On 2026/8/31 10:39, Sanghyun Park wrote:
> 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 <[email protected]>
> ---
> .../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);
imo, it is not a good idea to embed test_cgroup_link_update() here.
Better to add it as a subtest with its own env setup/cleanup:
static void test_cgroup_link_attach(void)
{
/* previous serial_test_cgroup_link() function body */
}
static void test_cgroup_link_update(void)
{
/* setup its own skel and cg env */
/* test link_update */
/* cleanup the skel and cg env */
}
void serial_test_cgroup_link(void)
{
if (test__start_subtest("attach"))
test_cgroup_link_attach();
if (test__start_subtest("update"))
test_cgroup_link_update();
}
>
> 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);
Rewrite to bpf_link_update(fd,
bpf_program__fd(skel->progs.socket_create_lsm), NULL).
Then, the 'mac_prog_fd' can be dropped.
Thanks,
Leon
> + ASSERT_EQ(err, -EINVAL, "reject lsm_mac link update");> +
> close(fd);
> [...]
