[PATCH 5.17 683/772] landlock: Change landlock_restrict_self(2) check ordering

Greg Kroah-Hartman
2022-06-07T21:54:34Z

From: Mickaël Salaün <mic@digikod.net>

commit eba39ca4b155c54adf471a69e91799cc1727873f upstream.

According to the Landlock goal to be a security feature available to
unprivileges processes, it makes more sense to first check for
no_new_privs before checking anything else (i.e. syscall arguments).

Merge inval_fd_enforce and unpriv_enforce_without_no_new_privs tests
into the new restrict_self_checks_ordering. This is similar to the
previous commit checking other syscalls.

Link: https://lore.kernel.org/r/20220506160820.524344-10-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
security/landlock/syscalls.c | 8 ++--
tools/testing/selftests/landlock/base_test.c | 47 +++++++++++++++++++++------
2 files changed, 41 insertions(+), 14 deletions(-)

--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -405,10 +405,6 @@ SYSCALL_DEFINE2(landlock_restrict_self,
if (!landlock_initialized)
return -EOPNOTSUPP;

- /* No flag for now. */
- if (flags)
- return -EINVAL;
-
/*
* Similar checks as for seccomp(2), except that an -EPERM may be
* returned.
@@ -417,6 +413,10 @@ SYSCALL_DEFINE2(landlock_restrict_self,
!ns_capable_noaudit(current_user_ns(), CAP_SYS_ADMIN))
return -EPERM;

+ /* No flag for now. */
+ if (flags)
+ return -EINVAL;
+
/* Gets and checks the ruleset. */
ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_READ);
if (IS_ERR(ruleset))
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -168,22 +168,49 @@ TEST(add_rule_checks_ordering)
ASSERT_EQ(0, close(ruleset_fd));
}

-TEST(inval_fd_enforce)
+/* Tests ordering of syscall argument and permission checks. */
+TEST(restrict_self_checks_ordering)
{
+ const struct landlock_ruleset_attr ruleset_attr = {
+ .handled_access_fs = LANDLOCK_ACCESS_FS_EXECUTE,
+ };
+ struct landlock_path_beneath_attr path_beneath_attr = {
+ .allowed_access = LANDLOCK_ACCESS_FS_EXECUTE,
+ .parent_fd = -1,
+ };
+ const int ruleset_fd =
+ landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+
+ ASSERT_LE(0, ruleset_fd);
+ path_beneath_attr.parent_fd =
+ open("/tmp", O_PATH | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
+ ASSERT_LE(0, path_beneath_attr.parent_fd);
+ ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+ &path_beneath_attr, 0));
+ ASSERT_EQ(0, close(path_beneath_attr.parent_fd));
+
+ /* Checks unprivileged enforcement without no_new_privs. */
+ drop_caps(_metadata);
+ ASSERT_EQ(-1, landlock_restrict_self(-1, -1));
+ ASSERT_EQ(EPERM, errno);
+ ASSERT_EQ(-1, landlock_restrict_self(-1, 0));
+ ASSERT_EQ(EPERM, errno);
+ ASSERT_EQ(-1, landlock_restrict_self(ruleset_fd, 0));
+ ASSERT_EQ(EPERM, errno);
+
ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));

+ /* Checks invalid flags. */
+ ASSERT_EQ(-1, landlock_restrict_self(-1, -1));
+ ASSERT_EQ(EINVAL, errno);
+
+ /* Checks invalid ruleset FD. */
ASSERT_EQ(-1, landlock_restrict_self(-1, 0));
ASSERT_EQ(EBADF, errno);
-}
-
-TEST(unpriv_enforce_without_no_new_privs)
-{
- int err;

- drop_caps(_metadata);
- err = landlock_restrict_self(-1, 0);
- ASSERT_EQ(EPERM, errno);
- ASSERT_EQ(err, -1);
+ /* Checks valid call. */
+ ASSERT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+ ASSERT_EQ(0, close(ruleset_fd));
}

TEST(ruleset_fd_io)