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// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2019 Cloudflare Ltd.
// Copyright (c) 2020 Isovalent, Inc.
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/pkt_cls.h>
#include <linux/tcp.h>
#include <sys/socket.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
/* Pin map under /sys/fs/bpf/tc/globals/<map name> */
#define PIN_GLOBAL_NS 2
/* Must match struct bpf_elf_map layout from iproute2 */
struct {
__u32 type;
__u32 size_key;
__u32 size_value;
__u32 max_elem;
__u32 flags;
__u32 id;
__u32 pinning;
} server_map SEC("maps") = {
.type = BPF_MAP_TYPE_SOCKMAP,
.size_key = sizeof(int),
.size_value = sizeof(__u64),
.max_elem = 1,
.pinning = PIN_GLOBAL_NS,
};
char _license[] SEC("license") = "GPL";
/* Fill 'tuple' with L3 info, and attempt to find L4. On fail, return NULL. */
static inline struct bpf_sock_tuple *
get_tuple(struct __sk_buff *skb, bool *ipv4, bool *tcp)
{
void *data_end = (void *)(long)skb->data_end;
void *data = (void *)(long)skb->data;
struct bpf_sock_tuple *result;
struct ethhdr *eth;
__u64 tuple_len;
__u8 proto = 0;
__u64 ihl_len;
eth = (struct ethhdr *)(data);
if (eth + 1 > data_end)
return NULL;
if (eth->h_proto == bpf_htons(ETH_P_IP)) {
struct iphdr *iph = (struct iphdr *)(data + sizeof(*eth));
if (iph + 1 > data_end)
return NULL;
if (iph->ihl != 5)
/* Options are not supported */
return NULL;
ihl_len = iph->ihl * 4;
proto = iph->protocol;
*ipv4 = true;
result = (struct bpf_sock_tuple *)&iph->saddr;
} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
struct ipv6hdr *ip6h = (struct ipv6hdr *)(data + sizeof(*eth));
if (ip6h + 1 > data_end)
return NULL;
ihl_len = sizeof(*ip6h);
proto = ip6h->nexthdr;
*ipv4 = false;
result = (struct bpf_sock_tuple *)&ip6h->saddr;
} else {
return (struct bpf_sock_tuple *)data;
}
if (proto != IPPROTO_TCP && proto != IPPROTO_UDP)
return NULL;
*tcp = (proto == IPPROTO_TCP);
return result;
}
static inline int
handle_udp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
{
struct bpf_sock *sk;
const int zero = 0;
size_t tuple_len;
__be16 dport;
int ret;
tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
return TC_ACT_SHOT;
sk = bpf_sk_lookup_udp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
if (sk)
goto assign;
dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
if (dport != bpf_htons(4321))
return TC_ACT_OK;
sk = bpf_map_lookup_elem(&server_map, &zero);
if (!sk)
return TC_ACT_SHOT;
assign:
ret = bpf_sk_assign(skb, sk, 0);
bpf_sk_release(sk);
return ret;
}
static inline int
handle_tcp(struct __sk_buff *skb, struct bpf_sock_tuple *tuple, bool ipv4)
{
struct bpf_sock *sk;
const int zero = 0;
size_t tuple_len;
__be16 dport;
int ret;
tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
if ((void *)tuple + tuple_len > (void *)(long)skb->data_end)
return TC_ACT_SHOT;
sk = bpf_skc_lookup_tcp(skb, tuple, tuple_len, BPF_F_CURRENT_NETNS, 0);
if (sk) {
if (sk->state != BPF_TCP_LISTEN)
goto assign;
bpf_sk_release(sk);
}
dport = ipv4 ? tuple->ipv4.dport : tuple->ipv6.dport;
if (dport != bpf_htons(4321))
return TC_ACT_OK;
sk = bpf_map_lookup_elem(&server_map, &zero);
if (!sk)
return TC_ACT_SHOT;
if (sk->state != BPF_TCP_LISTEN) {
bpf_sk_release(sk);
return TC_ACT_SHOT;
}
assign:
ret = bpf_sk_assign(skb, sk, 0);
bpf_sk_release(sk);
return ret;
}
SEC("tc")
int bpf_sk_assign_test(struct __sk_buff *skb)
{
struct bpf_sock_tuple *tuple;
bool ipv4 = false;
bool tcp = false;
int tuple_len;
int ret = 0;
tuple = get_tuple(skb, &ipv4, &tcp);
if (!tuple)
return TC_ACT_SHOT;
/* Note that the verifier socket return type for bpf_skc_lookup_tcp()
* differs from bpf_sk_lookup_udp(), so even though the C-level type is
* the same here, if we try to share the implementations they will
* fail to verify because we're crossing pointer types.
*/
if (tcp)
ret = handle_tcp(skb, tuple, ipv4);
else
ret = handle_udp(skb, tuple, ipv4);
return ret == 0 ? TC_ACT_OK : TC_ACT_SHOT;
}
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