core: reorder systemd arguments on reexec

When reexecuting system let's put our arguments carrying deserialization
info first followed by any existing arguments to make sure they get
parsed in case we get weird stuff from the kernel cmdline (like --).

See: systemd/systemd#28184
(cherry picked from commit 06afda6)
(cherry picked from commit 884ab38)
(cherry picked from commit 163be31)

Author: mrc0mmand

src/core/main.c

@@ -1793,13 +1793,17 @@ static int do_reexecute(
                 xsprintf(sfd, "--deserialize=%i", fileno(arg_serialization));
 
                 i = 1;         /* Leave args[0] empty for now. */
-                filter_args(args, &i, argv, argc);
 
+                /* Put our stuff first to make sure it always gets parsed in case
+                 * we get weird stuff from the kernel cmdline (like --) */
                 if (switch_root_dir)
                         args[i++] = "--switched-root";
 
                 args[i++] = arg_system ? "--system" : "--user";
                 args[i++] = sfd;
+
+                filter_args(args, &i, argv, argc);
+
                 args[i++] = NULL;
 
                 assert(i <= args_size);

test/TEST-01-BASIC/test.sh

@@ -7,6 +7,11 @@ IMAGE_NAME="basic"
 RUN_IN_UNPRIVILEGED_CONTAINER=${RUN_IN_UNPRIVILEGED_CONTAINER:-yes}
 TEST_REQUIRE_INSTALL_TESTS=0
 
+# Check if we can correctly deserialize if the kernel cmdline contains "weird" stuff
+# like an invalid argument, "end of arguments" separator, or a sysvinit argument (-z)
+# See: https://github.com/systemd/systemd/issues/28184
+KERNEL_APPEND="foo -- -z bar --- baz $KERNEL_APPEND"
+
 # shellcheck source=test/test-functions
 . "${TEST_BASE_DIR:?}/test-functions"