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    Subject[PATCH AUTOSEL 5.15 170/188] bpf/selftests: Fix namespace mount setup in tc_redirect
    Date
    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;
    --
    2.34.1
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