[PATCH v2] net: caif: fix memory leak in ldisc_receive

[Osama Abdelkader]

Add NULL pointer checks for ser and ser->dev in ldisc_receive() to
prevent memory leaks when the function is called during device close
or in race conditions where tty->disc_data or ser->dev may be NULL.

The memory leak occurred because ser->dev was accessed before checking
if ser or ser->dev was NULL, which could cause a NULL pointer
dereference or use of freed memory. Additionally, set tty->disc_data
to NULL in ldisc_close() to prevent receive_buf() from using a freed
ser pointer after the line discipline is closed.

Reported-by: syzbot+f9d847b2b84164fa69f3@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=f9d847b2b84164fa69f3
Fixes: 9b27105b4a44 ("net-caif-driver: add CAIF serial driver (ldisc)")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Osama Abdelkader <osama.abdelkader@xxxxxxxxx>
---
v2:
1.Combine NULL pointer checks for ser and ser->dev in ldisc_receive()
2.Set tty->disc_data = NULL in ldisc_close() to prevent receive_buf()
from using a freed ser pointer after close.
3.Add NULL pointer check for ser in ldisc_close()
---
 drivers/net/caif/caif_serial.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index c398ac42eae9..970237a3ccca 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -152,6 +152,8 @@ static void ldisc_receive(struct tty_struct *tty, const u8 *data,
 	int ret;
 
 	ser = tty->disc_data;
+	if (!ser || !ser->dev)
+		return;
 
 	/*
 	 * NOTE: flags may contain information about break or overrun.
@@ -170,8 +172,6 @@ static void ldisc_receive(struct tty_struct *tty, const u8 *data,
 		return;
 	}
 
-	BUG_ON(ser->dev == NULL);
-
 	/* Get a suitable caif packet and copy in data. */
 	skb = netdev_alloc_skb(ser->dev, count+1);
 	if (skb == NULL)
@@ -355,11 +355,15 @@ static void ldisc_close(struct tty_struct *tty)
 {
 	struct ser_device *ser = tty->disc_data;
 
+	if (!ser)
+		return;
+
 	tty_kref_put(ser->tty);
 
 	spin_lock(&ser_lock);
 	list_move(&ser->node, &ser_release_list);
 	spin_unlock(&ser_lock);
+	tty->disc_data = NULL;
 	schedule_work(&ser_release_work);
 }
 
-- 
2.43.0