Close two different races with concurrent opens of pty master devices

that could result in leaked ttys or a leaked pty + tty pair.

MFC after:	1 week

1 files changed, 24 insertions, 5 deletions

diff --git a/sys/kern/tty_pty.c b/sys/kern/tty_pty.c
index 5d28fe6..3827e82 100644
--- a/sys/kern/tty_pty.c
+++ b/sys/kern/tty_pty.c
@@ -100,6 +100,9 @@ static struct cdevsw ptc_cdevsw = {
 	.d_flags =	D_TTY | D_NEEDGIANT,
 };
 
+static struct mtx ptyinit_lock;
+MTX_SYSINIT(ptyinit_lock, &ptyinit_lock, "ptyinit", MTX_DEF);
+
 #define BUFSIZ 100		/* Chunk size iomoved to/from user */
 
 struct	ptsc {
@@ -151,8 +154,16 @@ ptyinit(struct cdev *devc, struct thread *td)
 
 	pt->pt_tty = ttyalloc();
 	pt->pt_tty->t_sc = pt;
-	devc->si_drv1 = pt;
-	devc->si_tty = pt->pt_tty;
+	mtx_lock(&ptyinit_lock);
+	if (devc->si_drv1 == NULL) {
+		devc->si_drv1 = pt;
+		devc->si_tty = pt->pt_tty;
+		mtx_unlock(&ptyinit_lock);
+	} else {
+		mtx_unlock(&ptyinit_lock);
+		ttyrel(pt->pt_tty);
+		free(pt, M_PTY);
+	}
 	return (devc);
 }
 
@@ -335,9 +346,17 @@ ptcopen(struct cdev *dev, int flag, int devtype, struct thread *td)
 	 * we need to recreate it.
 	 */
 	if (pt->pt_tty == NULL) {
-		pt->pt_tty = ttyalloc();
-		pt->pt_tty->t_sc = pt;
-		dev->si_tty = pt->pt_tty;
+		tp = ttyalloc();
+		mtx_lock(&ptyinit_lock);
+		if (pt->pt_tty == NULL) {
+			pt->pt_tty = tp;
+			pt->pt_tty->t_sc = pt;
+			dev->si_tty = pt->pt_tty;
+			mtx_unlock(&ptyinit_lock);
+		} else {
+			mtx_unlock(&ptyinit_lock);
+			ttyrel(tp);
+		}
 	}
 	tp = dev->si_tty;