Properly detect 2SI init

Fix #2994

native/jni/init/getinfo.cpp

@@ -178,3 +178,10 @@ void load_kernel_info(cmdline *cmd) {
 	LOGD("hardware=[%s]\n", cmd->hardware);
 	LOGD("hardware.platform=[%s]\n", cmd->hardware_plat);
 }
+
+bool check_two_stage() {
+	if (access("/apex", F_OK) == 0)
+		return true;
+	auto init = raw_data::mmap_ro("/init");
+	return init.find("selinux_setup");
+}

native/jni/init/init.cpp

@@ -40,6 +40,14 @@ int data_holder::patch(str_pairs list) {
 	return count;
 }
 
+bool data_holder::find(string_view pattern) {
+	for (uint8_t *p = buf, *eof = buf + sz; p < eof; ++p) {
+		if (memcmp(p, pattern.data(), pattern.length() + 1) == 0)
+			return true;
+	}
+	return false;
+}
+
 void data_holder::consume(data_holder &other) {
 	buf = other.buf;
 	sz = other.sz;
@@ -47,16 +55,6 @@ void data_holder::consume(data_holder &other) {
 	other.sz = 0;
 }
 
-template <>
-auto_data<MMAP>::~auto_data<MMAP>() {
-	if (buf) munmap(buf, sz);
-}
-
-template <>
-auto_data<HEAP>::~auto_data<HEAP>() {
-	free(buf);
-}
-
 auto_data<HEAP> raw_data::read(int fd) {
 	auto_data<HEAP> data;
 	fd_full_read(fd, data.buf, data.sz);
@@ -75,9 +73,11 @@ auto_data<MMAP> raw_data::mmap_rw(const char *name) {
 	return data;
 }
 
-// Explicit instantiation
-template struct auto_data<HEAP>;
-template struct auto_data<MMAP>;
+auto_data<MMAP> raw_data::mmap_ro(const char *name) {
+	auto_data<MMAP> data;
+	::mmap_ro(name, data.buf, data.sz);
+	return data;
+}
 
 static bool unxz(int fd, const uint8_t *buf, size_t size) {
 	uint8_t out[8192];
@@ -229,7 +229,7 @@ int main(int argc, char *argv[]) {
 		// This will also mount /sys and /proc
 		load_kernel_info(&cmd);
 
-		bool two_stage = access("/apex", F_OK) == 0;
+		bool two_stage = check_two_stage();
 		if (cmd.skip_initramfs) {
 			if (two_stage)
 				init = new SARFirstStageInit(argv, &cmd);

native/jni/init/init.hpp

@@ -21,12 +21,12 @@ struct data_holder {
 	size_t sz = 0;
 	using str_pairs = std::initializer_list<std::pair<std::string_view, std::string_view>>;
 	int patch(str_pairs list);
+	bool find(std::string_view pattern);
 protected:
 	void consume(data_holder &other);
 };
 
 enum data_type { HEAP, MMAP };
-
 template <data_type T>
 struct auto_data : public data_holder {
 	auto_data<T>() = default;
@@ -35,11 +35,14 @@ struct auto_data : public data_holder {
 	~auto_data<T>() {}
 	auto_data<T>& operator=(auto_data<T> &&other) { consume(other); return *this; }
 };
+template <> inline auto_data<MMAP>::~auto_data<MMAP>() { if (buf) munmap(buf, sz); }
+template <> inline auto_data<HEAP>::~auto_data<HEAP>() { free(buf); }
 
 namespace raw_data {
 	auto_data<HEAP> read(const char *name);
 	auto_data<HEAP> read(int fd);
 	auto_data<MMAP> mmap_rw(const char *name);
+	auto_data<MMAP> mmap_ro(const char *name);
 }
 
 struct fstab_entry {
@@ -59,6 +62,7 @@ struct fstab_entry {
 #define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"
 
 void load_kernel_info(cmdline *cmd);
+bool check_two_stage();
 int dump_magisk(const char *path, mode_t mode);
 int magisk_proxy_main(int argc, char *argv[]);
 void setup_klog();