Block signals between forking and clearing signal handlers (or calling

event_reinit) - if the child gets a signal and fires the libevent signal
handler during this period it could write a signal into the parent's
signal pipe. GitHub issue 1001 from Aaron van Geffen.

cmd-pipe-pane.c

@@ -22,6 +22,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <paths.h>
+#include <signal.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
@@ -62,6 +63,7 @@ cmd_pipe_pane_exec(struct cmd *self, struct cmdq_item *item)
 	char			*cmd;
 	int			 old_fd, pipe_fd[2], null_fd;
 	struct format_tree	*ft;
+	sigset_t		 set, oldset;
 
 	/* Destroy the old pipe. */
 	old_fd = wp->pipe_fd;
@@ -102,16 +104,20 @@ cmd_pipe_pane_exec(struct cmd *self, struct cmdq_item *item)
 	format_free(ft);
 
 	/* Fork the child. */
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &oldset);
 	switch (fork()) {
 	case -1:
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 		cmdq_error(item, "fork error: %s", strerror(errno));
 
 		free(cmd);
 		return (CMD_RETURN_ERROR);
 	case 0:
 		/* Child process. */
-		close(pipe_fd[0]);
 		proc_clear_signals(server_proc);
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
+		close(pipe_fd[0]);
 
 		if (dup2(pipe_fd[1], STDIN_FILENO) == -1)
 			_exit(1);
@@ -132,6 +138,7 @@ cmd_pipe_pane_exec(struct cmd *self, struct cmdq_item *item)
 		_exit(1);
 	default:
 		/* Parent process. */
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 		close(pipe_fd[1]);
 
 		wp->pipe_fd = pipe_fd[0];

job.c

@@ -51,6 +51,7 @@ job_run(const char *cmd, struct session *s, const char *cwd,
 	pid_t		 pid;
 	int		 nullfd, out[2];
 	const char	*home;
+	sigset_t	 set, oldset;
 
 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, out) != 0)
 		return (NULL);
@@ -61,14 +62,18 @@ job_run(const char *cmd, struct session *s, const char *cwd,
 	 */
 	env = environ_for_session(s, !cfg_finished);
 
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &oldset);
 	switch (pid = fork()) {
 	case -1:
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 		environ_free(env);
 		close(out[0]);
 		close(out[1]);
 		return (NULL);
-	case 0:		/* child */
+	case 0:
 		proc_clear_signals(server_proc);
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 
 		if (cwd == NULL || chdir(cwd) != 0) {
 			if ((home = find_home()) == NULL || chdir(home) != 0)
@@ -100,7 +105,7 @@ job_run(const char *cmd, struct session *s, const char *cwd,
 		fatal("execl failed");
 	}
 
-	/* parent */
+	sigprocmask(SIG_SETMASK, &oldset, NULL);
 	environ_free(env);
 	close(out[1]);
 

server.c

@@ -141,21 +141,24 @@ server_start(struct tmuxproc *client, struct event_base *base, int lockfd,
 {
 	int		 pair[2];
 	struct job	*job;
+	sigset_t	 set, oldset;
 
 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
 		fatal("socketpair failed");
 
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &oldset);
 	switch (fork()) {
 	case -1:
 		fatal("fork failed");
 	case 0:
 		break;
 	default:
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 		close(pair[1]);
 		return (pair[0]);
 	}
 	close(pair[0]);
-
 	if (daemon(1, 0) != 0)
 		fatal("daemon failed");
 	proc_clear_signals(client);
@@ -163,6 +166,7 @@ server_start(struct tmuxproc *client, struct event_base *base, int lockfd,
 		fatalx("event_reinit failed");
 	server_proc = proc_start("server");
 	proc_set_signals(server_proc, server_signal);
+	sigprocmask(SIG_SETMASK, &oldset, NULL);
 
 	if (log_get_level() > 1)
 		tty_create_log();

window.c

@@ -22,6 +22,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <fnmatch.h>
+#include <signal.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
@@ -886,6 +887,7 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 	const char	*ptr, *first, *home;
 	struct termios	 tio2;
 	int		 i;
+	sigset_t	 set, oldset;
 
 	if (wp->fd != -1) {
 		bufferevent_free(wp->event);
@@ -915,14 +917,21 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 	ws.ws_col = screen_size_x(&wp->base);
 	ws.ws_row = screen_size_y(&wp->base);
 
-	wp->pid = fdforkpty(ptm_fd, &wp->fd, wp->tty, NULL, &ws);
-	switch (wp->pid) {
+	sigfillset(&set);
+	sigprocmask(SIG_BLOCK, &set, &oldset);
+	switch (wp->pid = fdforkpty(ptm_fd, &wp->fd, wp->tty, NULL, &ws)) {
 	case -1:
 		wp->fd = -1;
+
 		xasprintf(cause, "%s: %s", cmd, strerror(errno));
 		free(cmd);
+
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
 		return (-1);
 	case 0:
+		proc_clear_signals(server_proc);
+		sigprocmask(SIG_SETMASK, &oldset, NULL);
+
 		if (chdir(wp->cwd) != 0) {
 			if ((home = find_home()) == NULL || chdir(home) != 0)
 				chdir("/");
@@ -936,6 +945,7 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 		if (tcsetattr(STDIN_FILENO, TCSANOW, &tio2) != 0)
 			fatal("tcgetattr failed");
 
+		log_close();
 		closefrom(STDERR_FILENO + 1);
 
 		if (path != NULL)
@@ -943,9 +953,6 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 		environ_set(env, "TMUX_PANE", "%%%u", wp->id);
 		environ_push(env);
 
-		proc_clear_signals(server_proc);
-		log_close();
-
 		setenv("SHELL", wp->shell, 1);
 		ptr = strrchr(wp->shell, '/');
 
@@ -978,6 +985,7 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 		fatal("execl failed");
 	}
 
+	sigprocmask(SIG_SETMASK, &oldset, NULL);
 	setblocking(wp->fd, 0);
 
 	wp->event = bufferevent_new(wp->fd, window_pane_read_callback, NULL,