daemon: fork before threads are spawned

It's not really a good idea to fork after glib has initialized,
since it has helper threads that may have taken locks etc.

This commit forks really early to prevent locks from leaking
and causing deadlock.

Signed-off-by: Cosimo Cecchi <cosimoc@gnome.org>
 * Split out separate function
 * Check return value of g_unix_open_pipe()
 * Don't fork when running foreground
 * Read login password before fork()

Signed-off-by: Stef Walter <stefw@gnome.org>
 * Since stdout is open, just print evironment directly

https://bugzilla.gnome.org/show_bug.cgi?id=756059

1 files changed, 50 insertions, 22 deletions

diff --git a/daemon/gkd-main.c b/daemon/gkd-main.c
index f5676337..af22cfc7 100644
--- a/daemon/gkd-main.c
+++ b/daemon/gkd-main.c
@@ -58,6 +58,8 @@
 #include <sys/stat.h>
 #include <sys/wait.h>
 
+#include <gio/gunixinputstream.h>
+#include <gio/gunixoutputstream.h>
 #include <glib.h>
 #include <glib/gi18n.h>
 #include <glib-object.h>
@@ -125,6 +127,7 @@ static gchar* control_directory = NULL;
 static guint timeout_id = 0;
 static gboolean initialization_completed = FALSE;
 static GMainLoop *loop = NULL;
+static int parent_wakeup_fd = -1;
 
 static GOptionEntry option_entries[] = {
 	{ "start", 's', 0, G_OPTION_ARG_NONE, &run_for_start,
@@ -605,22 +608,43 @@ discover_other_daemon (DiscoverFunc callback, gboolean acquire)
 }
 
 static void
+redirect_fds_after_fork (void)
+{
+	int fd, i;
+
+	for (i = 0; i < 3; ++i) {
+		fd = open ("/dev/null", O_RDONLY);
+		sane_dup2 (fd, i);
+		close (fd);
+	}
+}
+
+static void
+block_on_fd (int fd)
+{
+	unsigned char dummy;
+	read (fd, &dummy, 1);
+}
+
+static int
 fork_and_print_environment (void)
 {
 	int status;
 	pid_t pid;
-	int fd, i;
+	int wakeup_fds[2] = { -1, -1 };
 
 	if (run_foreground) {
-		print_environment ();
-		return;
+		return -1;
 	}
 
+	if (!g_unix_open_pipe (wakeup_fds, FD_CLOEXEC, NULL))
+		exit (1);
+
 	pid = fork ();
 
 	if (pid != 0) {
-
 		/* Here we are in the initial process */
+		close (wakeup_fds[1]);
 
 		if (run_daemonized) {
 
@@ -633,8 +657,8 @@ fork_and_print_environment (void)
 				exit (WEXITSTATUS (status));
 
 		} else {
-			/* Not double forking */
-			print_environment ();
+			/* Not double forking, wait for child */
+			block_on_fd (wakeup_fds[0]);
 		}
 
 		/* The initial process exits successfully */
@@ -654,6 +678,7 @@ fork_and_print_environment (void)
 		pid = fork ();
 
 		if (pid != 0) {
+			close (wakeup_fds[1]);
 
 			/* Here we are in the intermediate child process */
 
@@ -665,7 +690,7 @@ fork_and_print_environment (void)
 				exit (1);
 
 			/* We've done two forks. */
-			print_environment ();
+			block_on_fd (wakeup_fds[0]);
 
 			/* The intermediate child exits */
 			exit (0);
@@ -674,12 +699,7 @@ fork_and_print_environment (void)
 	}
 
 	/* Here we are in the resulting daemon or background process. */
-
-	for (i = 0; i < 3; ++i) {
-		fd = open ("/dev/null", O_RDONLY);
-		sane_dup2 (fd, i);
-		close (fd);
-	}
+	return wakeup_fds[1];
 }
 
 static gboolean
@@ -876,14 +896,23 @@ main (int argc, char *argv[])
 		exit (0);
 	}
 
+	if (perform_unlock) {
+		login_password = read_login_password (STDIN);
+		atexit (clear_login_password);
+	}
+
+	/* The whole forking and daemonizing dance starts here. */
+	parent_wakeup_fd = fork_and_print_environment();
+
 	/* The --start option */
 	if (run_for_start) {
 		if (discover_other_daemon (initialize_daemon_at, TRUE)) {
 			/*
-			 * Another daemon was initialized, print out environment
-			 * for any callers, and quit or go comatose.
+			 * Another daemon was initialized, print out environment,
+			 * tell parent we're done, and quit or go comatose.
 			 */
 			print_environment ();
+			close (parent_wakeup_fd);
 			if (run_foreground)
 				while (sleep(0x08000000) == 0);
 			cleanup_and_exit (0);
@@ -908,11 +937,6 @@ main (int argc, char *argv[])
 	if (!gkd_control_listen ())
 		return FALSE;
 
-	if (perform_unlock) {
-		login_password = read_login_password (STDIN);
-		atexit (clear_login_password);
-	}
-
 	/* The --login option. Delayed initialization */
 	if (run_for_login) {
 		timeout_id = g_timeout_add_seconds (LOGIN_TIMEOUT, (GSourceFunc) on_login_timeout, NULL);
@@ -926,8 +950,12 @@ main (int argc, char *argv[])
 
 	signal (SIGPIPE, SIG_IGN);
 
-	/* The whole forking and daemonizing dance starts here. */
-	fork_and_print_environment();
+	/* Print the environment and tell the parent we're done */
+	print_environment ();
+	close (parent_wakeup_fd);
+
+	if (!run_foreground)
+		redirect_fds_after_fork ();
 
 	g_unix_signal_add (SIGTERM, on_signal_term, loop);
 	g_unix_signal_add (SIGHUP, on_signal_term, loop);