From: Jiri Olsa jolsa@redhat.com

[ Upstream commit 5e22dd18626726028a93ff1350a8a71a00fd843d ]

The tc_redirect umounts /sys in the new namespace, which can be mounted as shared and cause global umount. The lazy umount also takes down mounted trees under /sys like debugfs, which won't be available after sysfs mounts again and could cause fails in other tests.

# cat /proc/self/mountinfo | grep debugfs 34 23 0:7 / /sys/kernel/debug rw,nosuid,nodev,noexec,relatime shared:14 - debugfs debugfs rw # cat /proc/self/mountinfo | grep sysfs 23 86 0:22 / /sys rw,nosuid,nodev,noexec,relatime shared:2 - sysfs sysfs rw # mount | grep debugfs debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)

# ./test_progs -t tc_redirect #164 tc_redirect:OK Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED

# mount | grep debugfs # cat /proc/self/mountinfo | grep debugfs # cat /proc/self/mountinfo | grep sysfs 25 86 0:22 / /sys rw,relatime shared:2 - sysfs sysfs rw

Making the sysfs private under the new namespace so the umount won't trigger the global sysfs umount.

Reported-by: Hangbin Liu haliu@redhat.com Signed-off-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Cc: Jussi Maki joamaki@gmail.com Link: https://lore.kernel.org/bpf/20220104121030.138216-1-jolsa@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/bpf/prog_tests/tc_redirect.c | 7 +++++++ 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/tc_redirect.c b/tools/testing/selftests/bpf/prog_tests/tc_redirect.c index e7201ba29ccd6..47e3159729d21 100644 --- a/tools/testing/selftests/bpf/prog_tests/tc_redirect.c +++ b/tools/testing/selftests/bpf/prog_tests/tc_redirect.c @@ -105,6 +105,13 @@ static int setns_by_fd(int nsfd) if (!ASSERT_OK(err, "unshare")) return err;

+ /* Make our /sys mount private, so the following umount won't + * trigger the global umount in case it's shared. + */ + err = mount("none", "/sys", NULL, MS_PRIVATE, NULL); + if (!ASSERT_OK(err, "remount private /sys")) + return err; + err = umount2("/sys", MNT_DETACH); if (!ASSERT_OK(err, "umount2 /sys")) return err;