netrom: fix a memory leak in nr_rx_frame()

BugLink: https://bugs.launchpad.net/bugs/1840081

[ Upstream commit c8c8218e ]

When the skb is associated with a new sock, just assigning
it to skb->sk is not sufficient, we have to set its destructor
to free the sock properly too.

Reported-by: syzbot+d6636a36d3c34bd88938@syzkaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/netrom/af_netrom.c

@@ -870,7 +870,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 	unsigned short frametype, flags, window, timeout;
 	int ret;
 
-	skb->sk = NULL;		/* Initially we don't know who it's for */
+	skb_orphan(skb);
 
 	/*
 	 *	skb->data points to the netrom frame start
@@ -969,6 +969,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 	window = skb->data[20];
 
 	skb->sk             = make;
+	skb->destructor     = sock_efree;
 	make->sk_state	    = TCP_ESTABLISHED;
 
 	/* Fill in his circuit details */