Merge branch 'libbpf: add netfilter link attach helper'

Florian Westphal says:

====================
v4: address comment from Daniel Xu:
  - use human-readable test names in 2/2

v3: address comments from Andrii:
  - prune verbose error message in 1/2
  - use bpf_link_create internally in 1/2
  - use subtests in patch 2/2

When initial netfilter bpf program type support got added one
suggestion was to extend libbpf with a helper to ease attachment
of nf programs to the hook locations.

Add such a helper and a demo test case that attaches a dummy
program to various combinations.

I tested that the selftest fails when changing the expected
outcome (i.e., set 'success' when it should fail and v.v.).
====================
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/lib/bpf/bpf.c

@@ -741,6 +741,14 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, tracing))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_NETFILTER:
+		attr.link_create.netfilter.pf = OPTS_GET(opts, netfilter.pf, 0);
+		attr.link_create.netfilter.hooknum = OPTS_GET(opts, netfilter.hooknum, 0);
+		attr.link_create.netfilter.priority = OPTS_GET(opts, netfilter.priority, 0);
+		attr.link_create.netfilter.flags = OPTS_GET(opts, netfilter.flags, 0);
+		if (!OPTS_ZEROED(opts, netfilter))
+			return libbpf_err(-EINVAL);
+		break;
 	default:
 		if (!OPTS_ZEROED(opts, flags))
 			return libbpf_err(-EINVAL);

tools/lib/bpf/bpf.h

@@ -349,6 +349,12 @@ struct bpf_link_create_opts {
 		struct {
 			__u64 cookie;
 		} tracing;
+		struct {
+			__u32 pf;
+			__u32 hooknum;
+			__s32 priority;
+			__u32 flags;
+		} netfilter;
 	};
 	size_t :0;
 };

tools/lib/bpf/libbpf.c

@@ -11815,6 +11815,48 @@ static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_l
 	return libbpf_get_error(*link);
 }
 
+struct bpf_link *bpf_program__attach_netfilter(const struct bpf_program *prog,
+					       const struct bpf_netfilter_opts *opts)
+{
+	LIBBPF_OPTS(bpf_link_create_opts, lopts);
+	struct bpf_link *link;
+	int prog_fd, link_fd;
+
+	if (!OPTS_VALID(opts, bpf_netfilter_opts))
+		return libbpf_err_ptr(-EINVAL);
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("prog '%s': can't attach before loaded\n", prog->name);
+		return libbpf_err_ptr(-EINVAL);
+	}
+
+	link = calloc(1, sizeof(*link));
+	if (!link)
+		return libbpf_err_ptr(-ENOMEM);
+
+	link->detach = &bpf_link__detach_fd;
+
+	lopts.netfilter.pf = OPTS_GET(opts, pf, 0);
+	lopts.netfilter.hooknum = OPTS_GET(opts, hooknum, 0);
+	lopts.netfilter.priority = OPTS_GET(opts, priority, 0);
+	lopts.netfilter.flags = OPTS_GET(opts, flags, 0);
+
+	link_fd = bpf_link_create(prog_fd, 0, BPF_NETFILTER, &lopts);
+	if (link_fd < 0) {
+		char errmsg[STRERR_BUFSIZE];
+
+		link_fd = -errno;
+		free(link);
+		pr_warn("prog '%s': failed to attach to netfilter: %s\n",
+			prog->name, libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
+		return libbpf_err_ptr(link_fd);
+	}
+	link->fd = link_fd;
+
+	return link;
+}
+
 struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
 {
 	struct bpf_link *link = NULL;

tools/lib/bpf/libbpf.h

@@ -718,6 +718,21 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_freplace(const struct bpf_program *prog,
 			     int target_fd, const char *attach_func_name);
 
+struct bpf_netfilter_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+
+	__u32 pf;
+	__u32 hooknum;
+	__s32 priority;
+	__u32 flags;
+};
+#define bpf_netfilter_opts__last_field flags
+
+LIBBPF_API struct bpf_link *
+bpf_program__attach_netfilter(const struct bpf_program *prog,
+			      const struct bpf_netfilter_opts *opts);
+
 struct bpf_map;
 
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);

tools/lib/bpf/libbpf.map

@@ -395,4 +395,5 @@ LIBBPF_1.2.0 {
 LIBBPF_1.3.0 {
 	global:
 		bpf_obj_pin_opts;
+		bpf_program__attach_netfilter;
 } LIBBPF_1.2.0;

tools/testing/selftests/bpf/prog_tests/netfilter_link_attach.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <netinet/in.h>
+#include <linux/netfilter.h>
+
+#include "test_progs.h"
+#include "test_netfilter_link_attach.skel.h"
+
+struct nf_link_test {
+	__u32 pf;
+	__u32 hooknum;
+	__s32 priority;
+	__u32 flags;
+
+	bool expect_success;
+	const char * const name;
+};
+
+static const struct nf_link_test nf_hook_link_tests[] = {
+	{ .name = "allzero", },
+	{ .pf = NFPROTO_NUMPROTO, .name = "invalid-pf", },
+	{ .pf = NFPROTO_IPV4, .hooknum = 42, .name = "invalid-hooknum", },
+	{ .pf = NFPROTO_IPV4, .priority = INT_MIN, .name = "invalid-priority-min", },
+	{ .pf = NFPROTO_IPV4, .priority = INT_MAX, .name = "invalid-priority-max", },
+	{ .pf = NFPROTO_IPV4, .flags = UINT_MAX, .name = "invalid-flags", },
+
+	{ .pf = NFPROTO_INET, .priority = 1, .name = "invalid-inet-not-supported", },
+
+	{ .pf = NFPROTO_IPV4, .priority = -10000, .expect_success = true, .name = "attach ipv4", },
+	{ .pf = NFPROTO_IPV6, .priority =  10001, .expect_success = true, .name = "attach ipv6", },
+};
+
+void test_netfilter_link_attach(void)
+{
+	struct test_netfilter_link_attach *skel;
+	struct bpf_program *prog;
+	LIBBPF_OPTS(bpf_netfilter_opts, opts);
+	int i;
+
+	skel = test_netfilter_link_attach__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_netfilter_link_attach__open_and_load"))
+		goto out;
+
+	prog = skel->progs.nf_link_attach_test;
+	if (!ASSERT_OK_PTR(prog, "attach program"))
+		goto out;
+
+	for (i = 0; i < ARRAY_SIZE(nf_hook_link_tests); i++) {
+		struct bpf_link *link;
+
+		if (!test__start_subtest(nf_hook_link_tests[i].name))
+			continue;
+
+#define X(opts, m, i)	opts.m = nf_hook_link_tests[(i)].m
+		X(opts, pf, i);
+		X(opts, hooknum, i);
+		X(opts, priority, i);
+		X(opts, flags, i);
+#undef X
+		link = bpf_program__attach_netfilter(prog, &opts);
+		if (nf_hook_link_tests[i].expect_success) {
+			struct bpf_link *link2;
+
+			if (!ASSERT_OK_PTR(link, "program attach successful"))
+				continue;
+
+			link2 = bpf_program__attach_netfilter(prog, &opts);
+			ASSERT_ERR_PTR(link2, "attach program with same pf/hook/priority");
+
+			if (!ASSERT_OK(bpf_link__destroy(link), "link destroy"))
+				break;
+
+			link2 = bpf_program__attach_netfilter(prog, &opts);
+			if (!ASSERT_OK_PTR(link2, "program reattach successful"))
+				continue;
+			if (!ASSERT_OK(bpf_link__destroy(link2), "link destroy"))
+				break;
+		} else {
+			ASSERT_ERR_PTR(link, "program load failure");
+		}
+	}
+
+out:
+	test_netfilter_link_attach__destroy(skel);
+}
+

tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+#define NF_ACCEPT 1
+
+SEC("netfilter")
+int nf_link_attach_test(struct bpf_nf_ctx *ctx)
+{
+	return NF_ACCEPT;
+}
+
+char _license[] SEC("license") = "GPL";