[X.25]: Add call forwarding

Adds call forwarding to X.25, allowing it to operate like an X.25 router.
Useful if one needs to manipulate X.25 traffic with tools like tc.
This is an update/cleanup based off a patch submitted by Daniel Ferenci a few years ago.

Thanks Alan for the feedback.
Added the null check to the clones.
Moved the skb_clone's into the forwarding functions.

Worked ok with Cisco XoT, linux X.25 back to back, and some old NTUs/PADs.

Signed-off-by: Andrew Hendry <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/x25.h

···
 	unsigned long 		vc_facil_mask;	/* inc_call facilities mask */
 };
 
+struct x25_forward {
+	struct list_head	node;
+	unsigned int		lci;
+	struct net_device	*dev1;
+	struct net_device	*dev2;
+	atomic_t		refcnt;
+};
+
 static inline struct x25_sock *x25_sk(const struct sock *sk)
 {
 	return (struct x25_sock *)sk;
···
 				struct x25_facilities *,
 				struct x25_dte_facilities *);
 extern void x25_limit_facilities(struct x25_facilities *, struct x25_neigh *);
+
+/* x25_forward.c */
+extern void x25_clear_forward_by_lci(unsigned int lci);
+extern void x25_clear_forward_by_dev(struct net_device *);
+extern int x25_forward_data(int, struct x25_neigh *, struct sk_buff *);
+extern int x25_forward_call(struct x25_address *, struct x25_neigh *,
+				struct sk_buff *, int);
 
 /* x25_in.c */
 extern int  x25_process_rx_frame(struct sock *, struct sk_buff *);
···
 extern rwlock_t x25_list_lock;
 extern struct list_head x25_route_list;
 extern rwlock_t x25_route_list_lock;
+extern struct list_head x25_forward_list;
+extern rwlock_t x25_forward_list_lock;
 
 extern int x25_proc_init(void);
 extern void x25_proc_exit(void);

net/x25/Makefile

···
 
 x25-y			:= af_x25.o x25_dev.o x25_facilities.o x25_in.o \
 			   x25_link.o x25_out.o x25_route.o x25_subr.o \
-			   x25_timer.o x25_proc.o
+			   x25_timer.o x25_proc.o x25_forward.o
 x25-$(CONFIG_SYSCTL)	+= sysctl_net_x25.o

net/x25/af_x25.c

···
 	struct x25_address source_addr, dest_addr;
 	struct x25_facilities facilities;
 	struct x25_dte_facilities dte_facilities;
-	int len, rc;
+	int len, addr_len, rc;
 
 	/*
 	 *	Remove the LCI and frame type.
···
 	 *	Extract the X.25 addresses and convert them to ASCII strings,
 	 *	and remove them.
 	 */
-	skb_pull(skb, x25_addr_ntoa(skb->data, &source_addr, &dest_addr));
+	addr_len = x25_addr_ntoa(skb->data, &source_addr, &dest_addr);
+	skb_pull(skb, addr_len);
 
 	/*
 	 *	Get the length of the facilities, skip past them for the moment
···
 	sk = x25_find_listener(&source_addr,skb);
 	skb_push(skb,len);
 
+	if (sk != NULL && sk_acceptq_is_full(sk)) {
+		goto out_sock_put;
+	}
+
 	/*
-	 *	We can't accept the Call Request.
+	 *	We dont have any listeners for this incoming call.
+	 *	Try forwarding it.
 	 */
-	if (sk == NULL || sk_acceptq_is_full(sk))
-		goto out_clear_request;
+	if (sk == NULL) {
+		skb_push(skb, addr_len + X25_STD_MIN_LEN);
+		if (x25_forward_call(&dest_addr, nb, skb, lci) > 0)
+		{
+			/* Call was forwarded, dont process it any more */
+			kfree_skb(skb);
+			rc = 1;
+			goto out;
+		} else {
+			/* No listeners, can't forward, clear the call */
+			goto out_clear_request;
+		}
+	}
 
 	/*
 	 *	Try to reach a compromise on the requested facilities.
···
 			x25_disconnect(s, ENETUNREACH, 0, 0);
 
 	write_unlock_bh(&x25_list_lock);
+
+	/* Remove any related forwards */
+	x25_clear_forward_by_dev(nb->dev);
 }
 
 static int __init x25_init(void)

net/x25/x25_dev.c

···
 		return x25_rx_call_request(skb, nb, lci);
 
 	/*
-	 *	Its not a Call Request, nor is it a control frame.
-	 *      Let caller throw it away.
+	 * 	Its not a Call Request, nor is it a control frame.
+	 *	Can we forward it?
 	 */
+
+	if (x25_forward_data(lci, nb, skb)) {
+		if (frametype == X25_CLEAR_CONFIRMATION) {
+			x25_clear_forward_by_lci(lci);
+		}
+		kfree_skb(skb);
+		return 1;
+	}
+
 /*
 	x25_transmit_clear_request(nb, lci, 0x0D);
 */

net/x25/x25_forward.c

···
+/*
+ *	This module:
+ *		This module is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ *	History
+ *	03-01-2007	Added forwarding for x.25	Andrew Hendry
+ */
+#include <linux/if_arp.h>
+#include <linux/init.h>
+#include <net/x25.h>
+
+struct list_head x25_forward_list = LIST_HEAD_INIT(x25_forward_list);
+DEFINE_RWLOCK(x25_forward_list_lock);
+
+int x25_forward_call(struct x25_address *dest_addr, struct x25_neigh *from,
+			struct sk_buff *skb, int lci)
+{
+	struct x25_route *rt;
+	struct x25_neigh *neigh_new = NULL;
+	struct list_head *entry;
+	struct x25_forward *x25_frwd, *new_frwd;
+	struct sk_buff *skbn;
+	short same_lci = 0;
+	int rc = 0;
+
+	if ((rt = x25_get_route(dest_addr)) != NULL) {
+
+		if ((neigh_new = x25_get_neigh(rt->dev)) == NULL) {
+			/* This shouldnt happen, if it occurs somehow
+			 * do something sensible
+			 */
+			goto out_put_route;
+		}
+
+		/* Avoid a loop. This is the normal exit path for a
+		 * system with only one x.25 iface and default route
+		 */
+		if (rt->dev == from->dev) {
+			goto out_put_nb;
+		}
+
+		/* Remote end sending a call request on an already
+		 * established LCI? It shouldnt happen, just in case..
+		 */
+		read_lock_bh(&x25_forward_list_lock);
+		list_for_each(entry, &x25_forward_list) {
+			x25_frwd = list_entry(entry, struct x25_forward, node);
+			if (x25_frwd->lci == lci) {
+				printk(KERN_WARNING "X.25: call request for lci which is already registered!, transmitting but not registering new pair\n");
+				same_lci = 1;
+			}
+		}
+		read_unlock_bh(&x25_forward_list_lock);
+
+		/* Save the forwarding details for future traffic */
+		if (!same_lci){
+			if ((new_frwd = kmalloc(sizeof(struct x25_forward),
+							GFP_ATOMIC)) == NULL){
+				rc = -ENOMEM;
+				goto out_put_nb;
+			}
+			new_frwd->lci = lci;
+			new_frwd->dev1 = rt->dev;
+			new_frwd->dev2 = from->dev;
+			write_lock_bh(&x25_forward_list_lock);
+			list_add(&new_frwd->node, &x25_forward_list);
+			write_unlock_bh(&x25_forward_list_lock);
+		}
+
+		/* Forward the call request */
+		if ( (skbn = skb_clone(skb, GFP_ATOMIC)) == NULL){
+			goto out_put_nb;
+		}
+		x25_transmit_link(skbn, neigh_new);
+		rc = 1;
+	}
+
+
+out_put_nb:
+	x25_neigh_put(neigh_new);
+
+out_put_route:
+	x25_route_put(rt);
+	return rc;
+}
+
+
+int x25_forward_data(int lci, struct x25_neigh *from, struct sk_buff *skb) {
+
+	struct x25_forward *frwd;
+	struct list_head *entry;
+	struct net_device *peer = NULL;
+	struct x25_neigh *nb;
+	struct sk_buff *skbn;
+	int rc = 0;
+
+	read_lock_bh(&x25_forward_list_lock);
+	list_for_each(entry, &x25_forward_list) {
+		frwd = list_entry(entry, struct x25_forward, node);
+		if (frwd->lci == lci) {
+			/* The call is established, either side can send */
+			if (from->dev == frwd->dev1) {
+				peer = frwd->dev2;
+			} else {
+				peer = frwd->dev1;
+			}
+			break;
+		}
+	}
+	read_unlock_bh(&x25_forward_list_lock);
+
+	if ( (nb = x25_get_neigh(peer)) == NULL)
+		goto out;
+
+	if ( (skbn = pskb_copy(skb, GFP_ATOMIC)) == NULL){
+		goto out;
+
+	}
+	x25_transmit_link(skbn, nb);
+
+	x25_neigh_put(nb);
+	rc = 1;
+out:
+	return rc;
+}
+
+void x25_clear_forward_by_lci(unsigned int lci)
+{
+	struct x25_forward *fwd;
+	struct list_head *entry, *tmp;
+
+	write_lock_bh(&x25_forward_list_lock);
+
+	list_for_each_safe(entry, tmp, &x25_forward_list) {
+		fwd = list_entry(entry, struct x25_forward, node);
+		if (fwd->lci == lci) {
+			list_del(&fwd->node);
+			kfree(fwd);
+		}
+	}
+	write_unlock_bh(&x25_forward_list_lock);
+}
+
+
+void x25_clear_forward_by_dev(struct net_device *dev)
+{
+	struct x25_forward *fwd;
+	struct list_head *entry, *tmp;
+
+	write_lock_bh(&x25_forward_list_lock);
+
+	list_for_each_safe(entry, tmp, &x25_forward_list) {
+		fwd = list_entry(entry, struct x25_forward, node);
+		if ((fwd->dev1 == dev) || (fwd->dev2 == dev)){
+			list_del(&fwd->node);
+			kfree(fwd);
+		}
+	}
+	write_unlock_bh(&x25_forward_list_lock);
+}

net/x25/x25_route.c

···
 			__x25_remove_route(rt);
 	}
 	write_unlock_bh(&x25_route_list_lock);
+
+	/* Remove any related forwarding */
+	x25_clear_forward_by_dev(dev);
 }
 
 /*