test: ensure 'InaccessiblePaths=/proc' option works (#6017)

Test case for PR #5985.

Makefile.am

@@ -1737,6 +1737,7 @@ TEST_DATA_FILES += \
 	test/test-execute/exec-readonlypaths-mount-propagation.service \
 	test/test-execute/exec-readwritepaths-mount-propagation.service \
 	test/test-execute/exec-inaccessiblepaths-mount-propagation.service \
+	test/test-execute/exec-inaccessiblepaths-proc.service \
 	test/test-execute/exec-spec-interpolation.service \
 	test/test-execute/exec-systemcallerrornumber.service \
 	test/test-execute/exec-systemcallfilter-failing2.service \

src/test/test-execute.c

@@ -233,6 +233,10 @@ static void test_exec_inaccessiblepaths(Manager *m) {
         test(m, "exec-inaccessiblepaths-mount-propagation.service", 0, CLD_EXITED);
 }
 
+static void test_exec_inaccessiblepaths_proc(Manager *m) {
+        test(m, "exec-inaccessiblepaths-proc.service", 0, CLD_EXITED);
+}
+
 static void test_exec_systemcallfilter(Manager *m) {
 #ifdef HAVE_SECCOMP
         if (!is_seccomp_available())
@@ -479,6 +483,7 @@ int main(int argc, char *argv[]) {
                 test_exec_readonlypaths,
                 test_exec_readwritepaths,
                 test_exec_inaccessiblepaths,
+                test_exec_inaccessiblepaths_proc,
                 test_exec_privatenetwork,
                 test_exec_systemcallfilter,
                 test_exec_systemcallerrornumber,

test/meson.build

@@ -85,6 +85,7 @@ test_data_files = '''
         test-execute/exec-readonlypaths-mount-propagation.service
         test-execute/exec-readwritepaths-mount-propagation.service
         test-execute/exec-inaccessiblepaths-mount-propagation.service
+        test-execute/exec-inaccessiblepaths-proc.service
         test-execute/exec-spec-interpolation.service
         test-execute/exec-systemcallerrornumber.service
         test-execute/exec-systemcallfilter-failing2.service

test/test-execute/exec-inaccessiblepaths-proc.service

@@ -0,0 +1,7 @@
+[Unit]
+Description=Test to make sure that mount namespace setup works properly with the 'InaccessiblePaths=/proc' option
+
+[Service]
+InaccessiblePaths=/proc
+ExecStart=/bin/sh -x -c 'test "$$(stat -c %%a /proc)" = "0"'
+Type=oneshot