Magisk/native/jni/magiskhide/proc_monitor.c

/* proc_monitor.c - Monitor am_proc_start events and unmount
 *
 * We monitor the logcat am_proc_start events. When a target starts up,
 * we pause it ASAP, and fork a new process to join its mount namespace
 * and do all the unmounting/mocking
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/mount.h>

#include "magisk.h"
#include "daemon.h"
#include "utils.h"
#include "magiskhide.h"

static int sockfd = -1;

// Workaround for the lack of pthread_cancel
static void term_thread(int sig) {
	LOGD("proc_monitor: running cleanup\n");
	destroy_list();
	hideEnabled = 0;
	close(sockfd);
	sockfd = -1;
	pthread_mutex_destroy(&hide_lock);
	pthread_mutex_destroy(&file_lock);
	LOGD("proc_monitor: terminating...\n");
	pthread_exit(NULL);
}

static int read_namespace(const int pid, char* target, const size_t size) {
	char path[32];
	sprintf(path, "/proc/%d/ns/mnt", pid);
	if (access(path, R_OK) == -1)
		return 1;
	xreadlink(path, target, size);
	return 0;
}

static void lazy_unmount(const char* mountpoint) {
	if (umount2(mountpoint, MNT_DETACH) != -1)
		LOGD("hide_daemon: Unmounted (%s)\n", mountpoint);
}

static int parse_ppid(int pid) {
	char stat[512], path[32];
	int fd, ppid;
	sprintf(path, "/proc/%d/stat", pid);
	fd = xopen(path, O_RDONLY);
	xread(fd, stat, sizeof(stat));
	close(fd);
	/* PID COMM STATE PPID ..... */
	sscanf(stat, "%*d %*s %*c %d", &ppid);
	return ppid;
}

static void hide_daemon(int pid) {
	LOGD("hide_daemon: start unmount for pid=[%d]\n", pid);

	char *line, buffer[PATH_MAX];
	struct vector mount_list;

	manage_selinux();
	clean_magisk_props();

	if (switch_mnt_ns(pid))
		goto exit;

	snprintf(buffer, sizeof(buffer), "/proc/%d/mounts", pid);
	vec_init(&mount_list);
	file_to_vector(buffer, &mount_list);

	// Unmount dummy skeletons and /sbin links
	vec_for_each(&mount_list, line) {
		if (strstr(line, "tmpfs /system/") || strstr(line, "tmpfs /vendor/") || strstr(line, "tmpfs /sbin")) {
			sscanf(line, "%*s %4096s", buffer);
			lazy_unmount(buffer);
		}
		free(line);
	}
	vec_destroy(&mount_list);

	// Re-read mount infos
	snprintf(buffer, sizeof(buffer), "/proc/%d/mounts", pid);
	vec_init(&mount_list);
	file_to_vector(buffer, &mount_list);

	// Unmount everything under /system, /vendor, and loop mounts
	vec_for_each(&mount_list, line) {
		if (strstr(line, "/dev/block/loop") || strstr(line, " /system/") || strstr(line, " /vendor/")) {
			sscanf(line, "%*s %4096s", buffer);
			lazy_unmount(buffer);
		}
		free(line);
	}
	vec_destroy(&mount_list);

exit:
	// Send resume signal
	kill(pid, SIGCONT);
	_exit(0);
}

void proc_monitor() {
	// Unblock user signals
	sigset_t block_set;
	sigemptyset(&block_set);
	sigaddset(&block_set, TERM_THREAD);
	pthread_sigmask(SIG_UNBLOCK, &block_set, NULL);

	// Register the cancel signal
	struct sigaction act;
	memset(&act, 0, sizeof(act));
	act.sa_handler = term_thread;
	sigaction(TERM_THREAD, &act, NULL);

	if (access("/proc/1/ns/mnt", F_OK) != 0) {
		LOGE("proc_monitor: Your kernel doesn't support mount namespace :(\n");
		term_thread(TERM_THREAD);
	}

	while(1) {
		// Connect to the log daemon
		connect_daemon2(LOG_DAEMON, &sockfd);
		write_int(sockfd, HIDE_CONNECT);

		FILE *log_in = fdopen(sockfd, "r");
		char buf[4096];
		while (fgets(buf, sizeof(buf), log_in)) {
			char *ss = strchr(buf, '[');
			int pid, ppid, num = 0;
			char *pos = ss, proc[256], ns[32], pns[32];

			while(1) {
				pos = strchr(pos, ',');
				if(pos == NULL)
					break;
				pos[0] = ' ';
				++num;
			}

			if(sscanf(ss, num == 6 ? "[%*d %d %*d %*d %256s" : "[%*d %d %*d %256s", &pid, proc) != 2)
				continue;

			// Make sure our target is alive
			if (kill(pid, 0))
				continue;

			// Allow hiding sub-services of applications
			char *colon = strchr(proc, ':');
			if (colon)
				*colon = '\0';

			int hide = 0;
			pthread_mutex_lock(&hide_lock);
			char *line;
			vec_for_each(hide_list, line) {
				if (strcmp(proc, line) == 0) {
					hide = 1;
					break;
				}
			}
			pthread_mutex_unlock(&hide_lock);
			if (!hide)
				continue;

			ppid = parse_ppid(pid);
			read_namespace(ppid, pns, sizeof(pns));
			do {
				read_namespace(pid, ns, sizeof(ns));
				if (strcmp(ns, pns) == 0)
					usleep(50);
				else
					break;
			} while (1);

			// Send pause signal ASAP
			if (kill(pid, SIGSTOP) == -1)
				continue;

			// Restore the colon so we can log the actual process name
			if (colon)
				*colon = ':';
#ifdef MAGISK_DEBUG
			LOGI("proc_monitor: %s (PID=[%d] ns=%s)(PPID=[%d] ns=%s)\n",
				 proc, pid, ns + 4, ppid, pns + 4);
#else
			LOGI("proc_monitor: %s\n", proc);
#endif

			/*
			 * The setns system call do not support multithread processes
			 * We have to fork a new process, setns, then do the unmounts
			 */
			if (fork_dont_care() == 0)
				hide_daemon(pid);
		}
		// The other end EOF, restart the connection
	}
}