landlock: Change landlock_restrict_self(2) check ordering

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>

diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index a7396220c9d42c4b3df341235ab829c52790256b..507d43827afede055fc966318e991692f5e92d4b 100644 (file)
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -405,10 +405,6 @@ SYSCALL_DEFINE2(landlock_restrict_self, const int, ruleset_fd, const __u32,
        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, const int, ruleset_fd, const __u32,
            !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))

diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 18b779471dcbe7928f3d5dd90b8142295c67a08e..21fb335814194e729aee928842ddc18bf58790b0 100644 (file)
--- 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)