net: af_can: do not leave a dangling sk pointer in can_create()

On error can_create() frees the allocated sk object, but sock_init_data()
has already attached it to the provided sock object. This will leave a
dangling sk pointer in the sock object and may cause use-after-free later.

Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://patch.msgid.link/20241014153808.51894-5-ignat@cloudflare.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/can/af_can.c

@@ -171,6 +171,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
 		/* release sk on errors */
 		sock_orphan(sk);
 		sock_put(sk);
+		sock->sk = NULL;
 	}
 
  errout: