Magisk/native/jni/core/daemon.cpp

/* daemon.c - Magisk Daemon
 *
 * Start the daemon and wait for requests
 * Connect the daemon and send requests through sockets
 */

#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>
#include <sys/un.h>
#include <sys/types.h>
#include <sys/mount.h>

#include <magisk.h>
#include <utils.h>
#include <daemon.h>
#include <selinux.h>
#include <db.h>
#include <resetprop.h>
#include <flags.h>

int SDK_INT = -1;
struct stat SERVER_STAT;

static void verify_client(int client, pid_t pid) {
	// Verify caller is the same as server
	char path[32];
	sprintf(path, "/proc/%d/exe", pid);
	struct stat st{};
	stat(path, &st);
	if (st.st_dev != SERVER_STAT.st_dev || st.st_ino != SERVER_STAT.st_ino) {
		close(client);
		pthread_exit(nullptr);
	}
}

static void *request_handler(void *args) {
	int client = *((int *) args);
	delete (int *) args;

	struct ucred credential;
	get_client_cred(client, &credential);
	if (credential.uid != 0)
		verify_client(client, credential.pid);

	int req = read_int(client);
	switch (req) {
	case MAGISKHIDE:
	case POST_FS_DATA:
	case LATE_START:
	case BOOT_COMPLETE:
	case SQLITE_CMD:
		if (credential.uid != 0) {
			write_int(client, ROOT_REQUIRED);
			close(client);
			return nullptr;
		}
	default:
		break;
	}

	switch (req) {
	case MAGISKHIDE:
		magiskhide_handler(client);
		break;
	case SUPERUSER:
		su_daemon_handler(client, &credential);
		break;
	case CHECK_VERSION:
		write_string(client, MAGISK_VERSION ":MAGISK");
		close(client);
		break;
	case CHECK_VERSION_CODE:
		write_int(client, MAGISK_VER_CODE);
		close(client);
		break;
	case POST_FS_DATA:
		post_fs_data(client);
		break;
	case LATE_START:
		late_start(client);
		break;
	case BOOT_COMPLETE:
		boot_complete(client);
		break;
	case SQLITE_CMD:
		exec_sql(client);
		close(client);
		break;
	default:
		close(client);
		break;
	}
	return nullptr;
}

static void main_daemon() {
	android_logging();
	setsid();
	setcon("u:r:" SEPOL_PROC_DOMAIN ":s0");
	int fd = xopen("/dev/null", O_RDWR | O_CLOEXEC);
	xdup2(fd, STDOUT_FILENO);
	xdup2(fd, STDERR_FILENO);
	close(fd);
	fd = xopen("/dev/zero", O_RDWR | O_CLOEXEC);
	xdup2(fd, STDIN_FILENO);
	close(fd);

	LOGI(SHOW_VER(Magisk) " daemon started\n");

	// Get server stat
	stat("/proc/self/exe", &SERVER_STAT);

	// Get API level
	parse_prop_file("/system/build.prop", [](auto key, auto val) -> bool {
		if (strcmp(key, "ro.build.version.sdk") == 0) {
			LOGI("* Device API level: %s\n", val);
			SDK_INT = atoi(val);
			return false;
		}
		return true;
	});

	struct sockaddr_un sun;
	socklen_t len = setup_sockaddr(&sun, MAIN_SOCKET);
	fd = xsocket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
	if (xbind(fd, (struct sockaddr*) &sun, len))
		exit(1);
	xlisten(fd, 10);

	// Change process name
	strcpy(argv0, "magiskd");

	// Block all signals
	sigset_t block_set;
	sigfillset(&block_set);
	pthread_sigmask(SIG_SETMASK, &block_set, nullptr);

	// Loop forever to listen for requests
	for (;;) {
		int *client = new int;
		*client = xaccept4(fd, nullptr, nullptr, SOCK_CLOEXEC);
		new_daemon_thread(request_handler, client);
	}
}

int switch_mnt_ns(int pid) {
	char mnt[32];
	snprintf(mnt, sizeof(mnt), "/proc/%d/ns/mnt", pid);
	if (access(mnt, R_OK) == -1) return 1; // Maybe process died..

	int fd, ret;
	fd = xopen(mnt, O_RDONLY);
	if (fd < 0) return 1;
	// Switch to its namespace
	ret = xsetns(fd, 0);
	close(fd);
	return ret;
}

int connect_daemon() {
	struct sockaddr_un sun;
	socklen_t len = setup_sockaddr(&sun, MAIN_SOCKET);
	int fd = xsocket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
	if (connect(fd, (struct sockaddr*) &sun, len)) {
		if (getuid() != UID_ROOT || getgid() != UID_ROOT) {
			fprintf(stderr, "No daemon is currently running!\n");
			exit(1);
		}

		LOGD("client: launching new main daemon process\n");
		if (fork_dont_care() == 0) {
			close(fd);
			main_daemon();
		}

		while (connect(fd, (struct sockaddr*) &sun, len))
			usleep(10000);
	}
	return fd;
}