[PATCH RFC v4 net-next 20/26] samples: bpf: example of stateful socket filtering

[Alexei Starovoitov]

this socket filter example does:

- creates a hashtable in kernel with key 4 bytes and value 8 bytes

- populates map[6] = 0; map[17] = 0;  // 6 - tcp_proto, 17 - udp_proto

- loads eBPF program:
  r0 = skb[14 + 9]; // load one byte of ip->proto
  *(u32*)(fp - 4) = r0;
  value = bpf_map_lookup_elem(map_fd, fp - 4);
  if (value)
       (*(u64*)value) += 1;

- attaches this program to eth0 raw socket

- every second user space reads map[6] and map[17] to see how many
  TCP and UDP packets were seen on eth0

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
---
 samples/bpf/.gitignore     |    1 +
 samples/bpf/Makefile       |   12 ++++
 samples/bpf/sock_example.c |  158 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 171 insertions(+)
 create mode 100644 samples/bpf/.gitignore
 create mode 100644 samples/bpf/Makefile
 create mode 100644 samples/bpf/sock_example.c

diff --git a/samples/bpf/.gitignore b/samples/bpf/.gitignore
new file mode 100644
index 000000000000..5465c6e92a00
--- /dev/null
+++ b/samples/bpf/.gitignore
@@ -0,0 +1 @@
+sock_example
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
new file mode 100644
index 000000000000..63c65e5faf58
--- /dev/null
+++ b/samples/bpf/Makefile
@@ -0,0 +1,12 @@
+# kbuild trick to avoid linker error. Can be omitted if a module is built.
+obj- := dummy.o
+
+# List of programs to build
+hostprogs-y := sock_example
+
+sock_example-objs := sock_example.o libbpf.o
+
+# Tell kbuild to always build the programs
+always := $(hostprogs-y)
+
+HOSTCFLAGS += -I$(objtree)/usr/include
diff --git a/samples/bpf/sock_example.c b/samples/bpf/sock_example.c
new file mode 100644
index 000000000000..a577ee64de5b
--- /dev/null
+++ b/samples/bpf/sock_example.c
@@ -0,0 +1,158 @@
+/* eBPF example program:
+ * - creates a hashtable in kernel with key 4 bytes and value 8 bytes
+ *
+ * - populates map[6] = 0; map[17] = 0;  // 6 - tcp_proto, 17 - udp_proto
+ *
+ * - loads eBPF program:
+ *   r0 = skb[14 + 9]; // load one byte of ip->proto
+ *   *(u32*)(fp - 4) = r0;
+ *   value = bpf_map_lookup_elem(map_id, fp - 4);
+ *   if (value)
+ *        (*(u64*)value) += 1;
+ *
+ * - attaches this program to eth0 raw socket
+ *
+ * - every second user space reads map[6] and map[17] to see how many
+ *   TCP and UDP packets were seen on eth0
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <asm-generic/socket.h>
+#include <linux/netlink.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <linux/sockios.h>
+#include <linux/if_packet.h>
+#include <linux/bpf.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#include <linux/unistd.h>
+#include <string.h>
+#include <linux/filter.h>
+#include <stdlib.h>
+#include <arpa/inet.h>
+#include "libbpf.h"
+
+static int open_raw_sock(const char *name)
+{
+	struct sockaddr_ll sll;
+	struct packet_mreq mr;
+	struct ifreq ifr;
+	int sock;
+
+	sock = socket(PF_PACKET, SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC, htons(ETH_P_ALL));
+	if (sock < 0) {
+		printf("cannot open socket!\n");
+		return -1;
+	}
+
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy((char *)ifr.ifr_name, name, IFNAMSIZ);
+	if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0) {
+		printf("ioctl: %s\n", strerror(errno));
+		close(sock);
+		return -1;
+	}
+
+	memset(&sll, 0, sizeof(sll));
+	sll.sll_family = AF_PACKET;
+	sll.sll_ifindex = ifr.ifr_ifindex;
+	sll.sll_protocol = htons(ETH_P_ALL);
+	if (bind(sock, (struct sockaddr *)&sll, sizeof(sll)) < 0) {
+		printf("bind: %s\n", strerror(errno));
+		close(sock);
+		return -1;
+	}
+
+	memset(&mr, 0, sizeof(mr));
+	mr.mr_ifindex = ifr.ifr_ifindex;
+	mr.mr_type = PACKET_MR_PROMISC;
+	if (setsockopt(sock, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) < 0) {
+		printf("set_promisc: %s\n", strerror(errno));
+		close(sock);
+		return -1;
+	}
+	return sock;
+}
+
+static int test_sock(void)
+{
+	static struct bpf_insn prog[] = {
+		BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+		BPF_LD_ABS(BPF_B, 14 + 9 /* R0 = ip->proto */),
+		BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
+		BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+		BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
+		BPF_LD_MAP_FD(BPF_REG_1, 0),
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+		BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
+		BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+		BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
+		BPF_EXIT_INSN(),
+	};
+	int sock = -1, map_fd, prog_fd, i, key;
+	long long value = 0, tcp_cnt, udp_cnt;
+
+	map_fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value), 2);
+	if (map_fd < 0) {
+		printf("failed to create map '%s'\n", strerror(errno));
+		/* must have been left from previous aborted run, delete it */
+		goto cleanup;
+	}
+
+	key = 6; /* tcp */
+	if (bpf_update_elem(map_fd, &key, &value) < 0) {
+		printf("update err key=%d\n", key);
+		goto cleanup;
+	}
+
+	key = 17; /* udp */
+	if (bpf_update_elem(map_fd, &key, &value) < 0) {
+		printf("update err key=%d\n", key);
+		goto cleanup;
+	}
+
+	prog[5].imm = map_fd;
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog),
+				"GPL");
+	if (prog_fd < 0) {
+		printf("failed to load prog '%s'\n", strerror(errno));
+		goto cleanup;
+	}
+
+	sock = open_raw_sock("eth0");
+
+	if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER_EBPF, &prog_fd, sizeof(prog_fd)) < 0) {
+		printf("setsockopt %d\n", errno);
+		goto cleanup;
+	}
+
+	for (i = 0; i < 10; i++) {
+		key = 6;
+		if (bpf_lookup_elem(map_fd, &key, &tcp_cnt) < 0) {
+			printf("lookup err\n");
+			break;
+		}
+		key = 17;
+		if (bpf_lookup_elem(map_fd, &key, &udp_cnt) < 0) {
+			printf("lookup err\n");
+			break;
+		}
+		printf("TCP %lld UDP %lld packets\n", tcp_cnt, udp_cnt);
+		sleep(1);
+	}
+
+cleanup:
+	/* maps, programs, raw sockets will auto cleanup on process exit */
+
+	return 0;
+}
+
+int main(void)
+{
+	test_sock();
+	return 0;
+}
-- 
1.7.9.5

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