KFunc bpf_dynptr_from_skb
Get dynptrs whose underlying pointer points to a skb.
Definition
For bpf prog types that don't support writes on skb data, the dynptr is read-only (bpf_dynptr_write() will return an error)
For reads and writes through the bpf_dynptr_read() and bpf_dynptr_write() interfaces, reading and writing from/to data in the head as well as from/to non-linear paged buffers is supported. Data slices through the bpf_dynptr_data API are not supported; instead bpf_dynptr_slice() and bpf_dynptr_slice_rdwr() should be used.
int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags, struct bpf_dynptr_kern *ptr__uninit)
Usage
The dynptr acts on skb data. skb dynptrs have two main benefits. One is that they allow operations on sizes that are not statically known at compile-time (eg variable-sized accesses). Another is that parsing the packet data through dynptrs (instead of through direct access of skb->data and skb->data_end) can be more ergonomic and less brittle (eg does not need manual if checking for being within bounds of data_end).
Program types
The following program types can make use of this kfunc:
- BPF_PROG_TYPE_CGROUP_SKB
- BPF_PROG_TYPE_LWT_IN
- BPF_PROG_TYPE_LWT_OUT
- BPF_PROG_TYPE_LWT_SEG6LOCAL
- BPF_PROG_TYPE_LWT_XMIT
- BPF_PROG_TYPE_NETFILTER
- BPF_PROG_TYPE_SCHED_ACT
- BPF_PROG_TYPE_SCHED_CLS
- BPF_PROG_TYPE_SK_SKB
- BPF_PROG_TYPE_SOCKET_FILTER
Example
L4LB noinline dynptr
// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2017 Facebook
#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/ip.h>
#include <linux/ipv6.h>
#include <linux/icmp.h>
#include <linux/icmpv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <bpf/bpf_helpers.h>
#include "test_iptunnel_common.h"
#include <bpf/bpf_endian.h>
#include "bpf_kfuncs.h"
static __always_inline __u32 rol32(__u32 word, unsigned int shift)
{
return (word << shift) | (word >> ((-shift) & 31));
}
/* copy paste of jhash from kernel sources to make sure llvm
* can compile it into valid sequence of bpf instructions
*/
#define __jhash_mix(a, b, c) \
{ \
a -= c; a ^= rol32(c, 4); c += b; \
b -= a; b ^= rol32(a, 6); a += c; \
c -= b; c ^= rol32(b, 8); b += a; \
a -= c; a ^= rol32(c, 16); c += b; \
b -= a; b ^= rol32(a, 19); a += c; \
c -= b; c ^= rol32(b, 4); b += a; \
}
#define __jhash_final(a, b, c) \
{ \
c ^= b; c -= rol32(b, 14); \
a ^= c; a -= rol32(c, 11); \
b ^= a; b -= rol32(a, 25); \
c ^= b; c -= rol32(b, 16); \
a ^= c; a -= rol32(c, 4); \
b ^= a; b -= rol32(a, 14); \
c ^= b; c -= rol32(b, 24); \
}
#define JHASH_INITVAL 0xdeadbeef
typedef unsigned int u32;
static __noinline u32 jhash(const void *key, u32 length, u32 initval)
{
u32 a, b, c;
const unsigned char *k = key;
a = b = c = JHASH_INITVAL + length + initval;
while (length > 12) {
a += *(u32 *)(k);
b += *(u32 *)(k + 4);
c += *(u32 *)(k + 8);
__jhash_mix(a, b, c);
length -= 12;
k += 12;
}
switch (length) {
case 12: c += (u32)k[11]<<24;
case 11: c += (u32)k[10]<<16;
case 10: c += (u32)k[9]<<8;
case 9: c += k[8];
case 8: b += (u32)k[7]<<24;
case 7: b += (u32)k[6]<<16;
case 6: b += (u32)k[5]<<8;
case 5: b += k[4];
case 4: a += (u32)k[3]<<24;
case 3: a += (u32)k[2]<<16;
case 2: a += (u32)k[1]<<8;
case 1: a += k[0];
__jhash_final(a, b, c);
case 0: /* Nothing left to add */
break;
}
return c;
}
static __noinline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
{
a += initval;
b += initval;
c += initval;
__jhash_final(a, b, c);
return c;
}
static __noinline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
}
#define PCKT_FRAGMENTED 65343
#define IPV4_HDR_LEN_NO_OPT 20
#define IPV4_PLUS_ICMP_HDR 28
#define IPV6_PLUS_ICMP_HDR 48
#define RING_SIZE 2
#define MAX_VIPS 12
#define MAX_REALS 5
#define CTL_MAP_SIZE 16
#define CH_RINGS_SIZE (MAX_VIPS * RING_SIZE)
#define F_IPV6 (1 << 0)
#define F_HASH_NO_SRC_PORT (1 << 0)
#define F_ICMP (1 << 0)
#define F_SYN_SET (1 << 1)
struct packet_description {
union {
__be32 src;
__be32 srcv6[4];
};
union {
__be32 dst;
__be32 dstv6[4];
};
union {
__u32 ports;
__u16 port16[2];
};
__u8 proto;
__u8 flags;
};
struct ctl_value {
union {
__u64 value;
__u32 ifindex;
__u8 mac[6];
};
};
struct vip_meta {
__u32 flags;
__u32 vip_num;
};
struct real_definition {
union {
__be32 dst;
__be32 dstv6[4];
};
__u8 flags;
};
struct vip_stats {
__u64 bytes;
__u64 pkts;
};
struct eth_hdr {
unsigned char eth_dest[ETH_ALEN];
unsigned char eth_source[ETH_ALEN];
unsigned short eth_proto;
};
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, MAX_VIPS);
__type(key, struct vip);
__type(value, struct vip_meta);
} vip_map SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, CH_RINGS_SIZE);
__type(key, __u32);
__type(value, __u32);
} ch_rings SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, MAX_REALS);
__type(key, __u32);
__type(value, struct real_definition);
} reals SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
__uint(max_entries, MAX_VIPS);
__type(key, __u32);
__type(value, struct vip_stats);
} stats SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, CTL_MAP_SIZE);
__type(key, __u32);
__type(value, struct ctl_value);
} ctl_array SEC(".maps");
static __noinline __u32 get_packet_hash(struct packet_description *pckt, bool ipv6)
{
if (ipv6)
return jhash_2words(jhash(pckt->srcv6, 16, MAX_VIPS),
pckt->ports, CH_RINGS_SIZE);
else
return jhash_2words(pckt->src, pckt->ports, CH_RINGS_SIZE);
}
static __noinline bool get_packet_dst(struct real_definition **real,
struct packet_description *pckt,
struct vip_meta *vip_info,
bool is_ipv6)
{
__u32 hash = get_packet_hash(pckt, is_ipv6);
__u32 key = RING_SIZE * vip_info->vip_num + hash % RING_SIZE;
__u32 *real_pos;
if (hash != 0x358459b7 /* jhash of ipv4 packet */ &&
hash != 0x2f4bc6bb /* jhash of ipv6 packet */)
return false;
real_pos = bpf_map_lookup_elem(&ch_rings, &key);
if (!real_pos)
return false;
key = *real_pos;
*real = bpf_map_lookup_elem(&reals, &key);
if (!(*real))
return false;
return true;
}
static __noinline int parse_icmpv6(struct bpf_dynptr *skb_ptr, __u64 off,
struct packet_description *pckt)
{
__u8 buffer[sizeof(struct ipv6hdr)] = {};
struct icmp6hdr *icmp_hdr;
struct ipv6hdr *ip6h;
icmp_hdr = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!icmp_hdr)
return TC_ACT_SHOT;
if (icmp_hdr->icmp6_type != ICMPV6_PKT_TOOBIG)
return TC_ACT_OK;
off += sizeof(struct icmp6hdr);
ip6h = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!ip6h)
return TC_ACT_SHOT;
pckt->proto = ip6h->nexthdr;
pckt->flags |= F_ICMP;
memcpy(pckt->srcv6, ip6h->daddr.s6_addr32, 16);
memcpy(pckt->dstv6, ip6h->saddr.s6_addr32, 16);
return TC_ACT_UNSPEC;
}
static __noinline int parse_icmp(struct bpf_dynptr *skb_ptr, __u64 off,
struct packet_description *pckt)
{
__u8 buffer_icmp[sizeof(struct iphdr)] = {};
__u8 buffer_ip[sizeof(struct iphdr)] = {};
struct icmphdr *icmp_hdr;
struct iphdr *iph;
icmp_hdr = bpf_dynptr_slice(skb_ptr, off, buffer_icmp, sizeof(buffer_icmp));
if (!icmp_hdr)
return TC_ACT_SHOT;
if (icmp_hdr->type != ICMP_DEST_UNREACH ||
icmp_hdr->code != ICMP_FRAG_NEEDED)
return TC_ACT_OK;
off += sizeof(struct icmphdr);
iph = bpf_dynptr_slice(skb_ptr, off, buffer_ip, sizeof(buffer_ip));
if (!iph || iph->ihl != 5)
return TC_ACT_SHOT;
pckt->proto = iph->protocol;
pckt->flags |= F_ICMP;
pckt->src = iph->daddr;
pckt->dst = iph->saddr;
return TC_ACT_UNSPEC;
}
static __noinline bool parse_udp(struct bpf_dynptr *skb_ptr, __u64 off,
struct packet_description *pckt)
{
__u8 buffer[sizeof(struct udphdr)] = {};
struct udphdr *udp;
udp = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!udp)
return false;
if (!(pckt->flags & F_ICMP)) {
pckt->port16[0] = udp->source;
pckt->port16[1] = udp->dest;
} else {
pckt->port16[0] = udp->dest;
pckt->port16[1] = udp->source;
}
return true;
}
static __noinline bool parse_tcp(struct bpf_dynptr *skb_ptr, __u64 off,
struct packet_description *pckt)
{
__u8 buffer[sizeof(struct tcphdr)] = {};
struct tcphdr *tcp;
tcp = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!tcp)
return false;
if (tcp->syn)
pckt->flags |= F_SYN_SET;
if (!(pckt->flags & F_ICMP)) {
pckt->port16[0] = tcp->source;
pckt->port16[1] = tcp->dest;
} else {
pckt->port16[0] = tcp->dest;
pckt->port16[1] = tcp->source;
}
return true;
}
static __noinline int process_packet(struct bpf_dynptr *skb_ptr,
struct eth_hdr *eth, __u64 off,
bool is_ipv6, struct __sk_buff *skb)
{
struct packet_description pckt = {};
struct bpf_tunnel_key tkey = {};
struct vip_stats *data_stats;
struct real_definition *dst;
struct vip_meta *vip_info;
struct ctl_value *cval;
__u32 v4_intf_pos = 1;
__u32 v6_intf_pos = 2;
struct ipv6hdr *ip6h;
struct vip vip = {};
struct iphdr *iph;
int tun_flag = 0;
__u16 pkt_bytes;
__u64 iph_len;
__u32 ifindex;
__u8 protocol;
__u32 vip_num;
int action;
tkey.tunnel_ttl = 64;
if (is_ipv6) {
__u8 buffer[sizeof(struct ipv6hdr)] = {};
ip6h = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!ip6h)
return TC_ACT_SHOT;
iph_len = sizeof(struct ipv6hdr);
protocol = ip6h->nexthdr;
pckt.proto = protocol;
pkt_bytes = bpf_ntohs(ip6h->payload_len);
off += iph_len;
if (protocol == IPPROTO_FRAGMENT) {
return TC_ACT_SHOT;
} else if (protocol == IPPROTO_ICMPV6) {
action = parse_icmpv6(skb_ptr, off, &pckt);
if (action >= 0)
return action;
off += IPV6_PLUS_ICMP_HDR;
} else {
memcpy(pckt.srcv6, ip6h->saddr.s6_addr32, 16);
memcpy(pckt.dstv6, ip6h->daddr.s6_addr32, 16);
}
} else {
__u8 buffer[sizeof(struct iphdr)] = {};
iph = bpf_dynptr_slice(skb_ptr, off, buffer, sizeof(buffer));
if (!iph || iph->ihl != 5)
return TC_ACT_SHOT;
protocol = iph->protocol;
pckt.proto = protocol;
pkt_bytes = bpf_ntohs(iph->tot_len);
off += IPV4_HDR_LEN_NO_OPT;
if (iph->frag_off & PCKT_FRAGMENTED)
return TC_ACT_SHOT;
if (protocol == IPPROTO_ICMP) {
action = parse_icmp(skb_ptr, off, &pckt);
if (action >= 0)
return action;
off += IPV4_PLUS_ICMP_HDR;
} else {
pckt.src = iph->saddr;
pckt.dst = iph->daddr;
}
}
protocol = pckt.proto;
if (protocol == IPPROTO_TCP) {
if (!parse_tcp(skb_ptr, off, &pckt))
return TC_ACT_SHOT;
} else if (protocol == IPPROTO_UDP) {
if (!parse_udp(skb_ptr, off, &pckt))
return TC_ACT_SHOT;
} else {
return TC_ACT_SHOT;
}
if (is_ipv6)
memcpy(vip.daddr.v6, pckt.dstv6, 16);
else
vip.daddr.v4 = pckt.dst;
vip.dport = pckt.port16[1];
vip.protocol = pckt.proto;
vip_info = bpf_map_lookup_elem(&vip_map, &vip);
if (!vip_info) {
vip.dport = 0;
vip_info = bpf_map_lookup_elem(&vip_map, &vip);
if (!vip_info)
return TC_ACT_SHOT;
pckt.port16[1] = 0;
}
if (vip_info->flags & F_HASH_NO_SRC_PORT)
pckt.port16[0] = 0;
if (!get_packet_dst(&dst, &pckt, vip_info, is_ipv6))
return TC_ACT_SHOT;
if (dst->flags & F_IPV6) {
cval = bpf_map_lookup_elem(&ctl_array, &v6_intf_pos);
if (!cval)
return TC_ACT_SHOT;
ifindex = cval->ifindex;
memcpy(tkey.remote_ipv6, dst->dstv6, 16);
tun_flag = BPF_F_TUNINFO_IPV6;
} else {
cval = bpf_map_lookup_elem(&ctl_array, &v4_intf_pos);
if (!cval)
return TC_ACT_SHOT;
ifindex = cval->ifindex;
tkey.remote_ipv4 = dst->dst;
}
vip_num = vip_info->vip_num;
data_stats = bpf_map_lookup_elem(&stats, &vip_num);
if (!data_stats)
return TC_ACT_SHOT;
data_stats->pkts++;
data_stats->bytes += pkt_bytes;
bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), tun_flag);
*(u32 *)eth->eth_dest = tkey.remote_ipv4;
return bpf_redirect(ifindex, 0);
}
SEC("tc")
int balancer_ingress(struct __sk_buff *ctx)
{
__u8 buffer[sizeof(struct eth_hdr)] = {};
struct bpf_dynptr ptr;
struct eth_hdr *eth;
__u32 eth_proto;
__u32 nh_off;
int err;
nh_off = sizeof(struct eth_hdr);
bpf_dynptr_from_skb(ctx, 0, &ptr);
eth = bpf_dynptr_slice_rdwr(&ptr, 0, buffer, sizeof(buffer));
if (!eth)
return TC_ACT_SHOT;
eth_proto = eth->eth_proto;
if (eth_proto == bpf_htons(ETH_P_IP))
err = process_packet(&ptr, eth, nh_off, false, ctx);
else if (eth_proto == bpf_htons(ETH_P_IPV6))
err = process_packet(&ptr, eth, nh_off, true, ctx);
else
return TC_ACT_SHOT;
if (eth == buffer)
bpf_dynptr_write(&ptr, 0, buffer, sizeof(buffer), 0);
return err;
}
char _license[] SEC("license") = "GPL";