Open /dev/ptm before pledge() and save it to be used for PTMGET later

(this means inlining forkpty()).

ok deraadt

Makefile

@@ -97,6 +97,7 @@ SRCS=	alerts.c \
 	paste.c \
 	proc.c \
 	procname.c \
+	pty.c \
 	resize.c \
 	screen-redraw.c \
 	screen-write.c \

client.c

@@ -303,6 +303,8 @@ client_main(struct event_base *base, int argc, char **argv, int flags,
 		fatal("pledge failed");
 
 	/* Free stuff that is not used in the client. */
+	if (ptm_fd != -1)
+		close(ptm_fd);
 	options_free(global_options);
 	options_free(global_s_options);
 	options_free(global_w_options);

pty.c

@@ -0,0 +1,67 @@
+/* $OpenBSD$ */
+
+/*
+ * Copyright (c) 2017 Nicholas Marriott <nicholas.marriott@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/ioctl.h>
+#include <sys/time.h>
+#include <sys/tty.h>
+
+#include <fcntl.h>
+#include <string.h>
+#include <termios.h>
+#include <unistd.h>
+#include <util.h>
+
+int	pty_open(int *);
+pid_t	pty_fork(int, int *, char *, size_t, struct winsize *);
+
+int
+pty_open(int *fd)
+{
+	*fd = open(PATH_PTMDEV, O_RDWR|O_CLOEXEC);
+	if (*fd < 0)
+	    return (-1);
+	return (0);
+}
+
+pid_t
+pty_fork(int ptmfd, int *fd, char *name, size_t namelen, struct winsize *ws)
+{
+	struct ptmget	ptm;
+	pid_t		pid;
+
+	if ((ioctl(ptmfd, PTMGET, &ptm) == -1))
+		return (-1);
+
+	strlcpy(name, ptm.sn, namelen);
+	ioctl(ptm.sfd, TIOCSWINSZ, ws);
+
+	switch (pid = fork()) {
+	case -1:
+		close(ptm.cfd);
+		close(ptm.sfd);
+		return (-1);
+	case 0:
+		close(ptm.cfd);
+		login_tty(ptm.sfd);
+		return (0);
+	}
+	*fd = ptm.cfd;
+	close(ptm.sfd);
+	return (pid);
+}

tmux.c

@@ -43,6 +43,7 @@ struct hooks	*global_hooks;
 
 struct timeval	 start_time;
 const char	*socket_path;
+int		 ptm_fd = -1;
 
 static __dead void	 usage(void);
 static char		*make_label(const char *);
@@ -258,6 +259,8 @@ main(int argc, char **argv)
 	if (shellcmd != NULL && argc != 0)
 		usage();
 
+	if (pty_open(&ptm_fd) != 0)
+		errx(1, "open(\"/dev/ptm\"");
 	if (pledge("stdio rpath wpath cpath flock fattr unix getpw sendfd "
 	    "recvfd proc exec tty ps", NULL) != 0)
 		err(1, "pledge");

tmux.h

@@ -1501,6 +1501,7 @@ extern struct options	*global_w_options;
 extern struct environ	*global_environ;
 extern struct timeval	 start_time;
 extern const char	*socket_path;
+extern int		 ptm_fd;
 int		 areshell(const char *);
 void		 setblocking(int, int);
 const char	*find_home(void);
@@ -2329,4 +2330,8 @@ void		 style_apply_update(struct grid_cell *, struct options *,
 int		 style_equal(const struct grid_cell *,
 		     const struct grid_cell *);
 
+/* pty.c */
+int		 pty_open(int *);
+pid_t		 pty_fork(int, int *, char *, size_t, struct winsize *);
+
 #endif /* TMUX_H */

window.c

@@ -886,7 +886,7 @@ 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);
 
-	switch (wp->pid = forkpty(&wp->fd, wp->tty, NULL, &ws)) {
+	switch (wp->pid = pty_fork(ptm_fd, &wp->fd, wp->tty, sizeof wp->tty, &ws)) {
 	case -1:
 		wp->fd = -1;
 		xasprintf(cause, "%s: %s", cmd, strerror(errno));