On 11/6/22 11:42 PM, Hou Tao wrote:
From: Hou Tao <houtao1@xxxxxxxxxx>
The test closes both iterator link fd and cgroup fd, and removes the
cgroup file to make a dead cgroup before reading cgroup iterator fd. It
also uses kern_sync_rcu() and usleep() to wait for the release of
start cgroup. If the start cgroup is not pinned by cgroup iterator,
reading iterator fd will trigger use-after-free.
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
LGTM with a few nits below.
Acked-by: Yonghong Song <yhs@xxxxxx>
---
.../selftests/bpf/prog_tests/cgroup_iter.c | 78 +++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
index c4a2adb38da1..d64ed1cf1554 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter.c
@@ -189,6 +189,82 @@ static void test_walk_self_only(struct cgroup_iter *skel)
BPF_CGROUP_ITER_SELF_ONLY, "self_only");
}
+static void test_walk_dead_self_only(struct cgroup_iter *skel)
+{
+ DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+ char expected_output[128], buf[128];
+ const char *cgrp_name = "/dead";
+ union bpf_iter_link_info linfo;
+ int len, cgrp_fd, iter_fd;
+ struct bpf_link *link;
+ size_t left;
+ char *p;
+
+ cgrp_fd = create_and_get_cgroup(cgrp_name);
+ if (!ASSERT_GE(cgrp_fd, 0, "create cgrp"))
+ return;
+
+ /* The cgroup is already dead during iteration, so it only has epilogue
+ * in the output.
+ */
Let us reword the comment like
The cgroup will be dead during read() iteration, and it only has
epilogue in the output.
+ snprintf(expected_output, sizeof(expected_output), EPILOGUE);
+
+ memset(&linfo, 0, sizeof(linfo));
+ linfo.cgroup.cgroup_fd = cgrp_fd;
+ linfo.cgroup.order = BPF_CGROUP_ITER_SELF_ONLY;
+ opts.link_info = &linfo;
+ opts.link_info_len = sizeof(linfo);
+
+ link = bpf_program__attach_iter(skel->progs.cgroup_id_printer, &opts);
+ if (!ASSERT_OK_PTR(link, "attach_iter"))
+ goto close_cg;
+
+ iter_fd = bpf_iter_create(bpf_link__fd(link));
+ if (!ASSERT_GE(iter_fd, 0, "iter_create"))
+ goto free_link;
+
+ /* Close link fd and cgroup fd */
+ bpf_link__destroy(link);
+ link = NULL;
+ close(cgrp_fd);
+ cgrp_fd = -1;
We can remove 'link = NULL' and 'cgroup_fd = -1' and
add 'return' after 'close(iter_fd)', which seems better
to understand the code.
+
+ /* Remove cgroup to mark it as dead */
+ remove_cgroup(cgrp_name);
+
+ /* Two kern_sync_rcu() and usleep() pair are used to wait for the
+ * releases of cgroup css, and the last kern_sync_rcu() and usleep()
+ * pair is used to wait for the free of cgroup itself.
+ */
+ kern_sync_rcu();
+ usleep(8000);
+ kern_sync_rcu();
+ usleep(8000);
+ kern_sync_rcu();
+ usleep(1000);
+
+ memset(buf, 0, sizeof(buf));
+ left = ARRAY_SIZE(buf);
+ p = buf;
+ while ((len = read(iter_fd, p, left)) > 0) {
+ p += len;
+ left -= len;
+ }
+
+ ASSERT_STREQ(buf, expected_output, "dead cgroup output");
+
+ /* read() after iter finishes should be ok. */
+ if (len == 0)
+ ASSERT_OK(read(iter_fd, buf, sizeof(buf)), "second_read");
+
+ close(iter_fd);
+free_link:
+ bpf_link__destroy(link);
+close_cg:
+ if (cgrp_fd >= 0)
+ close(cgrp_fd);
+}
+
void test_cgroup_iter(void)
{
struct cgroup_iter *skel = NULL;
@@ -217,6 +293,8 @@ void test_cgroup_iter(void)
test_early_termination(skel);
if (test__start_subtest("cgroup_iter__self_only"))
test_walk_self_only(skel);
+ if (test__start_subtest("cgroup_iter_dead_self_only"))
Let us follow the convention in this file with
cgroup_iter__dead_self_only
+ test_walk_dead_self_only(skel);
out:
cgroup_iter__destroy(skel);
cleanup_cgroups();
