Hijack another binary for 2nd stage

Instead of using ptrace hacks, use another hack instead :D

native/jni/init/init.hpp

@@ -101,7 +101,7 @@ public:
 
 class SARFirstStageInit : public SARBase {
 private:
-	void traced_exec_init();
+	void prepare();
 protected:
 	void early_mount() override;
 public:
@@ -110,7 +110,8 @@ public:
 	};
 	void start() override {
 		early_mount();
-		traced_exec_init();
+		prepare();
+		exec_init();
 	}
 };
 

native/jni/init/mount.cpp

@@ -195,7 +195,8 @@ void SARBase::backup_files() {
 		backup_folder("/overlay.d", overlays);
 
 	full_read("/proc/self/exe", self.buf, self.sz);
-	full_read("/.backup/.magisk", config.buf, config.sz);
+	if (access("/.backup/.magisk", R_OK) == 0)
+		full_read("/.backup/.magisk", config.buf, config.sz);
 }
 
 void SARBase::mount_system_root() {
@@ -242,11 +243,9 @@ void SARFirstStageInit::early_mount() {
 
 void SecondStageInit::early_mount() {
 	backup_files();
-	rm_rf("/system");
-	rm_rf("/.backup");
-	rm_rf("/overlay.d");
 
-	umount2("/system/bin/init", MNT_DETACH);
+	umount2("/init", MNT_DETACH);
+	umount2("/proc/self/exe", MNT_DETACH);
 
 	if (access("/system_root", F_OK) == 0)
 		switch_root("/system_root");

native/jni/init/rootdir.cpp

@@ -131,9 +131,11 @@ bool MagiskInit::patch_sepolicy(const char *file) {
 		return false;
 	}
 
-	// Mount selinuxfs to communicate with kernel
-	xmount("selinuxfs", SELINUX_MNT, "selinuxfs", 0, nullptr);
-	mount_list.emplace_back(SELINUX_MNT);
+	if (access(SELINUX_VERSION, F_OK) != 0) {
+		// 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();
@@ -307,10 +309,10 @@ void SARBase::patch_rootdir() {
 	struct sockaddr_un sun;
 	int sockfd = xsocket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
 	if (connect(sockfd, (struct sockaddr*) &sun, setup_sockaddr(&sun, INIT_SOCKET)) == 0) {
-		LOGD("ACK init tracer to write backup files\n");
-		// Let tracer know where tmp_dir is
+		LOGD("ACK init daemon to write backup files\n");
+		// Let daemon know where tmp_dir is
 		write_string(sockfd, tmp_dir);
-		// Wait for tracer to finish copying files
+		// Wait for daemon to finish restoring files
 		int ack;
 		read(sockfd, &ack, sizeof(ack));
 	} else {

native/jni/init/twostage.cpp

@@ -1,6 +1,3 @@
-#include <sys/ptrace.h>
-#include <sys/wait.h>
-
 #include <magisk.hpp>
 #include <utils.hpp>
 #include <logging.hpp>
@@ -76,20 +73,41 @@ void FirstStageInit::prepare() {
 	chdir("/");
 }
 
-static inline long xptrace(int request, pid_t pid, void *addr, void *data) {
-	long ret = ptrace(request, pid, addr, data);
-	if (ret < 0)
-		PLOGE("ptrace %d", pid);
-	return ret;
-}
+#define INIT_PATH  "/system/bin/init"
+#define REDIR_PATH "/system/bin/adbd"
 
-static inline long xptrace(int request, pid_t pid, void *addr = nullptr, intptr_t data = 0) {
-	return xptrace(request, pid, addr, reinterpret_cast<void *>(data));
-}
-
-void SARFirstStageInit::traced_exec_init() {
+void SARFirstStageInit::prepare() {
 	int pid = getpid();
 
+	xmount("tmpfs", "/dev", "tmpfs", 0, "mode=755");
+
+	// Patch init binary
+	raw_data init;
+	int src = xopen("/init", O_RDONLY);
+	fd_full_read(src, init.buf, init.sz);
+	for (uint8_t *p = init.buf, *eof = init.buf + init.sz; p < eof; ++p) {
+		if (memcmp(p, INIT_PATH, sizeof(INIT_PATH)) == 0) {
+			LOGD("Patch init [" INIT_PATH "] -> [" REDIR_PATH "]\n");
+			memcpy(p, REDIR_PATH, sizeof(REDIR_PATH));
+			break;
+		}
+	}
+	int dest = xopen("/dev/init", O_CREAT | O_WRONLY, 0);
+	write(dest, init.buf, init.sz);
+	fclone_attr(src, dest);
+	close(dest);
+
+	// Replace redirect init with magiskinit
+	dest = xopen("/dev/magiskinit", O_CREAT | O_WRONLY, 0);
+	write(dest, self.buf, self.sz);
+	fclone_attr(src, dest);
+	close(src);
+	close(dest);
+
+	xmount("/dev/init", "/init", nullptr, MS_BIND, nullptr);
+	xmount("/dev/magiskinit", REDIR_PATH, nullptr, MS_BIND, nullptr);
+	xumount2("/dev", MNT_DETACH);
+
 	// Block SIGUSR1
 	sigset_t block, old;
 	sigemptyset(&block);
@@ -97,42 +115,22 @@ void SARFirstStageInit::traced_exec_init() {
 	sigprocmask(SIG_BLOCK, &block, &old);
 
 	if (int child = xfork(); child) {
-		LOGD("init tracer [%d]\n", child);
-		// Wait for children to attach
+		LOGD("init daemon [%d]\n", child);
+		// Wait for children signal
 		int sig;
 		sigwait(&block, &sig);
 
 		// Restore sigmask
-		sigprocmask(SIG_BLOCK, &old, nullptr);
-
-		// Re-exec init
-		exec_init();
+		sigprocmask(SIG_SETMASK, &old, nullptr);
 	} else {
-		// Attach to parent to trace exec
-		xptrace(PTRACE_ATTACH, pid);
-		waitpid(pid, nullptr, __WALL | __WNOTHREAD);
-		xptrace(PTRACE_SETOPTIONS, pid, nullptr, PTRACE_O_TRACEEXEC);
-		xptrace(PTRACE_CONT, pid, 0, SIGUSR1);
-
-		// Wait for execve
-		waitpid(pid, nullptr, __WALL | __WNOTHREAD);
-
-		// Swap out init with bind mount
-		xmount("tmpfs", "/dev", "tmpfs", 0, "mode=755");
-		int init = xopen("/dev/magiskinit", O_CREAT | O_WRONLY, 0750);
-		write(init, self.buf, self.sz);
-		close(init);
-		xmount("/dev/magiskinit", "/init", nullptr, MS_BIND, nullptr);
-		xumount2("/dev", MNT_DETACH);
-
 		// Establish socket for 2nd stage ack
 		struct sockaddr_un sun;
 		int sockfd = xsocket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
 		xbind(sockfd, (struct sockaddr*) &sun, setup_sockaddr(&sun, INIT_SOCKET));
 		xlisten(sockfd, 1);
 
-		// Resume init
-		xptrace(PTRACE_DETACH, pid);
+		// Resume parent
+		kill(pid, SIGUSR1);
 
 		// Wait for second stage ack
 		int client = xaccept4(sockfd, nullptr, nullptr, SOCK_CLOEXEC);