[PATCH] 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 netdev_alloc_skb() would allocate an
skb, but if ser or ser->dev was NULL, the function would return early
without freeing the allocated skb. Additionally, ser->dev was accessed
before checking if it was NULL, which could cause a NULL pointer
dereference.

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>
---
 drivers/net/caif/caif_serial.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index c398ac42eae9..0ec9670bd35c 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -152,12 +152,16 @@ static void ldisc_receive(struct tty_struct *tty, const u8 *data,
 	int ret;
 
 	ser = tty->disc_data;
+	if (!ser)
+		return;
 
 	/*
 	 * NOTE: flags may contain information about break or overrun.
 	 * This is not yet handled.
 	 */
 
+	if (!ser->dev)
+		return;
 
 	/*
 	 * Workaround for garbage at start of transmission,
@@ -170,8 +174,6 @@ 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)
-- 
2.43.0