Record mounts to be cleaned up in a vector

native/jni/init/early_mount.cpp

@@ -84,6 +84,14 @@ static bool is_lnk(const char *name) {
 	return S_ISLNK(st.st_mode);
 }
 
+void BaseInit::cleanup() {
+	// Unmount in reverse order
+	for (auto &p : reversed(mount_list)) {
+		LOGD("Unmount [%s]\n", p.data());
+		umount(p.data());
+	}
+}
+
 bool MagiskInit::read_dt_fstab(const char *name, char *partname, char *fstype) {
 	char path[128];
 	int fd;
@@ -118,7 +126,7 @@ if (!is_lnk("/" #name) && read_dt_fstab(#name, partname, fstype)) { \
 	setup_block(partname, block_dev); \
 	xmkdir("/" #name, 0755); \
 	xmount(block_dev, "/" #name, fstype, MS_RDONLY, nullptr); \
-	mnt_##name = true; \
+	mount_list.emplace_back("/" #name); \
 }
 
 void RootFSInit::early_mount() {
@@ -237,16 +245,3 @@ void SecondStageInit::early_mount() {
 
 	switch_root("/system_root");
 }
-
-#define umount_root(name) \
-if (mnt_##name) \
-	umount("/" #name);
-
-void MagiskInit::cleanup() {
-	umount(SELINUX_MNT);
-	BaseInit::cleanup();
-	umount_root(system);
-	umount_root(vendor);
-	umount_root(product);
-	umount_root(odm);
-}

native/jni/init/init.h

@@ -1,6 +1,7 @@
 #include <sys/mount.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <vector>
 
 struct cmdline {
 	bool system_as_root;
@@ -34,19 +35,17 @@ class BaseInit {
 protected:
 	cmdline *cmd;
 	char **argv;
+	std::vector<std::string> mount_list;
 
 	void exec_init(const char *init = "/init") {
 		cleanup();
 		execv(init, argv);
 		exit(1);
 	}
-	virtual void cleanup() {
-		umount("/sys");
-		umount("/proc");
-		umount("/dev");
-	}
+	virtual void cleanup();
 public:
-	BaseInit(char *argv[], cmdline *cmd) : cmd(cmd), argv(argv) {}
+	BaseInit(char *argv[], cmdline *cmd) :
+	cmd(cmd), argv(argv), mount_list{"/sys", "/proc", "/dev"} {}
 	virtual ~BaseInit() = default;
 	virtual void start() = 0;
 };
@@ -54,15 +53,10 @@ public:
 class MagiskInit : public BaseInit {
 protected:
 	raw_data self;
-	bool mnt_system = false;
-	bool mnt_vendor = false;
-	bool mnt_product = false;
-	bool mnt_odm = false;
 
 	virtual void early_mount() = 0;
 	bool read_dt_fstab(const char *name, char *partname, char *fstype);
 	bool patch_sepolicy(const char *file = "/sepolicy");
-	void cleanup() override;
 public:
 	MagiskInit(char *argv[], cmdline *cmd) : BaseInit(argv, cmd) {};
 };

native/jni/init/rootdir.cpp

@@ -167,6 +167,7 @@ bool MagiskInit::patch_sepolicy(const char *file) {
 
 	// Mount selinuxfs to communicate with kernel
 	xmount("selinuxfs", SELINUX_MNT, "selinuxfs", 0, nullptr);
+	mount_list.emplace_back(SELINUX_MNT);
 
 	if (patch_init)
 		load_split_cil();
@@ -230,7 +231,7 @@ static void sbin_overlay(const raw_data &self, const raw_data &config) {
 #define PATCHPOLICY "/sbin/.se"
 #define LIBSELINUX  "/system/" LIBNAME "/libselinux.so"
 
-static string mount_list;
+static string magic_mount_list;
 
 static void magic_mount(int dirfd, const string &path) {
 	DIR *dir = xfdopendir(dirfd);
@@ -248,8 +249,8 @@ static void magic_mount(int dirfd, const string &path) {
 				string src = ROOTOVL + dest;
 				LOGD("Mount [%s] -> [%s]\n", src.data(), dest.data());
 				xmount(src.data(), dest.data(), nullptr, MS_BIND, nullptr);
-				mount_list += dest;
-				mount_list += '\n';
+				magic_mount_list += dest;
+				magic_mount_list += '\n';
 			}
 		}
 	}
@@ -379,7 +380,7 @@ void SARBase::patch_rootdir() {
 	magic_mount(src, "");
 	close(src);
 	dest = xopen(ROOTMNT, O_WRONLY | O_CREAT | O_CLOEXEC);
-	write(dest, mount_list.data(), mount_list.length());
+	write(dest, magic_mount_list.data(), magic_mount_list.length());
 	close(dest);
 }
 

native/jni/utils/misc.h

@@ -59,6 +59,25 @@ private:
 	std::function<void()> fn;
 };
 
+template <typename T>
+class reversed_container {
+public:
+	reversed_container(T &base) : base(base) {}
+	decltype(std::declval<T>().rbegin()) begin() { return base.rbegin(); }
+	decltype(std::declval<T>().crbegin()) begin() const { return base.crbegin(); }
+	decltype(std::declval<T>().crbegin()) cbegin() const { return base.crbegin(); }
+	decltype(std::declval<T>().rend()) end() { return base.rend(); }
+	decltype(std::declval<T>().crend()) end() const { return base.crend(); }
+	decltype(std::declval<T>().crend()) cend() const { return base.crend(); }
+private:
+	T &base;
+};
+
+template <typename T>
+reversed_container<T> reversed(T &base) {
+	return reversed_container<T>(base);
+}
+
 static inline int parse_int(std::string s) { return parse_int(s.data()); }
 
 static inline int parse_int(std::string_view s) { return parse_int(s.data()); }