samples: bpf: example of stateful socket filtering

this socket filter example does:
- creates arraymap in kernel with key 4 bytes and value 8 bytes

- loads eBPF program which assumes that packet is IPv4 and loads one byte of
  IP->proto from the packet and uses it as a key in a map

  r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
  *(u32*)(fp - 4) = r0;
  value = bpf_map_lookup_elem(map_fd, fp - 4);
  if (value)
       (*(u64*)value) += 1;

- attaches this program to raw socket

- every second user space reads map[IPPROTO_TCP], map[IPPROTO_UDP], map[IPPROTO_ICMP]
  to see how many packets of given protocol were seen on loopback interface

Usage:
$sudo samples/bpf/sock_example
TCP 0 UDP 0 ICMP 0 packets
TCP 187600 UDP 0 ICMP 4 packets
TCP 376504 UDP 0 ICMP 8 packets
TCP 563116 UDP 0 ICMP 12 packets
TCP 753144 UDP 0 ICMP 16 packets

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 0 deletions

diff --git a/samples/bpf/libbpf.c b/samples/bpf/libbpf.c
index 17bb520eb57f..46d50b7ddf79 100644
--- a/samples/bpf/libbpf.c
+++ b/samples/bpf/libbpf.c
@@ -7,6 +7,10 @@
 #include <linux/netlink.h>
 #include <linux/bpf.h>
 #include <errno.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <linux/if_packet.h>
+#include <arpa/inet.h>
 #include "libbpf.h"
 
 static __u64 ptr_to_u64(void *ptr)
@@ -93,3 +97,27 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
 
 	return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
 }
+
+int open_raw_sock(const char *name)
+{
+	struct sockaddr_ll sll;
+	int sock;
+
+	sock = socket(PF_PACKET, SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC, htons(ETH_P_ALL));
+	if (sock < 0) {
+		printf("cannot create raw socket\n");
+		return -1;
+	}
+
+	memset(&sll, 0, sizeof(sll));
+	sll.sll_family = AF_PACKET;
+	sll.sll_ifindex = if_nametoindex(name);
+	sll.sll_protocol = htons(ETH_P_ALL);
+	if (bind(sock, (struct sockaddr *)&sll, sizeof(sll)) < 0) {
+		printf("bind to %s: %s\n", name, strerror(errno));
+		close(sock);
+		return -1;
+	}
+
+	return sock;
+}