// SPDX-License-Identifier: GPL-2.0
#include <limits.h>
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <linux/pkt_cls.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/icmp.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/if_packet.h>
#include <sys/socket.h>
#include <linux/if_tunnel.h>
#include <linux/mpls.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

#define PROG(F) PROG_(F, _##F)
#define PROG_(NUM, NAME) SEC("flow_dissector") int flow_dissector_##NUM

/* These are the identifiers of the BPF programs that will be used in tail
 * calls. Name is limited to 16 characters, with the terminating character and
 * bpf_func_ above, we have only 6 to work with, anything after will be cropped.
 */
#define IP		0
#define IPV6		1
#define IPV6OP		2 /* Destination/Hop-by-Hop Options IPv6 Ext. Header */
#define IPV6FR		3 /* Fragmentation IPv6 Extension Header */
#define MPLS		4
#define VLAN		5
#define MAX_PROG	6

#define IP_MF		0x2000
#define IP_OFFSET	0x1FFF
#define IP6_MF		0x0001
#define IP6_OFFSET	0xFFF8

struct vlan_hdr {
	__be16 h_vlan_TCI;
	__be16 h_vlan_encapsulated_proto;
};

struct gre_hdr {
	__be16 flags;
	__be16 proto;
};

struct frag_hdr {
	__u8 nexthdr;
	__u8 reserved;
	__be16 frag_off;
	__be32 identification;
};

struct {
	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
	__uint(max_entries, MAX_PROG);
	__uint(key_size, sizeof(__u32));
	__uint(value_size, sizeof(__u32));
} jmp_table SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_HASH);
	__uint(max_entries, 1024);
	__type(key, __u32);
	__type(value, struct bpf_flow_keys);
} last_dissection SEC(".maps");

static __always_inline int export_flow_keys(struct bpf_flow_keys *keys,
					    int ret)
{
	__u32 key = (__u32)(keys->sport) << 16 | keys->dport;
	struct bpf_flow_keys val;

	memcpy(&val, keys, sizeof(val));
	bpf_map_update_elem(&last_dissection, &key, &val, BPF_ANY);
	return ret;
}

#define IPV6_FLOWLABEL_MASK		__bpf_constant_htonl(0x000FFFFF)
static inline __be32 ip6_flowlabel(const struct ipv6hdr *hdr)
{
	return *(__be32 *)hdr & IPV6_FLOWLABEL_MASK;
}

static __always_inline void *bpf_flow_dissect_get_header(struct __sk_buff *skb,
							 __u16 hdr_size,
							 void *buffer)
{
	void *data_end = (void *)(long)skb->data_end;
	void *data = (void *)(long)skb->data;
	__u16 thoff = skb->flow_keys->thoff;
	__u8 *hdr;

	/* Verifies this variable offset does not overflow */
	if (thoff > (USHRT_MAX - hdr_size))
		return NULL;

	hdr = data + thoff;
	if (hdr + hdr_size <= data_end)
		return hdr;

	if (bpf_skb_load_bytes(skb, thoff, buffer, hdr_size))
		return NULL;

	return buffer;
}

/* Dispatches on ETHERTYPE */
static __always_inline int parse_eth_proto(struct __sk_buff *skb, __be16 proto)
{
	struct bpf_flow_keys *keys = skb->flow_keys;

	switch (proto) {
	case bpf_htons(ETH_P_IP):
		bpf_tail_call_static(skb, &jmp_table, IP);
		break;
	case bpf_htons(ETH_P_IPV6):
		bpf_tail_call_static(skb, &jmp_table, IPV6);
		break;
	case bpf_htons(ETH_P_MPLS_MC):
	case bpf_htons(ETH_P_MPLS_UC):
		bpf_tail_call_static(skb, &jmp_table, MPLS);
		break;
	case bpf_htons(ETH_P_8021Q):
	case bpf_htons(ETH_P_8021AD):
		bpf_tail_call_static(skb, &jmp_table, VLAN);
		break;
	default:
		/* Protocol not supported */
		return export_flow_keys(keys, BPF_DROP);
	}

	return export_flow_keys(keys, BPF_DROP);
}

SEC("flow_dissector")
int _dissect(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;

	return parse_eth_proto(skb, keys->n_proto);
}

/* Parses on IPPROTO_* */
static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	void *data_end = (void *)(long)skb->data_end;
	struct icmphdr *icmp, _icmp;
	struct gre_hdr *gre, _gre;
	struct ethhdr *eth, _eth;
	struct tcphdr *tcp, _tcp;
	struct udphdr *udp, _udp;

	switch (proto) {
	case IPPROTO_ICMP:
		icmp = bpf_flow_dissect_get_header(skb, sizeof(*icmp), &_icmp);
		if (!icmp)
			return export_flow_keys(keys, BPF_DROP);
		return export_flow_keys(keys, BPF_OK);
	case IPPROTO_IPIP:
		keys->is_encap = true;
		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
			return export_flow_keys(keys, BPF_OK);

		return parse_eth_proto(skb, bpf_htons(ETH_P_IP));
	case IPPROTO_IPV6:
		keys->is_encap = true;
		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
			return export_flow_keys(keys, BPF_OK);

		return parse_eth_proto(skb, bpf_htons(ETH_P_IPV6));
	case IPPROTO_GRE:
		gre = bpf_flow_dissect_get_header(skb, sizeof(*gre), &_gre);
		if (!gre)
			return export_flow_keys(keys, BPF_DROP);

		if (bpf_htons(gre->flags & GRE_VERSION))
			/* Only inspect standard GRE packets with version 0 */
			return export_flow_keys(keys, BPF_OK);

		keys->thoff += sizeof(*gre); /* Step over GRE Flags and Proto */
		if (GRE_IS_CSUM(gre->flags))
			keys->thoff += 4; /* Step over chksum and Padding */
		if (GRE_IS_KEY(gre->flags))
			keys->thoff += 4; /* Step over key */
		if (GRE_IS_SEQ(gre->flags))
			keys->thoff += 4; /* Step over sequence number */

		keys->is_encap = true;
		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
			return export_flow_keys(keys, BPF_OK);

		if (gre->proto == bpf_htons(ETH_P_TEB)) {
			eth = bpf_flow_dissect_get_header(skb, sizeof(*eth),
							  &_eth);
			if (!eth)
				return export_flow_keys(keys, BPF_DROP);

			keys->thoff += sizeof(*eth);

			return parse_eth_proto(skb, eth->h_proto);
		} else {
			return parse_eth_proto(skb, gre->proto);
		}
	case IPPROTO_TCP:
		tcp = bpf_flow_dissect_get_header(skb, sizeof(*tcp), &_tcp);
		if (!tcp)
			return export_flow_keys(keys, BPF_DROP);

		if (tcp->doff < 5)
			return export_flow_keys(keys, BPF_DROP);

		if ((__u8 *)tcp + (tcp->doff << 2) > data_end)
			return export_flow_keys(keys, BPF_DROP);

		keys->sport = tcp->source;
		keys->dport = tcp->dest;
		return export_flow_keys(keys, BPF_OK);
	case IPPROTO_UDP:
	case IPPROTO_UDPLITE:
		udp = bpf_flow_dissect_get_header(skb, sizeof(*udp), &_udp);
		if (!udp)
			return export_flow_keys(keys, BPF_DROP);

		keys->sport = udp->source;
		keys->dport = udp->dest;
		return export_flow_keys(keys, BPF_OK);
	default:
		return export_flow_keys(keys, BPF_DROP);
	}

	return export_flow_keys(keys, BPF_DROP);
}

static __always_inline int parse_ipv6_proto(struct __sk_buff *skb, __u8 nexthdr)
{
	struct bpf_flow_keys *keys = skb->flow_keys;

	switch (nexthdr) {
	case IPPROTO_HOPOPTS:
	case IPPROTO_DSTOPTS:
		bpf_tail_call_static(skb, &jmp_table, IPV6OP);
		break;
	case IPPROTO_FRAGMENT:
		bpf_tail_call_static(skb, &jmp_table, IPV6FR);
		break;
	default:
		return parse_ip_proto(skb, nexthdr);
	}

	return export_flow_keys(keys, BPF_DROP);
}

PROG(IP)(struct __sk_buff *skb)
{
	void *data_end = (void *)(long)skb->data_end;
	struct bpf_flow_keys *keys = skb->flow_keys;
	void *data = (void *)(long)skb->data;
	struct iphdr *iph, _iph;
	bool done = false;

	iph = bpf_flow_dissect_get_header(skb, sizeof(*iph), &_iph);
	if (!iph)
		return export_flow_keys(keys, BPF_DROP);

	/* IP header cannot be smaller than 20 bytes */
	if (iph->ihl < 5)
		return export_flow_keys(keys, BPF_DROP);

	keys->addr_proto = ETH_P_IP;
	keys->ipv4_src = iph->saddr;
	keys->ipv4_dst = iph->daddr;
	keys->ip_proto = iph->protocol;

	keys->thoff += iph->ihl << 2;
	if (data + keys->thoff > data_end)
		return export_flow_keys(keys, BPF_DROP);

	if (iph->frag_off & bpf_htons(IP_MF | IP_OFFSET)) {
		keys->is_frag = true;
		if (iph->frag_off & bpf_htons(IP_OFFSET)) {
			/* From second fragment on, packets do not have headers
			 * we can parse.
			 */
			done = true;
		} else {
			keys->is_first_frag = true;
			/* No need to parse fragmented packet unless
			 * explicitly asked for.
			 */
			if (!(keys->flags &
			      BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
				done = true;
		}
	}

	if (done)
		return export_flow_keys(keys, BPF_OK);

	return parse_ip_proto(skb, iph->protocol);
}

PROG(IPV6)(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	struct ipv6hdr *ip6h, _ip6h;

	ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
	if (!ip6h)
		return export_flow_keys(keys, BPF_DROP);

	keys->addr_proto = ETH_P_IPV6;
	memcpy(&keys->ipv6_src, &ip6h->saddr, 2*sizeof(ip6h->saddr));

	keys->thoff += sizeof(struct ipv6hdr);
	keys->ip_proto = ip6h->nexthdr;
	keys->flow_label = ip6_flowlabel(ip6h);

	if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL)
		return export_flow_keys(keys, BPF_OK);

	return parse_ipv6_proto(skb, ip6h->nexthdr);
}

PROG(IPV6OP)(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	struct ipv6_opt_hdr *ip6h, _ip6h;

	ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
	if (!ip6h)
		return export_flow_keys(keys, BPF_DROP);

	/* hlen is in 8-octets and does not include the first 8 bytes
	 * of the header
	 */
	keys->thoff += (1 + ip6h->hdrlen) << 3;
	keys->ip_proto = ip6h->nexthdr;

	return parse_ipv6_proto(skb, ip6h->nexthdr);
}

PROG(IPV6FR)(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	struct frag_hdr *fragh, _fragh;

	fragh = bpf_flow_dissect_get_header(skb, sizeof(*fragh), &_fragh);
	if (!fragh)
		return export_flow_keys(keys, BPF_DROP);

	keys->thoff += sizeof(*fragh);
	keys->is_frag = true;
	keys->ip_proto = fragh->nexthdr;

	if (!(fragh->frag_off & bpf_htons(IP6_OFFSET))) {
		keys->is_first_frag = true;

		/* No need to parse fragmented packet unless
		 * explicitly asked for.
		 */
		if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
			return export_flow_keys(keys, BPF_OK);
	} else {
		return export_flow_keys(keys, BPF_OK);
	}

	return parse_ipv6_proto(skb, fragh->nexthdr);
}

PROG(MPLS)(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	struct mpls_label *mpls, _mpls;

	mpls = bpf_flow_dissect_get_header(skb, sizeof(*mpls), &_mpls);
	if (!mpls)
		return export_flow_keys(keys, BPF_DROP);

	return export_flow_keys(keys, BPF_OK);
}

PROG(VLAN)(struct __sk_buff *skb)
{
	struct bpf_flow_keys *keys = skb->flow_keys;
	struct vlan_hdr *vlan, _vlan;

	/* Account for double-tagging */
	if (keys->n_proto == bpf_htons(ETH_P_8021AD)) {
		vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
		if (!vlan)
			return export_flow_keys(keys, BPF_DROP);

		if (vlan->h_vlan_encapsulated_proto != bpf_htons(ETH_P_8021Q))
			return export_flow_keys(keys, BPF_DROP);

		keys->nhoff += sizeof(*vlan);
		keys->thoff += sizeof(*vlan);
	}

	vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
	if (!vlan)
		return export_flow_keys(keys, BPF_DROP);

	keys->nhoff += sizeof(*vlan);
	keys->thoff += sizeof(*vlan);
	/* Only allow 8021AD + 8021Q double tagging and no triple tagging.*/
	if (vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021AD) ||
	    vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021Q))
		return export_flow_keys(keys, BPF_DROP);

	keys->n_proto = vlan->h_vlan_encapsulated_proto;
	return parse_eth_proto(skb, vlan->h_vlan_encapsulated_proto);
}

char __license[] SEC("license") = "GPL";