samples: bpf: Refactor test_cgrp2_sock2 program with libbpf

This commit refactors the existing cgroup program with libbpf bpf
loader. The original test_cgrp2_sock2 has keeped the bpf program
attached to the cgroup hierarchy even after the exit of user program.
To implement the same functionality with libbpf, this commit uses the
BPF_LINK_PINNING to pin the link attachment even after it is closed.

Since this uses LINK instead of ATTACH, detach of bpf program from
cgroup with 'test_cgrp2_sock' is not used anymore.

The code to mount the bpf was added to the .sh file in case the bpff
was not mounted on /sys/fs/bpf. Additionally, to fix the problem that
shell script cannot find the binary object from the current path,
relative path './' has been added in front of binary.

Fixes: 554ae6e7 ("samples/bpf: add userspace example for prohibiting sockets")
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201124090310.24374-3-danieltimlee@gmail.com

samples/bpf/Makefile

@@ -82,7 +82,7 @@ test_overhead-objs := bpf_load.o test_overhead_user.o
 test_cgrp2_array_pin-objs := test_cgrp2_array_pin.o
 test_cgrp2_attach-objs := test_cgrp2_attach.o
 test_cgrp2_sock-objs := test_cgrp2_sock.o
-test_cgrp2_sock2-objs := bpf_load.o test_cgrp2_sock2.o
+test_cgrp2_sock2-objs := test_cgrp2_sock2.o
 xdp1-objs := xdp1_user.o
 # reuse xdp1 source intentionally
 xdp2-objs := xdp1_user.o

samples/bpf/test_cgrp2_sock2.c

@@ -20,9 +20,9 @@
 #include <net/if.h>
 #include <linux/bpf.h>
 #include <bpf/bpf.h>
+#include <bpf/libbpf.h>
 
 #include "bpf_insn.h"
-#include "bpf_load.h"
 
 static int usage(const char *argv0)
 {
@@ -32,37 +32,64 @@ static int usage(const char *argv0)
 
 int main(int argc, char **argv)
 {
-	int cg_fd, ret, filter_id = 0;
+	int cg_fd, err, ret = EXIT_FAILURE, filter_id = 0, prog_cnt = 0;
+	const char *link_pin_path = "/sys/fs/bpf/test_cgrp2_sock2";
+	struct bpf_link *link = NULL;
+	struct bpf_program *progs[2];
+	struct bpf_program *prog;
+	struct bpf_object *obj;
 
 	if (argc < 3)
 		return usage(argv[0]);
 
+	if (argc > 3)
+		filter_id = atoi(argv[3]);
+
 	cg_fd = open(argv[1], O_DIRECTORY | O_RDONLY);
 	if (cg_fd < 0) {
 		printf("Failed to open cgroup path: '%s'\n", strerror(errno));
-		return EXIT_FAILURE;
+		return ret;
 	}
 
-	if (load_bpf_file(argv[2]))
-		return EXIT_FAILURE;
-
-	printf("Output from kernel verifier:\n%s\n-------\n", bpf_log_buf);
+	obj = bpf_object__open_file(argv[2], NULL);
+	if (libbpf_get_error(obj)) {
+		printf("ERROR: opening BPF object file failed\n");
+		return ret;
+	}
 
-	if (argc > 3)
-		filter_id = atoi(argv[3]);
+	bpf_object__for_each_program(prog, obj) {
+		progs[prog_cnt] = prog;
+		prog_cnt++;
+	}
 
 	if (filter_id >= prog_cnt) {
 		printf("Invalid program id; program not found in file\n");
-		return EXIT_FAILURE;
+		goto cleanup;
+	}
+
+	/* load BPF program */
+	if (bpf_object__load(obj)) {
+		printf("ERROR: loading BPF object file failed\n");
+		goto cleanup;
 	}
 
-	ret = bpf_prog_attach(prog_fd[filter_id], cg_fd,
-			      BPF_CGROUP_INET_SOCK_CREATE, 0);
-	if (ret < 0) {
-		printf("Failed to attach prog to cgroup: '%s'\n",
-		       strerror(errno));
-		return EXIT_FAILURE;
+	link = bpf_program__attach_cgroup(progs[filter_id], cg_fd);
+	if (libbpf_get_error(link)) {
+		printf("ERROR: bpf_program__attach failed\n");
+		link = NULL;
+		goto cleanup;
 	}
 
-	return EXIT_SUCCESS;
+	err = bpf_link__pin(link, link_pin_path);
+	if (err < 0) {
+		printf("ERROR: bpf_link__pin failed: %d\n", err);
+		goto cleanup;
+	}
+
+	ret = EXIT_SUCCESS;
+
+cleanup:
+	bpf_link__destroy(link);
+	bpf_object__close(obj);
+	return ret;
 }

samples/bpf/test_cgrp2_sock2.sh

 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0
 
+BPFFS=/sys/fs/bpf
+LINK_PIN=$BPFFS/test_cgrp2_sock2
+
 function config_device {
 	ip netns add at_ns0
 	ip link add veth0 type veth peer name veth0b
@@ -21,16 +24,22 @@ function config_cgroup {
 	echo $$ >> /tmp/cgroupv2/foo/cgroup.procs
 }
 
+function config_bpffs {
+	if mount | grep $BPFFS > /dev/null; then
+		echo "bpffs already mounted"
+	else
+		echo "bpffs not mounted. Mounting..."
+		mount -t bpf none $BPFFS
+	fi
+}
 
 function attach_bpf {
-	test_cgrp2_sock2 /tmp/cgroupv2/foo sock_flags_kern.o $1
+	./test_cgrp2_sock2 /tmp/cgroupv2/foo sock_flags_kern.o $1
 	[ $? -ne 0 ] && exit 1
 }
 
 function cleanup {
-	if [ -d /tmp/cgroupv2/foo ]; then
-		test_cgrp2_sock -d /tmp/cgroupv2/foo
-	fi
+	rm -rf $LINK_PIN
 	ip link del veth0b
 	ip netns delete at_ns0
 	umount /tmp/cgroupv2
@@ -42,6 +51,7 @@ cleanup 2>/dev/null
 set -e
 config_device
 config_cgroup
+config_bpffs
 set +e
 
 #
@@ -62,6 +72,9 @@ if [ $? -eq 0 ]; then
 	exit 1
 fi
 
+rm -rf $LINK_PIN
+sleep 1                 # Wait for link detach
+
 #
 # Test 2 - fail ping
 #