Tizian-Maxime-Weigt/l3-l4-forwarding-in-xdp
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Tizian Maxime Weigt 2025-10-27 16:07:20 +00:00
parent d06eab0a55
commit 319bc67f33
1 changed files with 113 additions and 23 deletions
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134
main.c
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@ -6,11 +6,14 @@
#include <linux/if_vlan.h> #include <linux/if_vlan.h>
#include <linux/ip.h> #include <linux/ip.h>
#include <linux/ipv6.h> #include <linux/ipv6.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <bpf/bpf_helpers.h> #include <bpf/bpf_helpers.h>
#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF) #define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)
/* Forwarding ports */
struct bpf_map_def SEC("maps") xdp_l3fwd_ports = { struct bpf_map_def SEC("maps") xdp_l3fwd_ports = {
.type = BPF_MAP_TYPE_DEVMAP, .type = BPF_MAP_TYPE_DEVMAP,
.key_size = sizeof(int), .key_size = sizeof(int),
@ -18,15 +21,63 @@ struct bpf_map_def SEC("maps") xdp_l3fwd_ports = {
.max_entries = 512, .max_entries = 512,
}; };
/* Stats key — identifies a connection or flow */
struct flow_key {
__u8 proto;
__u8 pad[3]; /* alignment */
union {
__u32 ipv4_src;
__u8 ipv6_src[16];
};
union {
__u32 ipv4_dst;
__u8 ipv6_dst[16];
};
__u16 sport;
__u16 dport;
};
/* Stats value — counts packets and bytes */
struct flow_stats {
__u64 packets;
__u64 bytes;
};
/* Hash map to track stats per flow */
struct bpf_map_def SEC("maps") xdp_flow_stats = {
.type = BPF_MAP_TYPE_HASH,
.key_size = sizeof(struct flow_key),
.value_size = sizeof(struct flow_stats),
.max_entries = 65536,
};
/* Decrease IPv4 TTL helper */
static __always_inline int ip_decrease_ttl(struct iphdr *iph) static __always_inline int ip_decrease_ttl(struct iphdr *iph)
{ {
u32 check = (__force u32)iph->check; u32 check = (__force u32)iph->check;
check += (__force u32)htons(0x0100); check += (__force u32)htons(0x0100);
iph->check = (__force __sum16)(check + (check >= 0xFFFF)); iph->check = (__force __sum16)(check + (check >= 0xFFFF));
return --iph->ttl; return --iph->ttl;
} }
/* Record stats in the xdp_flow_stats map */
static __always_inline void record_stats(struct xdp_md *ctx, struct flow_key *key, __u64 bytes)
{
struct flow_stats *stats;
stats = bpf_map_lookup_elem(&xdp_flow_stats, key);
if (stats) {
__sync_fetch_and_add(&stats->packets, 1);
__sync_fetch_and_add(&stats->bytes, bytes);
} else {
struct flow_stats new_stats = {
.packets = 1,
.bytes = bytes,
};
bpf_map_update_elem(&xdp_flow_stats, key, &new_stats, BPF_ANY);
}
}
static __always_inline int xdp_l3fwd_flags(struct xdp_md *ctx, u32 flags) static __always_inline int xdp_l3fwd_flags(struct xdp_md *ctx, u32 flags)
{ {
void *data_end = (void *)(long)ctx->data_end; void *data_end = (void *)(long)ctx->data_end;
@ -44,46 +95,85 @@ static __always_inline int xdp_l3fwd_flags(struct xdp_md *ctx, u32 flags)
return XDP_DROP; return XDP_DROP;
__builtin_memset(&fib_params, 0, sizeof(fib_params)); __builtin_memset(&fib_params, 0, sizeof(fib_params));
h_proto = eth->h_proto; h_proto = eth->h_proto;
struct flow_key key = {};
__u64 bytes = data_end - data;
if (h_proto == htons(ETH_P_IP)) { if (h_proto == htons(ETH_P_IP)) {
iph = data + nh_off; iph = data + nh_off;
if ((void *)(iph + 1) > data_end)
if (iph + 1 > data_end)
return XDP_DROP; return XDP_DROP;
key.proto = iph->protocol;
key.ipv4_src = iph->saddr;
key.ipv4_dst = iph->daddr;
void *l4_hdr = (void *)iph + (iph->ihl * 4);
if (l4_hdr + sizeof(struct udphdr) <= data_end) {
if (iph->protocol == IPPROTO_TCP) {
struct tcphdr *tcph = l4_hdr;
key.sport = tcph->source;
key.dport = tcph->dest;
} else if (iph->protocol == IPPROTO_UDP) {
struct udphdr *udph = l4_hdr;
key.sport = udph->source;
key.dport = udph->dest;
}
}
/* Record stats before forwarding */
record_stats(ctx, &key, bytes);
if (iph->ttl <= 1) if (iph->ttl <= 1)
return XDP_PASS; return XDP_PASS;
fib_params.family = AF_INET; fib_params.family = AF_INET;
fib_params.tos = iph->tos; fib_params.tos = iph->tos;
fib_params.l4_protocol = iph->protocol; fib_params.l4_protocol = iph->protocol;
fib_params.tot_len = ntohs(iph->tot_len); fib_params.tot_len = ntohs(iph->tot_len);
fib_params.ipv4_src = iph->saddr; fib_params.ipv4_src = iph->saddr;
fib_params.ipv4_dst = iph->daddr; 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;
} else if (h_proto == htons(ETH_P_IPV6)) {
ip6h = data + nh_off; ip6h = data + nh_off;
if (ip6h + 1 > data_end) if ((void *)(ip6h + 1) > data_end)
return XDP_DROP; return XDP_DROP;
key.proto = ip6h->nexthdr;
__builtin_memcpy(key.ipv6_src, &ip6h->saddr, 16);
__builtin_memcpy(key.ipv6_dst, &ip6h->daddr, 16);
void *l4_hdr = (void *)(ip6h + 1);
if (l4_hdr + sizeof(struct udphdr) <= data_end) {
if (ip6h->nexthdr == IPPROTO_TCP) {
struct tcphdr *tcph = l4_hdr;
key.sport = tcph->source;
key.dport = tcph->dest;
} else if (ip6h->nexthdr == IPPROTO_UDP) {
struct udphdr *udph = l4_hdr;
key.sport = udph->source;
key.dport = udph->dest;
}
}
/* Record stats before forwarding */
record_stats(ctx, &key, bytes);
if (ip6h->hop_limit <= 1) if (ip6h->hop_limit <= 1)
return XDP_PASS; return XDP_PASS;
fib_params.family = AF_INET6; fib_params.family = AF_INET6;
fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK; fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
fib_params.l4_protocol = ip6h->nexthdr; fib_params.l4_protocol = ip6h->nexthdr;
fib_params.tot_len = ntohs(ip6h->payload_len); fib_params.tot_len = ntohs(ip6h->payload_len);
*src = ip6h->saddr; __builtin_memcpy(fib_params.ipv6_src, &ip6h->saddr, 16);
*dst = ip6h->daddr; __builtin_memcpy(fib_params.ipv6_dst, &ip6h->daddr, 16);
} else { } else {
return XDP_PASS; return XDP_PASS;
} }
fib_params.ifindex = ctx->ingress_ifindex; fib_params.ifindex = ctx->ingress_ifindex;
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags); rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
if (rc == BPF_FIB_LKUP_RET_SUCCESS) { if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
if (!bpf_map_lookup_elem(&xdp_l3fwd_ports, &fib_params.ifindex)) if (!bpf_map_lookup_elem(&xdp_l3fwd_ports, &fib_params.ifindex))