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Commit 9c98b13c authored by Petar Penkov's avatar Petar Penkov Committed by Alexei Starovoitov
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flow_dissector: implements eBPF parser 

This eBPF program extracts basic/control/ip address/ports keys from
incoming packets. It supports recursive parsing for IP encapsulation,
and VLAN, along with IPv4/IPv6 and extension headers.  This program is
meant to show how flow dissection and key extraction can be done in
eBPF.

Link: http://vger.kernel.org/netconf2017_files/rx_hardening_and_udp_gso.pdf


Signed-off-by: default avatarPetar Penkov <ppenkov@google.com>
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent c22fbae7

tools/testing/selftests/bpf/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test 
	test_get_stack_rawtp.o test_sockmap_kern.o test_sockhash_kern.o \

	test_lwt_seg6local.o sendmsg4_prog.o sendmsg6_prog.o test_lirc_mode2_kern.o \

	get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \

	test_skb_cgroup_id_kern.o

	test_skb_cgroup_id_kern.o bpf_flow.o



# Order correspond to 'make run_tests' order

TEST_PROGS := test_kmod.sh \

tools/testing/selftests/bpf/bpf_flow.c

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+373 −0
Original line number Diff line number Diff line 
// 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_helpers.h"

#include "bpf_endian.h"



int _version SEC("version") = 1;

#define PROG(F) SEC(#F) int bpf_func_##F



/* 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.

 */

enum {

	IP,

	IPV6,

	IPV6OP,	/* Destination/Hop-by-Hop Options IPv6 Extension header */

	IPV6FR,	/* Fragmentation IPv6 Extension Header */

	MPLS,

	VLAN,

};



#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 bpf_map_def SEC("maps") jmp_table = {

	.type = BPF_MAP_TYPE_PROG_ARRAY,

	.key_size = sizeof(__u32),

	.value_size = sizeof(__u32),

	.max_entries = 8

};



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 nhoff = skb->flow_keys->nhoff;

	__u8 *hdr;



	/* Verifies this variable offset does not overflow */

	if (nhoff > (USHRT_MAX - hdr_size))

		return NULL;



	hdr = data + nhoff;

	if (hdr + hdr_size <= data_end)

		return hdr;



	if (bpf_skb_load_bytes(skb, nhoff, 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;



	keys->n_proto = proto;

	switch (proto) {

	case bpf_htons(ETH_P_IP):

		bpf_tail_call(skb, &jmp_table, IP);

		break;

	case bpf_htons(ETH_P_IPV6):

		bpf_tail_call(skb, &jmp_table, IPV6);

		break;

	case bpf_htons(ETH_P_MPLS_MC):

	case bpf_htons(ETH_P_MPLS_UC):

		bpf_tail_call(skb, &jmp_table, MPLS);

		break;

	case bpf_htons(ETH_P_8021Q):

	case bpf_htons(ETH_P_8021AD):

		bpf_tail_call(skb, &jmp_table, VLAN);

		break;

	default:

		/* Protocol not supported */

		return BPF_DROP;

	}



	return BPF_DROP;

}



SEC("dissect")

int dissect(struct __sk_buff *skb)

{

	if (!skb->vlan_present)

		return parse_eth_proto(skb, skb->protocol);

	else

		return parse_eth_proto(skb, skb->vlan_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;



	keys->ip_proto = proto;

	switch (proto) {

	case IPPROTO_ICMP:

		icmp = bpf_flow_dissect_get_header(skb, sizeof(*icmp), &_icmp);

		if (!icmp)

			return BPF_DROP;

		return BPF_OK;

	case IPPROTO_IPIP:

		keys->is_encap = true;

		return parse_eth_proto(skb, bpf_htons(ETH_P_IP));

	case IPPROTO_IPV6:

		keys->is_encap = true;

		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 BPF_DROP;



		if (bpf_htons(gre->flags & GRE_VERSION))

			/* Only inspect standard GRE packets with version 0 */

			return BPF_OK;



		keys->nhoff += sizeof(*gre); /* Step over GRE Flags and Proto */

		if (GRE_IS_CSUM(gre->flags))

			keys->nhoff += 4; /* Step over chksum and Padding */

		if (GRE_IS_KEY(gre->flags))

			keys->nhoff += 4; /* Step over key */

		if (GRE_IS_SEQ(gre->flags))

			keys->nhoff += 4; /* Step over sequence number */



		keys->is_encap = true;



		if (gre->proto == bpf_htons(ETH_P_TEB)) {

			eth = bpf_flow_dissect_get_header(skb, sizeof(*eth),

							  &_eth);

			if (!eth)

				return BPF_DROP;



			keys->nhoff += 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 BPF_DROP;



		if (tcp->doff < 5)

			return BPF_DROP;



		if ((__u8 *)tcp + (tcp->doff << 2) > data_end)

			return BPF_DROP;



		keys->thoff = keys->nhoff;

		keys->sport = tcp->source;

		keys->dport = tcp->dest;

		return BPF_OK;

	case IPPROTO_UDP:

	case IPPROTO_UDPLITE:

		udp = bpf_flow_dissect_get_header(skb, sizeof(*udp), &_udp);

		if (!udp)

			return BPF_DROP;



		keys->thoff = keys->nhoff;

		keys->sport = udp->source;

		keys->dport = udp->dest;

		return BPF_OK;

	default:

		return BPF_DROP;

	}



	return BPF_DROP;

}



static __always_inline int parse_ipv6_proto(struct __sk_buff *skb, __u8 nexthdr)

{

	struct bpf_flow_keys *keys = skb->flow_keys;



	keys->ip_proto = nexthdr;

	switch (nexthdr) {

	case IPPROTO_HOPOPTS:

	case IPPROTO_DSTOPTS:

		bpf_tail_call(skb, &jmp_table, IPV6OP);

		break;

	case IPPROTO_FRAGMENT:

		bpf_tail_call(skb, &jmp_table, IPV6FR);

		break;

	default:

		return parse_ip_proto(skb, nexthdr);

	}



	return 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 BPF_DROP;



	/* IP header cannot be smaller than 20 bytes */

	if (iph->ihl < 5)

		return BPF_DROP;



	keys->addr_proto = ETH_P_IP;

	keys->ipv4_src = iph->saddr;

	keys->ipv4_dst = iph->daddr;



	keys->nhoff += iph->ihl << 2;

	if (data + keys->nhoff > data_end)

		return 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;

	}



	if (done)

		return 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 BPF_DROP;



	keys->addr_proto = ETH_P_IPV6;

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



	keys->nhoff += sizeof(struct ipv6hdr);



	return parse_ipv6_proto(skb, ip6h->nexthdr);

}



PROG(IPV6OP)(struct __sk_buff *skb)

{

	struct ipv6_opt_hdr *ip6h, _ip6h;



	ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);

	if (!ip6h)

		return BPF_DROP;



	/* hlen is in 8-octets and does not include the first 8 bytes

	 * of the header

	 */

	skb->flow_keys->nhoff += (1 + ip6h->hdrlen) << 3;



	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 BPF_DROP;



	keys->nhoff += sizeof(*fragh);

	keys->is_frag = true;

	if (!(fragh->frag_off & bpf_htons(IP6_OFFSET)))

		keys->is_first_frag = true;



	return parse_ipv6_proto(skb, fragh->nexthdr);

}



PROG(MPLS)(struct __sk_buff *skb)

{

	struct mpls_label *mpls, _mpls;



	mpls = bpf_flow_dissect_get_header(skb, sizeof(*mpls), &_mpls);

	if (!mpls)

		return BPF_DROP;



	return BPF_OK;

}



PROG(VLAN)(struct __sk_buff *skb)

{

	struct bpf_flow_keys *keys = skb->flow_keys;

	struct vlan_hdr *vlan, _vlan;

	__be16 proto;



	/* Peek back to see if single or double-tagging */

	if (bpf_skb_load_bytes(skb, keys->nhoff - sizeof(proto), &proto,

			       sizeof(proto)))

		return BPF_DROP;



	/* Account for double-tagging */

	if (proto == bpf_htons(ETH_P_8021AD)) {

		vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);

		if (!vlan)

			return BPF_DROP;



		if (vlan->h_vlan_encapsulated_proto != bpf_htons(ETH_P_8021Q))

			return BPF_DROP;



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

	}



	vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);

	if (!vlan)

		return BPF_DROP;



	keys->nhoff += 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 BPF_DROP;



	return parse_eth_proto(skb, vlan->h_vlan_encapsulated_proto);

}



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