[PATCH] n_tty: add null check for tty->link in packet mode

[Osama Abdelkader]

Add null check for tty->link before dereferencing in n_tty_read and
n_tty_poll. When the pty master closes, tty->link can be NULL while
the slave is still reading, causing a null pointer dereference.

Signed-off-by: Osama Abdelkader <osama.abdelkader@xxxxxxxxx>
---
 drivers/tty/n_tty.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index e6a0f5b40d0a..dc04b87364f6 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2232,7 +2232,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, u8 *kbuf,
 	add_wait_queue(&tty->read_wait, &wait);
 	while (nr) {
 		/* First test for status change. */
-		if (packet && tty->link->ctrl.pktstatus) {
+		if (packet && tty->link && tty->link->ctrl.pktstatus) {
 			u8 cs;
 			if (kb != kbuf)
 				break;
@@ -2444,7 +2444,7 @@ static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
 		if (input_available_p(tty, 1))
 			mask |= EPOLLIN | EPOLLRDNORM;
 	}
-	if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
+	if (tty->ctrl.packet && tty->link && tty->link->ctrl.pktstatus)
 		mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 		mask |= EPOLLHUP;
-- 
2.43.0