* from include/net/ip.h */
static __always_inline int ip_decrease_ttl(struct iphdr *iph)
{
__u32 check = iph->check;
check += bpf_htons(0x0100);
iph->check = (__u16)(check + (check >= 0xFFFF));
return --iph->ttl;
}
static __always_inline
__u32 xdp_stats_record_action(struct xdp_md *ctx, __u32 action)
{
if (action >= XDP_ACTION_MAX)
return XDP_ABORTED;
/* Lookup in kernel BPF-side return pointer to actual data record */
struct datarec *rec = bpf_map_lookup_elem(&xdp_stats_map, &action);
if (!rec)
return XDP_ABORTED;
/* BPF_MAP_TYPE_PERCPU_ARRAY returns a data record specific to current
* CPU and XDP hooks runs under Softirq, which makes it safe to update
* without atomic operations.
*/
rec->rx_packets++;
rec->rx_bytes += (ctx->data_end - ctx->data);
return action;
}
/* xdp_router is the name of the xdp program */
SEC("prog")
int xdp_router_func(struct xdp_md *ctx)
{
/* this is the packet context*/
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;
/* default action is to pass */
int action = XDP_PASS;
nh_off = sizeof(*eth);
if (data + nh_off > data_end) {
action = XDP_DROP;
goto out;
}
/* determine if this is IP4 or IPv6 by looking at the Ethernet protocol field */
h_proto = eth->h_proto;
if (h_proto == bpf_htons(ETH_P_IP)) {
/* IPv4 part of the code */
iph = data + nh_off;
if (iph + 1 > data_end) {
action = XDP_DROP;
goto out;
}
/* as a real router, we need to check the TTL to prevent never ending loops*/
if (iph->ttl <= 1)
goto out;
/* populate the fib_params fields to prepare for the lookup */
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 = bpf_ntohs(iph->tot_len);
fib_params.ipv4_src = iph->saddr;
fib_params.ipv4_dst = iph->daddr;
} else if (h_proto == bpf_htons(ETH_P_IPV6)) {
/* IPv6 part of the code */
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) {
action = XDP_DROP;
goto out;
}
/* as a real router, we need to check the TTL to prevent never ending loops*/
if (ip6h->hop_limit <= 1)
goto out;
/* populate the fib_params fields to prepare for the lookup */
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 = bpf_ntohs(ip6h->payload_len);
*src = ip6h->saddr;
*dst = ip6h->daddr;
} else {
goto out;
}
fib_params.ifindex = ctx->ingress_ifindex;
/* this is where the FIB lookup happens. If the lookup is successful */
/* it will populate the fib_params.ifindex with the egress interface index */
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), 0);
switch (rc) {
case BPF_FIB_LKUP_RET_SUCCESS: /* lookup successful */
/* we are a router, so we need to decrease the ttl */
if (h_proto == bpf_htons(ETH_P_IP))
ip_decrease_ttl(iph);
else if (h_proto == bpf_htons(ETH_P_IPV6))
ip6h->hop_limit--;
/* set the correct new source and destionation mac addresses */
/* can be found in fib_params.dmac and fib_params.smac */
memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
/* and done, now we set the action to bpf_redirect_map with fib_params.ifindex which is the egress port as paramater */
action = bpf_redirect_map(&tx_port, fib_params.ifindex, 0);
break;
case BPF_FIB_LKUP_RET_BLACKHOLE: /* dest is blackholed; can be dropped */
case BPF_FIB_LKUP_RET_UNREACHABLE: /* dest is unreachable; can be dropped */
case BPF_FIB_LKUP_RET_PROHIBIT: /* dest not allowed; can be dropped */
action = XDP_DROP;
break;
case BPF_FIB_LKUP_RET_NOT_FWDED: /* packet is not forwarded */
case BPF_FIB_LKUP_RET_FWD_DISABLED: /* fwding is not enabled on ingress */
case BPF_FIB_LKUP_RET_UNSUPP_LWT: /* fwd requires encapsulation */
case BPF_FIB_LKUP_RET_NO_NEIGH: /* no neighbor entry for nh */
case BPF_FIB_LKUP_RET_FRAG_NEEDED: /* fragmentation required to fwd */
/* PASS */
break;
}
out:
/* and done, update stats and return action */
return xdp_stats_record_action(ctx, action);
}
char _license[] SEC("license") = "GPL";
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