Add magisk daemon

jni/daemon/daemon.c

@@ -0,0 +1,88 @@
+/* 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 <sys/un.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+
+#include "magisk.h"
+#include "utils.h"
+#include "daemon.h"
+
+static void request_handler(int client) {
+	/* TODO: Put all function entrypoints here
+	   it'll currently just log the input string */
+	char *s = read_string(client);
+	close(client);
+	LOGI("%s\n", s);
+	free(s);
+}
+
+/* Setup the address and return socket fd */
+static int setup_socket(struct sockaddr_un *sun) {
+	int fd = xsocket(AF_LOCAL, SOCK_STREAM, 0);
+	if (fcntl(fd, F_SETFD, FD_CLOEXEC)) {
+	    PLOGE("fcntl FD_CLOEXEC");
+	}
+
+	memset(sun, 0, sizeof(*sun));
+	sun->sun_family = AF_LOCAL;
+	memcpy(sun->sun_path, REQUESTOR_DAEMON_PATH, REQUESTOR_DAEMON_PATH_LEN);
+	return fd;
+}
+
+void start_daemon() {
+	// Launch the daemon, create new session, set proper context
+	if (getuid() != AID_ROOT || getgid() != AID_ROOT) {
+		PLOGE("daemon requires root. uid/gid not root");
+	}
+	switch (fork()) {
+	case -1:
+		PLOGE("fork");
+	case 0:
+		break;
+	default:
+		return;
+	}
+	xsetsid();
+	xsetcon("u:r:su:s0");
+
+	struct sockaddr_un sun;
+	int fd = setup_socket(&sun);
+	
+	xbind(fd, (struct sockaddr*) &sun, sizeof(sun));
+	xlisten(fd, 10);
+
+	// Change process name
+	strcpy(argv0, "magisk_daemon");
+
+	// Loop forever to listen to requests
+	while(1) {
+		request_handler(xaccept(fd, NULL, NULL));
+	}
+}
+
+/* Connect the daemon, and return a socketfd */
+int connect_daemon() {
+	struct sockaddr_un sun;
+	int fd = setup_socket(&sun);
+	if (connect(fd, (struct sockaddr*) &sun, sizeof(sun))) {
+		/* If we cannot access the daemon, we start the daemon
+		 * since there is no clear entry point when the daemon should be started
+		 */
+		start_daemon();
+		do {
+			// Wait for 10ms
+			usleep(10000);
+		} while (connect(fd, (struct sockaddr*) &sun, sizeof(sun)));
+	}
+	return fd;
+}

jni/daemon/daemon.h

@@ -0,0 +1,10 @@
+/* daemon.h - Utility functions for daemon-client communication
+ */
+
+// socket_trans.c
+int recv_fd(int sockfd);
+void send_fd(int sockfd, int fd);
+int read_int(int fd);
+void write_int(int fd, int val);
+char* read_string(int fd);
+void write_string(int fd, const char* val);

jni/daemon/socket_trans.c

@@ -0,0 +1,146 @@
+/* socket_trans.c - Functions to transfer data through socket
+ */
+
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include "magisk.h"
+#include "utils.h"
+#include "daemon.h"
+
+/*
+ * Receive a file descriptor from a Unix socket.
+ * Contributed by @mkasick
+ *
+ * Returns the file descriptor on success, or -1 if a file
+ * descriptor was not actually included in the message
+ *
+ * On error the function terminates by calling exit(-1)
+ */
+int recv_fd(int sockfd) {
+    // Need to receive data from the message, otherwise don't care about it.
+    char iovbuf;
+
+    struct iovec iov = {
+        .iov_base = &iovbuf,
+        .iov_len  = 1,
+    };
+
+    char cmsgbuf[CMSG_SPACE(sizeof(int))];
+
+    struct msghdr msg = {
+        .msg_iov        = &iov,
+        .msg_iovlen     = 1,
+        .msg_control    = cmsgbuf,
+        .msg_controllen = sizeof(cmsgbuf),
+    };
+
+    xrecvmsg(sockfd, &msg, MSG_WAITALL);
+
+    // Was a control message actually sent?
+    switch (msg.msg_controllen) {
+    case 0:
+        // No, so the file descriptor was closed and won't be used.
+        return -1;
+    case sizeof(cmsgbuf):
+        // Yes, grab the file descriptor from it.
+        break;
+    default:
+        goto error;
+    }
+
+    struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+
+    if (cmsg             == NULL                  ||
+        cmsg->cmsg_len   != CMSG_LEN(sizeof(int)) ||
+        cmsg->cmsg_level != SOL_SOCKET            ||
+        cmsg->cmsg_type  != SCM_RIGHTS) {
+error:
+        LOGE("unable to read fd");
+        exit(-1);
+    }
+
+    return *(int *)CMSG_DATA(cmsg);
+}
+
+/*
+ * Send a file descriptor through a Unix socket.
+ * Contributed by @mkasick
+ *
+ * On error the function terminates by calling exit(-1)
+ *
+ * fd may be -1, in which case the dummy data is sent,
+ * but no control message with the FD is sent.
+ */
+void send_fd(int sockfd, int fd) {
+    // Need to send some data in the message, this will do.
+    struct iovec iov = {
+        .iov_base = "",
+        .iov_len  = 1,
+    };
+
+    struct msghdr msg = {
+        .msg_iov        = &iov,
+        .msg_iovlen     = 1,
+    };
+
+    char cmsgbuf[CMSG_SPACE(sizeof(int))];
+
+    if (fd != -1) {
+        // Is the file descriptor actually open?
+        if (fcntl(fd, F_GETFD) == -1) {
+            if (errno != EBADF) {
+                PLOGE("unable to send fd");
+            }
+            // It's closed, don't send a control message or sendmsg will EBADF.
+        } else {
+            // It's open, send the file descriptor in a control message.
+            msg.msg_control    = cmsgbuf;
+            msg.msg_controllen = sizeof(cmsgbuf);
+
+            struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+
+            cmsg->cmsg_len   = CMSG_LEN(sizeof(int));
+            cmsg->cmsg_level = SOL_SOCKET;
+            cmsg->cmsg_type  = SCM_RIGHTS;
+
+            *(int *)CMSG_DATA(cmsg) = fd;
+        }
+    }
+
+    xsendmsg(sockfd, &msg, 0);
+}
+
+int read_int(int fd) {
+    int val;
+    xxread(fd, &val, sizeof(int));
+    return val;
+}
+
+void write_int(int fd, int val) {
+    xwrite(fd, &val, sizeof(int));
+}
+
+char* read_string(int fd) {
+    int len = read_int(fd);
+    if (len > PATH_MAX || len < 0) {
+        LOGE("invalid string length %d", len);
+        exit(1);
+    }
+    char* val = xmalloc(sizeof(char) * (len + 1));
+    xxread(fd, val, len);
+    val[len] = '\0';
+    return val;
+}
+
+void write_string(int fd, const char* val) {
+    int len = strlen(val);
+    write_int(fd, len);
+    xwrite(fd, val, len);
+}