Invoke revoke(2) on the slave pty in the pts(4) case (new_openpty()) to

kick off any other users on the device line before using it since
openpty(3) is documented to do this.  Note that grantpt(3) does not
call revoke(2), it only adjusts permissions and ownership.

MFC after:	3 days

1 files changed, 13 insertions, 1 deletions

diff --git a/lib/libutil/pty.c b/lib/libutil/pty.c
index c94ce99..1fe8be2 100644
--- a/lib/libutil/pty.c
+++ b/lib/libutil/pty.c
@@ -55,6 +55,7 @@ static int
 new_openpty(int *amaster, int *aslave, char *name, struct termios *termp,
     struct winsize *winp)
 {
+	const char *slavename;
 	int master, slave;
 
 	master = posix_openpt(O_RDWR);
@@ -66,7 +67,18 @@ new_openpty(int *amaster, int *aslave, char *name, struct termios *termp,
 		return (-1);
 	}
 
-	slave = open(ptsname(master), O_RDWR);
+	slavename = ptsname(master);
+	if (slavename == NULL) {
+		close(master);
+		return (-1);
+	}
+
+	if (revoke(slavename) == -1) {
+		close(master);
+		return (-1);
+	}
+
+	slave = open(slavename, O_RDWR);
 	if (slave == -1) {
 		close(master);
 		return (-1);