Test the log buffers before running command

native/jni/core/log_monitor.c

@@ -16,6 +16,7 @@
 #include "daemon.h"
 
 int loggable = 1;
+static struct vector log_cmd, clear_cmd;
 static int sockfd;
 static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 
@@ -49,18 +50,6 @@ static struct log_listener events[] = {
 };
 #define EVENT_NUM (sizeof(events) / sizeof(struct log_listener))
 
-static void test_logcat() {
-	int log_fd = -1, log_pid;
-	char buf[1];
-	log_pid = exec_command(0, &log_fd, NULL, "logcat", NULL);
-	if (read(log_fd, buf, sizeof(buf)) != sizeof(buf)) {
-		loggable = 0;
-		LOGD("magisklogd: cannot read from logcat, disable logging");
-	}
-	kill(log_pid, SIGTERM);
-	waitpid(log_pid, NULL, 0);
-}
-
 static void sigpipe_handler(int sig) {
 	close(events[HIDE_EVENT].fd);
 	events[HIDE_EVENT].fd = -1;
@@ -93,12 +82,12 @@ static void *monitor_thread(void *args) {
 	// Give the main daemon some time before we monitor it
 	sleep(5);
 	int fd;
-	char b[1];
+	char b;
 	do {
 		fd = connect_daemon();
 		write_int(fd, MONITOR);
 		// This should hold unless the daemon is killed
-		read(fd, b, sizeof(b));
+		read(fd, &b, sizeof(b));
 		// The main daemon crashed, spawn a new one
 		close(fd);
 	} while (1);
@@ -131,17 +120,27 @@ void log_daemon() {
 	rename(LOGFILE, LOGFILE ".bak");
 	events[LOG_EVENT].fd = xopen(LOGFILE, O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC | O_APPEND, 0644);
 
+	// Construct cmdline
+	vec_init(&log_cmd);
+	vec_push_back(&log_cmd, "/system/bin/logcat");
+	// Test whether these buffers actually works
+	const char* b[] = { "main", "events", "crash" };
+	for (int i = 0; i < 3; ++i) {
+		if (exec_command_sync("/system/bin/logcat", "-b", b[i], "-d", "-f", "/dev/null", NULL) == 0)
+			vec_push_back_all(&log_cmd, "-b", b[i], NULL);
+	}
+	vec_dup(&log_cmd, &clear_cmd);
+	vec_push_back_all(&log_cmd, "-v", "threadtime", "-s", "am_proc_start", "Magisk", "*:F", NULL);
+	vec_push_back(&log_cmd, NULL);
+	vec_push_back(&clear_cmd, "-c");
+	vec_push_back(&clear_cmd, NULL);
+
 	int log_fd = -1, log_pid;
 	char line[PIPE_BUF];
 
 	while (1) {
 		// Start logcat
-		log_pid = exec_command(0, &log_fd, NULL,
+		log_pid = exec_array(0, &log_fd, NULL, (char **) vec_entry(&log_cmd));
-							   "/system/bin/logcat",
-							   "-b", "events", "-b", "main", "-b", "crash",
-							   "-v", "threadtime",
-							   "-s", "am_proc_start", "Magisk", "*:F",
-							   NULL);
 		FILE *logs = fdopen(log_fd, "r");
 		while (fgets(line, sizeof(line), logs)) {
 			if (line[0] == '-')
@@ -162,13 +161,14 @@ void log_daemon() {
 
 		LOGI("magisklogd: logcat output EOF");
 		// Clear buffer
-		exec_command_sync("logcat", "-b", "events", "-b", "main", "-b", "crash", "-c", NULL);
+		log_pid = exec_array(0, NULL, NULL, (char **) vec_entry(&clear_cmd));
+		waitpid(log_pid, NULL, 0);
 	}
 }
 
 /* Start new threads to monitor logcat and dump to logfile */
 void monitor_logs() {
-	test_logcat();
+	loggable = exec_command_sync("/system/bin/logcat", "-d", "-f", "/dev/null", NULL) == 0;
 	if (loggable) {
 		int fd;
 		connect_daemon2(LOG_DAEMON, &fd);

native/jni/include/utils.h

@@ -83,7 +83,8 @@ void ps(void (*func)(int));
 void ps_filter_proc_name(const char *filter, void (*func)(int));
 void unlock_blocks();
 void setup_sighandlers(void (*handler)(int));
-int exec_command(int err, int *fd, void (*setupenv)(struct vector*), const char *argv0, ...);
+int exec_array(int err, int *fd, void (*setenv)(struct vector *), char *const *argv);
+int exec_command(int err, int *fd, void (*setenv)(struct vector*), const char *argv0, ...);
 int exec_command_sync(char *const argv0, ...);
 int bind_mount(const char *from, const char *to);
 void get_client_cred(int fd, struct ucred *cred);

native/jni/include/vector.h

@@ -14,11 +14,12 @@ struct vector {
 
 void vec_init(struct vector *v);
 void vec_push_back(struct vector *v, void *p);
+void vec_push_back_all(struct vector *v, void *p, ...);
 void *vec_pop_back(struct vector *v);
 void vec_sort(struct vector *v, int (*compar)(const void *, const void *));
 void vec_destroy(struct vector *v);
 void vec_deep_destroy(struct vector *v);
-struct vector *vec_dup(struct vector *v);
+void vec_dup(struct vector *v, struct vector *vv);
 
 #define vec_size(v) (v)->size
 #define vec_cap(v) (v)->cap

native/jni/utils/misc.c

@@ -245,9 +245,9 @@ void setup_sighandlers(void (*handler)(int)) {
    fd == NULL -> Ignore output
   *fd < 0     -> Open pipe and set *fd to the read end
   *fd >= 0    -> STDOUT (or STDERR) will be redirected to *fd
-  *cb         -> A callback function which runs after fork
+  *setenv     -> A callback function which sets up a vector of environment variables
 */
-static int v_exec_command(int err, int *fd, void (*setupenv)(struct vector*), const char *argv0, va_list argv) {
+int exec_array(int err, int *fd, void (*setenv)(struct vector *), char *const *argv) {
 	int pipefd[2], writeEnd = -1;
 
 	if (fd) {
@@ -260,20 +260,12 @@ static int v_exec_command(int err, int *fd, void (*setupenv)(struct vector*), co
 		}
 	}
 
-	// Collect va_list into vector
-	struct vector args;
-	vec_init(&args);
-	vec_push_back(&args, strdup(argv0));
-	for (void *arg = va_arg(argv, void*); arg; arg = va_arg(argv, void*))
-		vec_push_back(&args, strdup(arg));
-	vec_push_back(&args, NULL);
-
 	// Setup environment
 	char *const *envp;
 	struct vector env;
 	vec_init(&env);
-	if (setupenv) {
+	if (setenv) {
-		setupenv(&env);
+		setenv(&env);
 		envp = (char **) vec_entry(&env);
 	} else {
 		extern char **environ;
@@ -287,21 +279,34 @@ static int v_exec_command(int err, int *fd, void (*setupenv)(struct vector*), co
 			*fd = pipefd[0];
 			close(pipefd[1]);
 		}
-		vec_deep_destroy(&args);
 		vec_deep_destroy(&env);
 		return pid;
 	}
 
 	if (fd) {
 		xdup2(writeEnd, STDOUT_FILENO);
-		if (err) xdup2(writeEnd, STDERR_FILENO);
+		if (err)
+			xdup2(writeEnd, STDERR_FILENO);
 	}
 
-	execvpe(argv0, (char **) vec_entry(&args), envp);
+	execvpe(argv[0], argv, envp);
-	PLOGE("execvpe %s", argv0);
+	PLOGE("execvpe %s", argv[0]);
 	return -1;
 }
 
+static int v_exec_command(int err, int *fd, void (*setenv)(struct vector*), const char *argv0, va_list argv) {
+	// Collect va_list into vector
+	struct vector args;
+	vec_init(&args);
+	vec_push_back(&args, strdup(argv0));
+	for (void *arg = va_arg(argv, void*); arg; arg = va_arg(argv, void*))
+		vec_push_back(&args, strdup(arg));
+	vec_push_back(&args, NULL);
+	int pid = exec_array(err, fd, setenv, (char **) vec_entry(&args));
+	vec_deep_destroy(&args);
+	return pid;
+}
+
 int exec_command_sync(char *const argv0, ...) {
 	va_list argv;
 	va_start(argv, argv0);
@@ -314,10 +319,10 @@ int exec_command_sync(char *const argv0, ...) {
 	return WEXITSTATUS(status);
 }
 
-int exec_command(int err, int *fd, void (*setupenv)(struct vector*), const char *argv0, ...) {
+int exec_command(int err, int *fd, void (*setenv)(struct vector*), const char *argv0, ...) {
 	va_list argv;
 	va_start(argv, argv0);
-	int pid = v_exec_command(err, fd, setupenv, argv0, argv);
+	int pid = v_exec_command(err, fd, setenv, argv0, argv);
 	va_end(argv);
 	return pid;
 }

native/jni/utils/vector.c

@@ -3,6 +3,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <stdarg.h>
 
 #include "vector.h"
 
@@ -23,6 +24,15 @@ void vec_push_back(struct vector *v, void *p) {
 	++vec_size(v);
 }
 
+void vec_push_back_all(struct vector *v, void *p, ...) {
+	va_list argv;
+	va_start(argv, p);
+	vec_push_back(v, p);
+	for (void *arg = va_arg(argv, char*); arg; arg = va_arg(argv, char*))
+		vec_push_back(v, arg);
+	va_end(argv);
+}
+
 void *vec_pop_back(struct vector *v) {
 	void *ret = vec_entry(v)[vec_size(v) - 1];
 	--vec_size(v);
@@ -73,11 +83,9 @@ void vec_deep_destroy(struct vector *v) {
 	vec_destroy(v);
 }
 
-struct vector *vec_dup(struct vector *v) {
+void vec_dup(struct vector *v, struct vector *vv) {
-	struct vector *ret = malloc(sizeof(*ret));
+	vec_size(vv) = vec_size(v);
-	vec_size(ret) = vec_size(v);
+	vec_cap(vv) = vec_cap(v);
-	vec_cap(ret) = vec_cap(v);
+	vec_entry(vv) = malloc(sizeof(void*) * vec_cap(v));
-	vec_entry(v) = malloc(sizeof(void*) * vec_cap(ret));
+	memcpy(vec_entry(vv), vec_entry(v), sizeof(void*) * vec_cap(v));
-	memcpy(vec_entry(ret), vec_entry(v), sizeof(void*) * vec_cap(ret));
-	return ret;
 }