much work (run as a daemon, drop priviliges, set priority, etc).

1 files changed, 126 insertions, 16 deletions

diff --git a/marsond.c b/marsond.c
index 885a3e2..f872baf 100644
--- a/marsond.c
+++ b/marsond.c
@@ -7,6 +7,12 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <stdarg.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <grp.h>
+
+#include <sys/resource.h>
+#include <sys/mman.h>
 
 #include <linux/input.h>
 #include <linux/uinput.h>
@@ -17,9 +23,13 @@
 
 #define DEFAULT_KBD "/dev/input/by-id/usb-Marson_Marson_Keyboard_and_Mouse_Link_Ver:ps2120L-event-kbd"
 
+#define DEFAULT_USER  "nobody"
+#define DEFAULT_GROUP "nobody"
+
 const char *self;
 
 int debugging = 0;                      /* -v */
+int foreground = 0;                     /* -v */
 const char *keyboard_dev = DEFAULT_KBD; /* -k */
 int delay_ms = DEFAULT_DELAY_MS;        /* -d */
 
@@ -78,12 +88,13 @@ void parse_args(int argc, char **argv) {
       }
    }
 
-	while( (opt = getopt(argc, argv, "d:hk:vV")) != -1) {
+	while( (opt = getopt(argc, argv, "d:hfk:vV")) != -1) {
 		switch(opt) {
-			case 'v': debugging++;             break;
 			case 'd': delay_ms = atoi(optarg); break;
-			case 'k': keyboard_dev = optarg;   break;
+			case 'f': foreground++;            break;
 			case 'h': print_help(); exit(0);   break;
+			case 'k': keyboard_dev = optarg;   break;
+			case 'v': debugging++;             break;
 			case 'V': version(); exit(0);      break;
 			case '?': die("invalid option (try --help)"); break;
 			default:  print_help(); exit(1);              break;
@@ -93,6 +104,64 @@ void parse_args(int argc, char **argv) {
 	if(delay_ms < 1) die("invalid -d argument");
 }
 
+/* since every keystroke passes through this daemon, we *don't*
+   want it to be swapped out. it would suck if you couldn't type
+   because you were compiling something huge... note that we have to
+   do this after all the forking, see mlockall(2) for details. */
+void lock_memory(void) {
+	if(mlockall(MCL_CURRENT) >= 0) {
+		debug("mlockall() succeeded");
+	} else {
+		warn("can't lock memory: %s", strerror(errno));
+	}
+}
+
+/* TODO: look into using *actual* realtime scheduling, as
+   described in sched(7). */
+void set_realtime(void) {
+	if(setpriority(PRIO_PROCESS, 0, -20) >= 0) {
+		debug("setpriority() succeeded");
+	} else {
+		warn("can't setpriority(): %s", strerror(errno));
+	}
+}
+
+void drop_privs(void) {
+	const char *user, *group;
+	struct passwd *pw;
+	struct group *gr;
+	gid_t gid;
+
+	user = getenv("MARSON_USER");
+
+	if(!user) user = DEFAULT_USER;
+
+	if( !(pw = getpwnam(user)) ) {
+		die("no such user '%s'", user);
+	}
+
+	if( (group = getenv("MARSON_GROUP")) ) {
+		if( !(gr = getgrnam(user)) ) {
+			die("no such group '%s'", group);
+		}
+		gid = gr->gr_gid;
+	} else {
+		gid = pw->pw_gid;
+	}
+
+	debug("about to drop privileges to user/group %d/%d", pw->pw_uid, gid);
+
+	if(setgid(gid) < 0) {
+		die("can't change group ID to %d: %s", gid, strerror(errno));
+	}
+
+	if(setuid(pw->pw_uid) < 0) {
+		die("can't change user ID to %d: %s", pw->pw_uid, strerror(errno));
+	}
+
+	debug("now running as user/group %d/%d", getuid(), getgid());
+}
+
 void daemonize(void) {
 	int pid;
 
@@ -117,10 +186,28 @@ void daemonize(void) {
 	}
 
 	/* we are the grandchild here */
+
+	/* nothing left to say, close stdin/out/err and cd to / so at
+	   shutdown time, umount won't trip over our cwd. */
 	chdir("/");
 	close(0);
 	close(1);
 	close(2);
+
+	/* nowhere for debug messages to go, so turn it off */
+	debugging = 0;
+
+	lock_memory();
+	set_realtime();
+	drop_privs();
+}
+
+void set_evbit(int outfd, int event) {
+	if(ioctl(outfd, UI_SET_EVBIT, event) >= 0) {
+		debug("UI_SET_EVBIT %d OK");
+	} else {
+		die("UI_SET_EVBIT %d failed: %s", event, strerror(errno));
+	}
 }
 
 int main(int argc, char **argv) {
@@ -151,12 +238,12 @@ int main(int argc, char **argv) {
 		die("failed to grab %s: %s", keyboard_dev, strerror(errno));
 	}
 
-	if(ioctl(outfd, UI_SET_EVBIT, EV_KEY) >= 0) {
-		debug("UI_SET_EVBIT OK");
-	} else {
-		die("UI_SET_EVBIT failed: %s", strerror(errno));
-	}
+	set_evbit(outfd, EV_KEY); /* get and send keystroke events... */
+	set_evbit(outfd, EV_SYN); /* ...sync events... */
+	set_evbit(outfd, EV_MSC); /* ...and miscellaneous. */
+	/* the other event types will never be sent by a keyboard. */
 
+	/* we want all possible keystrokes */
 	for(i = 0; i < KEY_MAX; i++) {
 		if(ioctl(outfd, UI_SET_KEYBIT, i) >= 0) {
 			/* we don't wanna be *that* verbose */
@@ -185,28 +272,47 @@ int main(int argc, char **argv) {
 		die("UI_DEV_CREATE failed: %s", strerror(errno));
 	}
 
-	if(!debugging) daemonize();
 
-	/* note: don't call die() unless debugging is true, since daemonize()
-	   closes our stderr (there's nowhere for the error message to print). */
+	/* this must be done while still running as root... */
+	if(foreground) {
+		lock_memory();
+		set_realtime();
+		drop_privs();
+	} else {
+		daemonize();
+	}
 
+	/* note: don't call debug() or die() unless foreground is true, since
+	   daemonize() closes our stderr (there's nowhere for the messages
+	   to print). */
 	while(1) {
 		if(read(infd, &ev, sizeof(ev)) < 0) {
-			if(debugging)
+			if(foreground) {
 				die("read from %s failed: %s", keyboard_dev, strerror(errno));
+			} else {
+				exit(1);
+			}
 		}
 
-		debug("event: type %d, code %d, value %d\n",
-				ev.type, ev.code, ev.value);
+		if(foreground) {
+			debug("got event: type %d, code %d, value %d\n",
+					ev.type, ev.code, ev.value);
+		}
 
+		/* value == 0 means key release (a 1 would be a press) */
 		if(ev.type == EV_KEY && ev.code == KEY_ENTER && ev.value == 0) {
-			debug("got Enter key release, delaying %d ms", delay_ms);
+			if(foreground) {
+				debug("!!! got Enter key release, delaying %d ms", delay_ms);
+			}
 			usleep(delay_ms * 1000);
 		}
 
 		if(write(outfd, &ev, sizeof(ev)) < 0) {
-			if(debugging)
+			if(foreground) {
 				die("write to /dev/uinput failed: %s", strerror(errno));
+			} else {
+				exit(1);
+			}
 		}
 	}
 
@@ -231,4 +337,8 @@ event: type 0, code 0, value 0
 event: type 4, code 4, value 458792
 event: type 1, code 28, value 0
 event: type 0, code 0, value 0
+
+Onlt the type 1 messages concern us, but we have to pass
+them all through. code 28 is KEY_ENTER, value is 1 for press,
+0 for release.
 */