mount-util: Add a helper for remounting a bind mount

src/shared/mount-util.c

@@ -453,6 +453,16 @@ int bind_remount_one_with_mountinfo(
         return 0;
 }
 
+int bind_remount_one(const char *path, unsigned long new_flags, unsigned long flags_mask) {
+        _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
+
+        proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
+        if (!proc_self_mountinfo)
+                return log_debug_errno(errno, "Failed to open /proc/self/mountinfo: %m");
+
+        return bind_remount_one_with_mountinfo(path, new_flags, flags_mask, proc_self_mountinfo);
+}
+
 static int mount_switch_root_pivot(int fd_newroot, const char *path) {
         assert(fd_newroot >= 0);
         assert(path);

src/shared/mount-util.h

@@ -26,6 +26,7 @@ static inline int bind_remount_recursive(const char *prefix, unsigned long new_f
 }
 
 int bind_remount_one_with_mountinfo(const char *path, unsigned long new_flags, unsigned long flags_mask, FILE *proc_self_mountinfo);
+int bind_remount_one(const char *path, unsigned long new_flags, unsigned long flags_mask);
 
 int mount_switch_root_full(const char *path, unsigned long mount_propagation_flag, bool force_ms_move);
 static inline int mount_switch_root(const char *path, unsigned long mount_propagation_flag) {

src/test/test-mount-util.c

@@ -213,6 +213,25 @@ TEST(bind_remount_one) {
                 _exit(EXIT_SUCCESS);
         }
 
+        assert_se(wait_for_terminate_and_check("test-remount-one-with-mountinfo", pid, WAIT_LOG) == EXIT_SUCCESS);
+
+        pid = fork();
+        assert_se(pid >= 0);
+
+        if (pid == 0) {
+                /* child */
+
+                assert_se(detach_mount_namespace() >= 0);
+
+                assert_se(bind_remount_one("/run", MS_RDONLY, MS_RDONLY) >= 0);
+                assert_se(bind_remount_one("/run", MS_NOEXEC, MS_RDONLY|MS_NOEXEC) >= 0);
+                assert_se(bind_remount_one("/proc/idontexist", MS_RDONLY, MS_RDONLY) == -ENOENT);
+                assert_se(bind_remount_one("/proc/self", MS_RDONLY, MS_RDONLY) == -EINVAL);
+                assert_se(bind_remount_one("/", MS_RDONLY, MS_RDONLY) >= 0);
+
+                _exit(EXIT_SUCCESS);
+        }
+
         assert_se(wait_for_terminate_and_check("test-remount-one", pid, WAIT_LOG) == EXIT_SUCCESS);
 }