Fix MagiskHide unmount daemon

Close #1101

native/jni/magiskhide/proc_monitor.cpp

@@ -95,41 +95,52 @@ static bool is_snet(const int pid) {
 }
 
 static void hide_daemon(int pid) {
-	char buffer[4096];
+	RunFinally fin([=]() -> void {
+		// Send resume signal
+		kill(pid, SIGCONT);
+		_exit(0);
+	});
+
 	if (switch_mnt_ns(pid))
-		goto exit;
+		return;
 
 	LOGD("hide_daemon: handling PID=[%d]\n", pid);
 	manage_selinux();
 	clean_magisk_props();
-	snprintf(buffer, sizeof(buffer), "/proc/%d", pid);
-	chdir(buffer);
+
+	vector<string> targets;
 
 	// Unmount dummy skeletons and /sbin links
-	file_readline("mounts", [&](string_view &s) -> bool {
+	file_readline("/proc/self/mounts", [&](string_view &s) -> bool {
 		if (str_contains(s, "tmpfs /system/") || str_contains(s, "tmpfs /vendor/") ||
 			str_contains(s, "tmpfs /sbin")) {
-			sscanf(s.data(), "%*s %4096s", buffer);
-			lazy_unmount(buffer);
+			char *path = (char *) s.data();
+			// Skip first token
+			strtok_r(nullptr, " ", &path);
+			targets.emplace_back(strtok_r(nullptr, " ", &path));
 		}
 		return true;
 	});
 
+	for (auto &s : targets)
+		lazy_unmount(s.data());
+	targets.clear();
+
 	// Unmount everything under /system, /vendor, and data mounts
-	file_readline("mounts", [&](string_view &s) -> bool {
+	file_readline("/proc/self/mounts", [&](string_view &s) -> bool {
 		if ((str_contains(s, " /system/") || str_contains(s, " /vendor/")) &&
 			(str_contains(s, system_block) || str_contains(s, vendor_block) ||
 			 str_contains(s, data_block))) {
-			sscanf(s.data(), "%*s %4096s", buffer);
-			lazy_unmount(buffer);
+			char *path = (char *) s.data();
+			// Skip first token
+			strtok_r(nullptr, " ", &path);
+			targets.emplace_back(strtok_r(nullptr, " ", &path));
 		}
 		return true;
 	});
 
-exit:
-	// Send resume signal
-	kill(pid, SIGCONT);
-	_exit(0);
+	for (auto &s : targets)
+		lazy_unmount(s.data());
 }
 
 // A mapping from pid to namespace inode to avoid time-consuming GC

native/jni/utils/include/utils.h

@@ -146,11 +146,7 @@ void write_zero(int fd, size_t size);
 #define str_contains(s, ss) ((ss) != nullptr && (s).find(ss) != std::string::npos)
 #define str_starts(s, ss) ((ss) != nullptr && (s).compare(0, strlen(ss), ss) == 0)
 
-// file.cpp
-
-void file_readline(const char *filename, const std::function<bool (std::string_view&)> &fn, bool trim = false);
-
-// misc.cpp
+// RAII
 
 class MutexGuard {
 public:
@@ -170,6 +166,22 @@ private:
 	pthread_mutex_t *mutex;
 };
 
+class RunFinally {
+public:
+	explicit RunFinally(std::function<void()> &&fn): fn(std::move(fn)) {}
+
+	~RunFinally() { fn(); }
+
+private:
+	const std::function<void ()> fn;
+};
+
+// file.cpp
+
+void file_readline(const char *filename, const std::function<bool (std::string_view&)> &fn, bool trim = false);
+
+// misc.cpp
+
 int new_daemon_thread(void *(*start_routine) (void *), void *arg = nullptr,
 		const pthread_attr_t *attr = nullptr);