[PATCH bpf-next v4 2/2] selftests/bpf: Cover attach type checks in link update

[Sanghyun Park <sanghyun.park.cnu@gmail.com>]

Add regression coverage for link update compatibility. Verify that a UDP6
sock_addr program cannot replace a UDP4 program and that an LSM_MAC
program cannot replace an LSM_CGROUP program.

Also verify that CGROUP_SKB attachment still requires CAP_NET_ADMIN, while
an existing link can be updated after dropping CAP_NET_ADMIN and
CAP_SYS_ADMIN.

Signed-off-by: Sanghyun Park <sanghyun.park.cnu@gmail.com>
---
 .../selftests/bpf/prog_tests/cgroup_link.c    | 51 +++++++++++++++++++
 .../selftests/bpf/prog_tests/lsm_cgroup.c     | 10 ++++
 .../testing/selftests/bpf/progs/lsm_cgroup.c  |  6 +++
 .../selftests/bpf/progs/test_cgroup_link.c    | 14 ++++-
 4 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_link.c b/tools/testing/selftests/bpf/prog_tests/cgroup_link.c
index 15093a69510e..b3219314596e 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_link.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_link.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <test_progs.h>
+#include "cap_helpers.h"
 #include "cgroup_helpers.h"
 #include "testing_helpers.h"
 #include "test_cgroup_link.skel.h"
@@ -24,6 +25,55 @@ int ping_and_check(int exp_calls, int exp_alt_calls)
 	return 0;
 }
 
+static void test_cgroup_link_update(int cg_fd)
+{
+	const __u64 caps = (1ULL << CAP_NET_ADMIN) | (1ULL << CAP_SYS_ADMIN);
+	struct bpf_link *link = NULL;
+	__u64 saved_caps = 0;
+	int err;
+
+	link = bpf_program__attach_cgroup(skel->progs.sendmsg4, cg_fd);
+	if (!ASSERT_OK_PTR(link, "attach_sendmsg4"))
+		goto cleanup;
+
+	err = bpf_link__update_program(link, skel->progs.sendmsg6);
+	ASSERT_EQ(err, -EINVAL, "reject_sendmsg6_update");
+	bpf_link__destroy(link);
+	link = NULL;
+
+	err = cap_disable_effective(caps, &saved_caps);
+	if (!ASSERT_OK(err, "drop_caps_for_attach"))
+		goto cleanup;
+
+	link = bpf_program__attach_cgroup(skel->progs.egress, cg_fd);
+	if (!ASSERT_ERR_PTR(link, "attach_without_net_admin"))
+		goto cleanup;
+	err = libbpf_get_error(link);
+	link = NULL;
+	if (!ASSERT_EQ(err, -EPERM, "attach_err"))
+		goto cleanup;
+
+	err = cap_enable_effective(saved_caps & caps, NULL);
+	if (!ASSERT_OK(err, "restore_caps_for_attach"))
+		goto cleanup;
+
+	link = bpf_program__attach_cgroup(skel->progs.egress, cg_fd);
+	if (!ASSERT_OK_PTR(link, "attach_egress"))
+		goto cleanup;
+
+	err = cap_disable_effective(caps, &saved_caps);
+	if (!ASSERT_OK(err, "drop_caps"))
+		goto cleanup;
+
+	err = bpf_link__update_program(link, skel->progs.egress_alt);
+	ASSERT_OK(err, "update_without_net_admin");
+
+cleanup:
+	err = cap_enable_effective(saved_caps & caps, NULL);
+	ASSERT_OK(err, "restore_caps");
+	bpf_link__destroy(link);
+}
+
 void serial_test_cgroup_link(void)
 {
 	struct {
@@ -61,6 +111,7 @@ void serial_test_cgroup_link(void)
 	err = join_cgroup(cgs[last_cg].path);
 	if (CHECK(err, "cg_join", "fail: %d\n", err))
 		goto cleanup;
+	test_cgroup_link_update(cgs[last_cg].fd);
 
 	for (i = 0; i < cg_nr; i++) {
 		links[i] = bpf_program__attach_cgroup(skel->progs.egress,
diff --git a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
index 41e867467f6c..85b0af4f486a 100644
--- a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
+++ b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
@@ -74,6 +74,7 @@ static void test_lsm_cgroup_functional(void)
 	int bind_prog_fd = -1;
 	int bind_link_fd = -1;
 	int clone_prog_fd = -1;
+	int mac_prog_fd;
 	int err, fd, prio;
 	socklen_t socklen;
 
@@ -156,6 +157,15 @@ static void test_lsm_cgroup_functional(void)
 	ASSERT_EQ(query_prog_cnt(cgroup_fd, "bpf_lsm_socket_bind"), 1, "prog count");
 	ASSERT_EQ(query_prog_cnt(cgroup_fd, NULL), 4, "total prog count");
 
+	fd = bpf_link_create(bpf_program__fd(skel->progs.socket_first),
+			     cgroup_fd, BPF_LSM_CGROUP, NULL);
+	if (!ASSERT_GE(fd, 0, "link create socket_first"))
+		goto detach_cgroup;
+	mac_prog_fd = bpf_program__fd(skel->progs.socket_create_lsm);
+	err = bpf_link_update(fd, mac_prog_fd, NULL);
+	ASSERT_EQ(err, -EINVAL, "reject lsm_mac link update");
+	close(fd);
+
 	/* Attach another instance of bind program to another cgroup.
 	 * This should trigger the reuse of the trampoline shim (two
 	 * programs attaching to the same btf_id).
diff --git a/tools/testing/selftests/bpf/progs/lsm_cgroup.c b/tools/testing/selftests/bpf/progs/lsm_cgroup.c
index 3bfa479104be..30727945cecc 100644
--- a/tools/testing/selftests/bpf/progs/lsm_cgroup.c
+++ b/tools/testing/selftests/bpf/progs/lsm_cgroup.c
@@ -213,6 +213,12 @@ int BPF_PROG(socket_first, int family, int type, int protocol, int kern)
 	return 0;
 }
 
+SEC("lsm/socket_create")
+int BPF_PROG(socket_create_lsm, int family, int type, int protocol, int kern)
+{
+	return 0;
+}
+
 SEC("lsm_cgroup/socket_create")
 int BPF_PROG(socket_second, int family, int type, int protocol, int kern)
 {
diff --git a/tools/testing/selftests/bpf/progs/test_cgroup_link.c b/tools/testing/selftests/bpf/progs/test_cgroup_link.c
index 4faba88e45a5..a987744d129c 100644
--- a/tools/testing/selftests/bpf/progs/test_cgroup_link.c
+++ b/tools/testing/selftests/bpf/progs/test_cgroup_link.c
@@ -20,5 +20,17 @@ int egress_alt(struct __sk_buff *skb)
 	return 1;
 }
 
-char _license[] SEC("license") = "GPL";
+SEC("cgroup/sendmsg4")
+int sendmsg4(struct bpf_sock_addr *ctx)
+{
+	return 1;
+}
 
+SEC("cgroup/sendmsg6")
+int sendmsg6(struct bpf_sock_addr *ctx)
+{
+	ctx->msg_src_ip6[2] = 0;
+	return 1;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.48.1