Harden socket verification

- Do not allow connections to magiskd from binaries other than the one started the server
- Do not allow connections to magisklogd without root access

native/jni/core/daemon.cpp

@@ -23,21 +23,30 @@
 #include "flags.h"
 
 int SDK_INT = -1;
+struct stat SERVER_STAT;
 
-static void get_client_cred(int fd, struct ucred *cred) {
-	socklen_t ucred_length = sizeof(*cred);
-	if(getsockopt(fd, SOL_SOCKET, SO_PEERCRED, cred, &ucred_length))
-		PLOGE("getsockopt");
+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;
-	int req = read_int(client);
 
 	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:
@@ -103,6 +112,11 @@ static void main_daemon() {
 	xdup2(fd, STDIN_FILENO);
 	close(fd);
 
+	LOGI("Magisk v" xstr(MAGISK_VERSION) "(" xstr(MAGISK_VER_CODE) ") 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) {
@@ -119,7 +133,6 @@ static void main_daemon() {
 	if (xbind(fd, (struct sockaddr*) &sun, len))
 		exit(1);
 	xlisten(fd, 10);
-	LOGI("Magisk v" xstr(MAGISK_VERSION) "(" xstr(MAGISK_VER_CODE) ") daemon started\n");
 
 	// Change process name
 	strcpy(argv0, "magiskd");
@@ -138,7 +151,7 @@ static void main_daemon() {
 	sigaction(SIGPIPE, &act, nullptr);
 
 	// Loop forever to listen for requests
-	while(1) {
+	while(true) {
 		int *client = new int;
 		*client = xaccept4(fd, nullptr, nullptr, SOCK_CLOEXEC);
 		pthread_t thread;

native/jni/core/log_daemon.cpp

@@ -166,6 +166,13 @@ static void log_daemon() {
 	xlisten(sockfd, 10);
 	while(true) {
 		int fd = xaccept4(sockfd, nullptr, nullptr, SOCK_CLOEXEC);
+		struct ucred credential;
+		get_client_cred(fd, &credential);
+		if (credential.uid != 0) {
+			// Do not allow non root clients
+			close(fd);
+			continue;
+		}
 		switch(read_int(fd)) {
 			case HIDE_CONNECT:
 				pthread_mutex_lock(&lock);

native/jni/core/socket.cpp

@@ -11,7 +11,7 @@
 #include "utils.h"
 #include "magisk.h"
 
-#define ABS_SOCKET_LEN(sun) (sizeof(sun->sun_family) + strlen(sun->sun_path + 1) + 1)
+#define ABS_SOCKET_LEN(sun) (sizeof(sa_family_t) + strlen(sun->sun_path + 1) + 1)
 
 socklen_t setup_sockaddr(struct sockaddr_un *sun, const char *name) {
 	memset(sun, 0, sizeof(*sun));
@@ -38,6 +38,11 @@ int socket_accept(int sockfd, int timeout) {
 	return xpoll(&pfd, 1, timeout * 1000) <= 0 ? -1 : xaccept4(sockfd, NULL, NULL, SOCK_CLOEXEC);
 }
 
+void get_client_cred(int fd, struct ucred *cred) {
+	socklen_t ucred_length = sizeof(*cred);
+	getsockopt(fd, SOL_SOCKET, SO_PEERCRED, cred, &ucred_length);
+}
+
 /*
  * Receive a file descriptor from a Unix socket.
  * Contributed by @mkasick

native/jni/include/daemon.h

@@ -48,6 +48,7 @@ bool start_log_daemon();
 socklen_t setup_sockaddr(struct sockaddr_un *sun, const char *name);
 int create_rand_socket(struct sockaddr_un *sun);
 int socket_accept(int sockfd, int timeout);
+void get_client_cred(int fd, struct ucred *cred);
 int recv_fd(int sockfd);
 void send_fd(int sockfd, int fd);
 int read_int(int fd);