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selftests/bpf: Test cgroup link replace with BPF_F_PREORDER

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Add a cgroup_preorder case that attaches a normal and a BPF_F_PREORDER
program to a cgroup (effective order [2, 1]), then replaces the normal
link's program via bpf_link_update() and checks the effective order
becomes [2, 3] — i.e. only the non-preorder slot changes. Without the
replace_effective_prog() fix the array is corrupted and the order is
wrong.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260619063520.2690547-3-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Amery Hung 2026-06-18 23:35:20 -07:00 committed by Alexei Starovoitov
parent f08aaee315
commit a6ff26f360
1 changed files with 77 additions and 0 deletions
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77
tools/testing/selftests/bpf/prog_tests/cgroup_preorder.c
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@ -102,6 +102,82 @@ static int run_getsockopt_test(int cg_parent, int cg_child, int sock_fd, bool al
return err;
}
/*
* Replacing a link's program (bpf_link_update) must target the correct slot in
* the effective array even when a BPF_F_PREORDER program is attached to the
* same cgroup. All programs here are attached to a single cgroup; "parent" is
* reused only as a third distinct program.
*
* Attach child(1) normally and child_2(2) with BPF_F_PREORDER, so the effective
* order is [2, 1]. Then replace child(1)'s program with parent(3): only the
* non-preorder slot changes, giving [2, 3].
*/
static int run_link_replace_test(int cgroup_fd, int sock_fd)
{
LIBBPF_OPTS(bpf_link_create_opts, create_opts);
int err = 0, normal_link = -1, preorder_link = -1;
struct cgroup_preorder *skel = NULL;
enum bpf_attach_type atype;
__u8 *result, buf = 0x00;
socklen_t optlen = 1;
skel = cgroup_preorder__open_and_load();
if (!ASSERT_OK_PTR(skel, "cgroup_preorder__open_and_load"))
return -1;
err = setsockopt(sock_fd, SOL_IP, IP_TOS, &buf, 1);
if (!ASSERT_OK(err, "setsockopt"))
goto close_skel;
atype = bpf_program__expected_attach_type(skel->progs.child);
create_opts.flags = 0;
normal_link = bpf_link_create(bpf_program__fd(skel->progs.child),
cgroup_fd, atype, &create_opts);
if (!ASSERT_GE(normal_link, 0, "create_normal_link")) {
err = normal_link;
goto close_skel;
}
create_opts.flags = BPF_F_PREORDER;
preorder_link = bpf_link_create(bpf_program__fd(skel->progs.child_2),
cgroup_fd, atype, &create_opts);
if (!ASSERT_GE(preorder_link, 0, "create_preorder_link")) {
err = preorder_link;
goto close_links;
}
result = skel->bss->result;
skel->bss->idx = 0;
memset(result, 0, 4);
err = getsockopt(sock_fd, SOL_IP, IP_TOS, &buf, &optlen);
if (!ASSERT_OK(err, "getsockopt-before"))
goto close_links;
ASSERT_TRUE(result[0] == 2 && result[1] == 1, "order before update");
/* Replace the normal link's program child(1) -> parent(3). */
err = bpf_link_update(normal_link, bpf_program__fd(skel->progs.parent), NULL);
if (!ASSERT_OK(err, "bpf_link_update"))
goto close_links;
skel->bss->idx = 0;
memset(result, 0, 4);
err = getsockopt(sock_fd, SOL_IP, IP_TOS, &buf, &optlen);
if (!ASSERT_OK(err, "getsockopt-after"))
goto close_links;
ASSERT_TRUE(result[0] == 2 && result[1] == 3, "order after update");
close_links:
if (preorder_link >= 0)
close(preorder_link);
close(normal_link);
close_skel:
cgroup_preorder__destroy(skel);
return err;
}
void test_cgroup_preorder(void)
{
int cg_parent = -1, cg_child = -1, sock_fd = -1;
@ -120,6 +196,7 @@ void test_cgroup_preorder(void)
ASSERT_OK(run_getsockopt_test(cg_parent, cg_child, sock_fd, false), "getsockopt_test_1");
ASSERT_OK(run_getsockopt_test(cg_parent, cg_child, sock_fd, true), "getsockopt_test_2");
ASSERT_OK(run_link_replace_test(cg_child, sock_fd), "link_replace_test");
out:
close(sock_fd);