Magisk/native/jni/core/init.cpp

#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/sendfile.h>
#include <sys/sysmacros.h>
#include <linux/input.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <fcntl.h>
#include <libgen.h>
#include <functional>
#include <string_view>

#include <xz.h>
#include <magisk.h>
#include <magiskpolicy.h>
#include <selinux.h>
#include <cpio.h>
#include <utils.h>
#include <flags.h>

#include "binaries.h"
#ifdef USE_64BIT
#include "binaries_arch64.h"
#define LIBNAME "lib64"
#else
#include "binaries_arch.h"
#define LIBNAME "lib"
#endif
#include "magiskrc.h"

using namespace std;

#define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"

#ifdef MAGISK_DEBUG
static FILE *kmsg;
static char kbuf[4096];
static int vprintk(const char *fmt, va_list ap) {
	vsprintf(kbuf, fmt, ap);
	return fprintf(kmsg, "magiskinit: %s", kbuf);
}

static void setup_klog() {
	mknod("/kmsg", S_IFCHR | 0666, makedev(1, 11));
	int fd = xopen("/kmsg", O_WRONLY | O_CLOEXEC);
	kmsg = fdopen(fd, "w");
	setbuf(kmsg, nullptr);
	unlink("/kmsg");
	log_cb.d = log_cb.i = log_cb.w = log_cb.e = vprintk;
	log_cb.ex = nop_ex;
}
#else
#define setup_klog(...)
#endif

static int test_main(int argc, char *argv[]);

constexpr const char *init_applet[] =
		{ "magiskpolicy", "supolicy", "init_test", nullptr };
constexpr int (*init_applet_main[])(int, char *[]) =
		{ magiskpolicy_main, magiskpolicy_main, test_main, nullptr };

struct cmdline {
	bool system_as_root;
	char slot[3];
	char dt_dir[128];
};

struct raw_data {
	void *buf;
	size_t sz;
};

static bool unxz(int fd, const uint8_t *buf, size_t size) {
	uint8_t out[8192];
	xz_crc32_init();
	struct xz_dec *dec = xz_dec_init(XZ_DYNALLOC, 1 << 26);
	struct xz_buf b = {
			.in = buf,
			.in_pos = 0,
			.in_size = size,
			.out = out,
			.out_pos = 0,
			.out_size = sizeof(out)
	};
	enum xz_ret ret;
	do {
		ret = xz_dec_run(dec, &b);
		if (ret != XZ_OK && ret != XZ_STREAM_END)
			return false;
		write(fd, out, b.out_pos);
		b.out_pos = 0;
	} while (b.in_pos != size);
	return true;
}

static void decompress_ramdisk() {
	constexpr char tmp[] = "tmp.cpio";
	constexpr char ramdisk_xz[] = "ramdisk.cpio.xz";
	if (access(ramdisk_xz, F_OK))
		return;
	LOGD("Decompressing ramdisk from %s\n", ramdisk_xz);
	uint8_t *buf;
	size_t sz;
	mmap_ro(ramdisk_xz, buf, sz);
	int fd = open(tmp, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC);
	unxz(fd, buf, sz);
	munmap(buf, sz);
	close(fd);
	cpio_mmap cpio(tmp);
	cpio.extract();
	unlink(tmp);
	unlink(ramdisk_xz);
}

static int dump_magisk(const char *path, mode_t mode) {
	int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, mode);
	if (fd < 0)
		return 1;
	if (!unxz(fd, magisk_xz, sizeof(magisk_xz)))
		return 1;
	close(fd);
	return 0;
}

static int dump_manager(const char *path, mode_t mode) {
	int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, mode);
	if (fd < 0)
		return 1;
	if (!unxz(fd, manager_xz, sizeof(manager_xz)))
		return 1;
	close(fd);
	return 0;
}

class MagiskInit {
private:
	cmdline cmd{};
	raw_data self{};
	raw_data config{};
	int root = -1;
	char **argv;
	bool load_sepol = false;
	bool mnt_system = false;
	bool mnt_vendor = false;
	bool mnt_product = false;
	bool mnt_odm = false;

	void load_kernel_info();
	void preset();
	void early_mount();
	void setup_rootfs();
	bool read_dt_fstab(const char *name, char *partname, char *partfs);
	bool patch_sepolicy();
	void cleanup();
	void re_exec_init();

public:
	explicit MagiskInit(char *argv[]) : argv(argv) {}
	void start();
	void test();
};

static inline void parse_cmdline(const std::function<void (std::string_view, const char *)> &fn) {
	char cmdline[4096];
	int fd = open("/proc/cmdline", O_RDONLY | O_CLOEXEC);
	cmdline[read(fd, cmdline, sizeof(cmdline))] = '\0';
	close(fd);

	char *tok, *eql, *tmp, *saveptr;
	saveptr = cmdline;
	while ((tok = strtok_r(nullptr, " \n", &saveptr)) != nullptr) {
		eql = strchr(tok, '=');
		if (eql) {
			*eql = '\0';
			if (eql[1] == '"') {
				tmp = strchr(saveptr, '"');
				if (tmp != nullptr) {
					*tmp = '\0';
					saveptr[-1] = ' ';
					saveptr = tmp + 1;
					eql++;
				}
			}
			fn(tok, eql + 1);
		} else {
			fn(tok, "");
		}
	}
}

#define test_bit(bit, array) (array[bit / 8] & (1 << (bit % 8)))

static bool check_key_combo() {
	uint8_t bitmask[(KEY_MAX + 1) / 8];
	vector<int> events;
	constexpr const char *name = "/event";

	for (int minor = 64; minor < 96; ++minor) {
		if (mknod(name, S_IFCHR | 0444, makedev(13, minor))) {
			PLOGE("mknod");
			continue;
		}
		int fd = open(name, O_RDONLY | O_CLOEXEC);
		unlink(name);
		if (fd < 0)
			continue;
		memset(bitmask, 0, sizeof(bitmask));
		ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(bitmask)), bitmask);
		if (test_bit(KEY_VOLUMEUP, bitmask))
			events.push_back(fd);
	}

	if (events.empty())
		return false;

	RunFinally fin([&]() -> void {
		for (const int &fd : events)
			close(fd);
	});

	// Return true if volume key up is hold for more than 3 seconds
	int count = 0;
	for (int i = 0; i < 500; ++i) {
		for (const int &fd : events) {
			memset(bitmask, 0, sizeof(bitmask));
			ioctl(fd, EVIOCGKEY(sizeof(bitmask)), bitmask);
			if (test_bit(KEY_VOLUMEUP, bitmask)) {
				count++;
				break;
			}
		}
		if (count >= 300) {
			LOGD("KEY_VOLUMEUP detected: disable system-as-root\n");
			return true;
		}
		// Check every 10ms
		usleep(10000);
	}
	return false;
}

void MagiskInit::load_kernel_info() {
	// Communicate with kernel using procfs and sysfs
	xmkdir("/proc", 0755);
	xmount("proc", "/proc", "proc", 0, nullptr);
	xmkdir("/sys", 0755);
	xmount("sysfs", "/sys", "sysfs", 0, nullptr);

	bool enter_recovery = false;
	bool kirin = false;
	bool recovery_mode = false;

	parse_cmdline([&](auto key, auto value) -> void {
		LOGD("cmdline: [%s]=[%s]\n", key.data(), value);
		if (key == "androidboot.slot_suffix") {
			strcpy(cmd.slot, value);
		} else if (key == "androidboot.slot") {
			cmd.slot[0] = '_';
			strcpy(cmd.slot + 1, value);
		} else if (key == "skip_initramfs") {
			cmd.system_as_root = true;
		} else if (key == "androidboot.android_dt_dir") {
			strcpy(cmd.dt_dir, value);
		} else if (key == "enter_recovery") {
			enter_recovery = value[0] == '1';
		} else if (key == "androidboot.hardware") {
			kirin = strstr(value, "kirin") || strstr(value, "hi3660");
		}
	});

	parse_prop_file("/.backup/.magisk", [&](auto key, auto value) -> bool {
		if (key == "RECOVERYMODE" && value == "true")
			recovery_mode = true;
		return true;
	});

	if (kirin && enter_recovery) {
		// Inform that we are actually booting as recovery
		if (!recovery_mode) {
			if (FILE *f = fopen("/.backup/.magisk", "ae"); f) {
				fprintf(f, "RECOVERYMODE=true\n");
				fclose(f);
			}
			recovery_mode = true;
		}
	}

	if (recovery_mode) {
		LOGD("Running in recovery mode, waiting for key...\n");
		cmd.system_as_root = !check_key_combo();
	}

	if (cmd.dt_dir[0] == '\0')
		strcpy(cmd.dt_dir, DEFAULT_DT_DIR);

	LOGD("system_as_root=[%d]\n", cmd.system_as_root);
	LOGD("slot=[%s]\n", cmd.slot);
	LOGD("dt_dir=[%s]\n", cmd.dt_dir);
}

void MagiskInit::preset() {
	root = open("/", O_RDONLY | O_CLOEXEC);

	if (cmd.system_as_root) {
		// Clear rootfs
		LOGD("Cleaning rootfs\n");
		frm_rf(root, { "overlay", "proc", "sys" });
	} else {
		decompress_ramdisk();

		// Revert original init binary
		rename("/.backup/init", "/init");
		rm_rf("/.backup");

		// Do not go further if device is booting into recovery
		if (access("/sbin/recovery", F_OK) == 0) {
			LOGD("Ramdisk is recovery, abort\n");
			re_exec_init();
		}
	}
}

struct device {
	int major;
	int minor;
	char devname[32];
	char partname[32];
};

static inline void parse_device(device *dev, const char *uevent) {
	dev->partname[0] = '\0';
	FILE *fp = xfopen(uevent, "re");
	char buf[64];
	while (fgets(buf, sizeof(buf), fp)) {
		if (strncmp(buf, "MAJOR", 5) == 0) {
			sscanf(buf, "MAJOR=%d", &dev->major);
		} else if (strncmp(buf, "MINOR", 5) == 0) {
			sscanf(buf, "MINOR=%d", &dev->minor);
		} else if (strncmp(buf, "DEVNAME", 7) == 0) {
			sscanf(buf, "DEVNAME=%s", dev->devname);
		} else if (strncmp(buf, "PARTNAME", 8) == 0) {
			sscanf(buf, "PARTNAME=%s", dev->partname);
		}
	}
	fclose(fp);
}

static vector<device> dev_list;

static void collect_devices() {
	char path[128];
	struct dirent *entry;
	device dev;
	DIR *dir = xopendir("/sys/dev/block");
	if (dir == nullptr)
		return;
	while ((entry = readdir(dir))) {
		if (entry->d_name == "."sv || entry->d_name == ".."sv)
			continue;
		sprintf(path, "/sys/dev/block/%s/uevent", entry->d_name);
		parse_device(&dev, path);
		dev_list.push_back(dev);
	}
	closedir(dir);
}

static bool setup_block(const char *partname, char *block_dev) {
	if (dev_list.empty())
		collect_devices();
	for (auto &dev : dev_list) {
		if (strcasecmp(dev.partname, partname) == 0) {
			sprintf(block_dev, "/dev/block/%s", dev.devname);
			LOGD("Found %s: [%s] (%d, %d)\n", dev.partname, dev.devname, dev.major, dev.minor);
			xmkdir("/dev", 0755);
			xmkdir("/dev/block", 0755);
			mknod(block_dev, S_IFBLK | 0600, makedev(dev.major, dev.minor));
			return true;
		}
	}
	return false;
}

bool MagiskInit::read_dt_fstab(const char *name, char *partname, char *partfs) {
	char path[128];
	int fd;
	sprintf(path, "%s/fstab/%s/dev", cmd.dt_dir, name);
	if ((fd = xopen(path, O_RDONLY | O_CLOEXEC)) >= 0) {
		read(fd, path, sizeof(path));
		close(fd);
		// Some custom treble use different names, so use what we read
		char *part = rtrim(strrchr(path, '/') + 1);
		sprintf(partname, "%s%s", part, strend(part, cmd.slot) ? cmd.slot : "");
		sprintf(path, "%s/fstab/%s/type", cmd.dt_dir, name);
		if ((fd = xopen(path, O_RDONLY | O_CLOEXEC)) >= 0) {
			read(fd, partfs, 32);
			close(fd);
			return true;
		}
	}
	return false;
}

static inline bool is_lnk(const char *name) {
	struct stat st;
	if (lstat(name, &st))
		return false;
	return S_ISLNK(st.st_mode);
}

#define link_root(name) \
if (is_lnk("/system_root" name)) \
	cp_afc("/system_root" name, name)

#define mount_root(name) \
if (!is_lnk("/" #name) && read_dt_fstab(#name, partname, fstype)) { \
	LOGD("Early mount " #name "\n"); \
	setup_block(partname, block_dev); \
	xmkdir("/" #name, 0755); \
	xmount(block_dev, "/" #name, fstype, MS_RDONLY, nullptr); \
	mnt_##name = true; \
}

void MagiskInit::early_mount() {
	char partname[32];
	char fstype[32];
	char block_dev[64];

	if (cmd.system_as_root) {
		LOGD("Early mount system_root\n");
		sprintf(partname, "system%s", cmd.slot);
		setup_block(partname, block_dev);
		xmkdir("/system_root", 0755);
		xmount(block_dev, "/system_root", "ext4", MS_RDONLY, nullptr);
		xmkdir("/system", 0755);
		xmount("/system_root/system", "/system", nullptr, MS_BIND, nullptr);

		// Android Q
		if (is_lnk("/system_root/init"))
			load_sepol = true;

		// System-as-root with monolithic sepolicy
		if (access("/system_root/sepolicy", F_OK) == 0)
			cp_afc("/system_root/sepolicy", "/sepolicy");

		// Copy if these partitions are symlinks
		link_root("/vendor");
		link_root("/product");
		link_root("/odm");
	} else {
		mount_root(system);
	}

	mount_root(vendor);
	mount_root(product);
	mount_root(odm);
}

static void patch_socket_name(const char *path) {
	uint8_t *buf;
	char name[sizeof(MAIN_SOCKET)];
	size_t size;
	mmap_rw(path, buf, size);
	for (int i = 0; i < size; ++i) {
		if (memcmp(buf + i, MAIN_SOCKET, sizeof(MAIN_SOCKET)) == 0) {
			gen_rand_str(name, sizeof(name));
			memcpy(buf + i, name, sizeof(name));
			i += sizeof(name);
		}
	}
	munmap(buf, size);
}

constexpr const char wrapper[] =
"#!/system/bin/sh\n"
"export LD_LIBRARY_PATH=\"$LD_LIBRARY_PATH:/apex/com.android.runtime/" LIBNAME "\"\n"
"exec /sbin/magisk.bin \"$0\" \"$@\"\n"
;

void MagiskInit::setup_rootfs() {
	bool patch_init = patch_sepolicy();

	if (cmd.system_as_root) {
		// Clone rootfs
		LOGD("Clone root dir from system to rootfs\n");
		int system_root = xopen("/system_root", O_RDONLY | O_CLOEXEC);
		clone_dir(system_root, root, false);
		close(system_root);
	}

	if (patch_init) {
		constexpr char SYSTEM_INIT[] = "/system/bin/init";
		// If init is symlink, copy it to rootfs so we can patch
		if (is_lnk("/init"))
			cp_afc(SYSTEM_INIT, "/init");

		char *addr;
		size_t size;
		mmap_rw("/init", addr, size);
		for (char *p = addr; p < addr + size; ++p) {
			if (memcmp(p, SPLIT_PLAT_CIL, sizeof(SPLIT_PLAT_CIL)) == 0) {
				// Force init to load /sepolicy
				LOGD("Remove from init: " SPLIT_PLAT_CIL "\n");
				memset(p, 'x', sizeof(SPLIT_PLAT_CIL) - 1);
				p += sizeof(SPLIT_PLAT_CIL) - 1;
			} else if (memcmp(p, SYSTEM_INIT, sizeof(SYSTEM_INIT)) == 0) {
				// Force execute /init instead of /system/bin/init
				LOGD("Patch init: [/system/bin/init] -> [/init]\n");
				strcpy(p, "/init");
				p += sizeof(SYSTEM_INIT) - 1;
			}
		}
		munmap(addr, size);
	}

	// Handle ramdisk overlays
	int fd = open("/overlay", O_RDONLY | O_CLOEXEC);
	if (fd >= 0) {
		LOGD("Merge overlay folder\n");
		mv_dir(fd, root);
		close(fd);
		rmdir("/overlay");
	}

	// Patch init.rc
	FILE *rc = xfopen("/init.p.rc", "we");
	file_readline("/init.rc", [&](auto line) -> bool {
		// Do not start vaultkeeper
		if (str_contains(line, "start vaultkeeper")) {
			LOGD("Remove vaultkeeper\n");
			return true;
		}
		// Do not run flash_recovery
		if (str_starts(line, "service flash_recovery")) {
			LOGD("Remove flash_recovery\n");
			fprintf(rc, "service flash_recovery /system/bin/xxxxx\n");
			return true;
		}
		// Else just write the line
		fprintf(rc, "%s", line.data());
		return true;
	});
	char pfd_svc[8], ls_svc[8], bc_svc[8];
	// Make sure to be unique
	pfd_svc[0] = 'a';
	ls_svc[0] = '0';
	bc_svc[0] = 'A';
	gen_rand_str(pfd_svc + 1, sizeof(pfd_svc) - 1);
	gen_rand_str(ls_svc + 1, sizeof(ls_svc) - 1);
	gen_rand_str(bc_svc + 1, sizeof(bc_svc) - 1);
	LOGD("Inject magisk services: [%s] [%s] [%s]\n", pfd_svc, ls_svc, bc_svc);
	fprintf(rc, magiskrc, pfd_svc, pfd_svc, ls_svc, bc_svc, bc_svc);
	fclose(rc);
	clone_attr("/init.rc", "/init.p.rc");
	rename("/init.p.rc", "/init.rc");

	// Don't let init run in init yet
	lsetfilecon("/init", "u:object_r:rootfs:s0");

	// Create hardlink mirror of /sbin to /root
	mkdir("/root", 0750);
	clone_attr("/sbin", "/root");
	int rootdir = xopen("/root", O_RDONLY | O_CLOEXEC);
	int sbin = xopen("/sbin", O_RDONLY | O_CLOEXEC);
	link_dir(sbin, rootdir);
	close(sbin);

	LOGD("Mount /sbin tmpfs overlay\n");
	xmount("tmpfs", "/sbin", "tmpfs", 0, "mode=755");
	sbin = xopen("/sbin", O_RDONLY | O_CLOEXEC);

	char path[64];

	// Create symlinks pointing back to /root
	DIR *dir = xfdopendir(rootdir);
	struct dirent *entry;
	while((entry = xreaddir(dir))) {
		if (entry->d_name == "."sv || entry->d_name == ".."sv)
			continue;
		sprintf(path, "/root/%s", entry->d_name);
		xsymlinkat(path, sbin, entry->d_name);
	}

	// Dump binaries
	mkdir(MAGISKTMP, 0755);
	fd = xopen(MAGISKTMP "/config", O_WRONLY | O_CREAT, 0000);
	write(fd, config.buf, config.sz);
	close(fd);
	fd = xopen("/sbin/magiskinit", O_WRONLY | O_CREAT, 0755);
	write(fd, self.buf, self.sz);
	close(fd);
	if (access("/system/apex", F_OK) == 0) {
		LOGD("APEX detected, use wrapper\n");
		dump_magisk("/sbin/magisk.bin", 0755);
		patch_socket_name("/sbin/magisk.bin");
		fd = xopen("/sbin/magisk", O_WRONLY | O_CREAT, 0755);
		write(fd, wrapper, sizeof(wrapper) - 1);
		close(fd);
	} else {
		dump_magisk("/sbin/magisk", 0755);
		patch_socket_name("/sbin/magisk");
	}

	// Create applet symlinks
	for (int i = 0; applet_names[i]; ++i) {
		sprintf(path, "/sbin/%s", applet_names[i]);
		xsymlink("/sbin/magisk", path);
	}
	for (int i = 0; init_applet[i]; ++i) {
		sprintf(path, "/sbin/%s", init_applet[i]);
		xsymlink("/sbin/magiskinit", path);
	}

	close(rootdir);
	close(sbin);
}

bool MagiskInit::patch_sepolicy() {
	bool patch_init = false;

	if (access(SPLIT_PLAT_CIL, R_OK) == 0) {
		LOGD("sepol: split policy\n");
		patch_init = true;
	} else if (access("/sepolicy", R_OK) == 0) {
		LOGD("sepol: monolithic policy\n");
		load_policydb("/sepolicy");
	} else {
		LOGD("sepol: no selinux\n");
		return false;
	}

	// Mount selinuxfs to communicate with kernel
	xmount("selinuxfs", SELINUX_MNT, "selinuxfs", 0, nullptr);

	if (patch_init)
		load_split_cil();

	sepol_magisk_rules();
	sepol_allow(SEPOL_PROC_DOMAIN, ALL, ALL, ALL);
	dump_policydb("/sepolicy");

	// Load policy to kernel so we can label rootfs
	if (load_sepol) {
		LOGD("sepol: preload sepolicy\n");
		dump_policydb(SELINUX_LOAD);
	}

	// Remove OnePlus stupid debug sepolicy and use our own
	if (access("/sepolicy_debug", F_OK) == 0) {
		unlink("/sepolicy_debug");
		link("/sepolicy", "/sepolicy_debug");
	}

	// Enable selinux functions
	selinux_builtin_impl();

	return patch_init;
}

#define umount_root(name) \
if (mnt_##name) \
	umount("/" #name);

void MagiskInit::cleanup() {
	umount(SELINUX_MNT);
	umount("/sys");
	umount("/proc");
	umount_root(system);
	umount_root(vendor);
	umount_root(product);
	umount_root(odm);
}

void MagiskInit::re_exec_init() {
	LOGD("Re-exec /init\n");
	cleanup();
	execv("/init", argv);
	exit(1);
}

void MagiskInit::start() {
	// Prevent file descriptor confusion
	mknod("/null", S_IFCHR | 0666, makedev(1, 3));
	int null = open("/null", O_RDWR | O_CLOEXEC);
	unlink("/null");
	xdup3(null, STDIN_FILENO, O_CLOEXEC);
	xdup3(null, STDOUT_FILENO, O_CLOEXEC);
	xdup3(null, STDERR_FILENO, O_CLOEXEC);
	if (null > STDERR_FILENO)
		close(null);

	setup_klog();

	load_kernel_info();

	full_read("/init", &self.buf, &self.sz);
	full_read("/.backup/.magisk", &config.buf, &config.sz);

	preset();
	early_mount();
	setup_rootfs();
	re_exec_init();
}

void MagiskInit::test() {
	cmdline_logging();
	log_cb.ex = nop_ex;

	chdir(dirname(argv[0]));
	chroot(".");
	chdir("/");

	load_kernel_info();
	preset();
	early_mount();
	setup_rootfs();
	cleanup();
}

static int test_main(int, char *argv[]) {
	MagiskInit init(argv);
	init.test();
	return 0;
}

int main(int argc, char *argv[]) {
	umask(0);

	for (int i = 0; init_applet[i]; ++i) {
		if (strcmp(basename(argv[0]), init_applet[i]) == 0)
			return (*init_applet_main[i])(argc, argv);
	}

	if (argc > 1 && strcmp(argv[1], "-x") == 0) {
		if (strcmp(argv[2], "magisk") == 0)
			return dump_magisk(argv[3], 0755);
		else if (strcmp(argv[2], "manager") == 0)
			return dump_manager(argv[3], 0644);
	}

	if (getpid() != 1)
		return 1;

	MagiskInit init(argv);

	// Run the main routine
	init.start();
}