net: rose: convert 'use' field to refcount_t

The 'use' field in struct rose_neigh is used as a reference counter but
lacks atomicity. This can lead to race conditions where a rose_neigh
structure is freed while still being referenced by other code paths.

For example, when rose_neigh->use becomes zero during an ioctl operation
via rose_rt_ioctl(), the structure may be removed while its timer is
still active, potentially causing use-after-free issues.

This patch changes the type of 'use' from unsigned short to refcount_t and
updates all code paths to use rose_neigh_hold() and rose_neigh_put() which
operate reference counts atomically.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Takamitsu Iwai <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/rose.h

···
 #ifndef _ROSE_H
 #define _ROSE_H 
 
+#include <linux/refcount.h>
 #include <linux/rose.h>
 #include <net/ax25.h>
 #include <net/sock.h>
···
 	ax25_cb			*ax25;
 	struct net_device		*dev;
 	unsigned short		count;
-	unsigned short		use;
+	refcount_t		use;
 	unsigned int		number;
 	char			restarted;
 	char			dce_mode;
···
 
 #define rose_sk(sk) ((struct rose_sock *)(sk))
 
+static inline void rose_neigh_hold(struct rose_neigh *rose_neigh)
+{
+	refcount_inc(&rose_neigh->use);
+}
+
 static inline void rose_neigh_put(struct rose_neigh *rose_neigh)
 {
-	if (rose_neigh->ax25)
-		ax25_cb_put(rose_neigh->ax25);
-	kfree(rose_neigh->digipeat);
-	kfree(rose_neigh);
+	if (refcount_dec_and_test(&rose_neigh->use)) {
+		if (rose_neigh->ax25)
+			ax25_cb_put(rose_neigh->ax25);
+		kfree(rose_neigh->digipeat);
+		kfree(rose_neigh);
+	}
 }
 
 /* af_rose.c */

net/rose/af_rose.c

···
 
 		if (rose->neighbour == neigh) {
 			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
-			rose->neighbour->use--;
+			rose_neigh_put(rose->neighbour);
 			rose->neighbour = NULL;
 		}
 	}
···
 		if (rose->device == dev) {
 			rose_disconnect(sk, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
 			if (rose->neighbour)
-				rose->neighbour->use--;
+				rose_neigh_put(rose->neighbour);
 			netdev_put(rose->device, &rose->dev_tracker);
 			rose->device = NULL;
 		}
···
 		break;
 
 	case ROSE_STATE_2:
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		release_sock(sk);
 		rose_disconnect(sk, 0, -1, -1);
 		lock_sock(sk);
···
 	rose->lci = rose_new_lci(rose->neighbour);
 	if (!rose->lci) {
 		err = -ENETUNREACH;
+		rose_neigh_put(rose->neighbour);
 		goto out_release;
 	}
 
···
 		dev = rose_dev_first();
 		if (!dev) {
 			err = -ENETUNREACH;
+			rose_neigh_put(rose->neighbour);
 			goto out_release;
 		}
 
 		user = ax25_findbyuid(current_euid());
 		if (!user) {
 			err = -EINVAL;
+			rose_neigh_put(rose->neighbour);
 			dev_put(dev);
 			goto out_release;
 		}
···
 	sk->sk_state     = TCP_SYN_SENT;
 
 	rose->state = ROSE_STATE_1;
-
-	rose->neighbour->use++;
 
 	rose_write_internal(sk, ROSE_CALL_REQUEST);
 	rose_start_heartbeat(sk);
···
 			     GFP_ATOMIC);
 	make_rose->facilities    = facilities;
 
-	make_rose->neighbour->use++;
+	rose_neigh_hold(make_rose->neighbour);
 
 	if (rose_sk(sk)->defer) {
 		make_rose->state = ROSE_STATE_5;

net/rose/rose_in.c

···
 	case ROSE_CLEAR_REQUEST:
 		rose_write_internal(sk, ROSE_CLEAR_CONFIRMATION);
 		rose_disconnect(sk, ECONNREFUSED, skb->data[3], skb->data[4]);
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		break;
 
 	default:
···
 	case ROSE_CLEAR_REQUEST:
 		rose_write_internal(sk, ROSE_CLEAR_CONFIRMATION);
 		rose_disconnect(sk, 0, skb->data[3], skb->data[4]);
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		break;
 
 	case ROSE_CLEAR_CONFIRMATION:
 		rose_disconnect(sk, 0, -1, -1);
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		break;
 
 	default:
···
 	case ROSE_CLEAR_REQUEST:
 		rose_write_internal(sk, ROSE_CLEAR_CONFIRMATION);
 		rose_disconnect(sk, 0, skb->data[3], skb->data[4]);
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		break;
 
 	case ROSE_RR:
···
 	case ROSE_CLEAR_REQUEST:
 		rose_write_internal(sk, ROSE_CLEAR_CONFIRMATION);
 		rose_disconnect(sk, 0, skb->data[3], skb->data[4]);
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		break;
 
 	default:
···
 	if (frametype == ROSE_CLEAR_REQUEST) {
 		rose_write_internal(sk, ROSE_CLEAR_CONFIRMATION);
 		rose_disconnect(sk, 0, skb->data[3], skb->data[4]);
-		rose_sk(sk)->neighbour->use--;
+		rose_neigh_put(rose_sk(sk)->neighbour);
 	}
 
 	return 0;

net/rose/rose_route.c

···
 		rose_neigh->ax25      = NULL;
 		rose_neigh->dev       = dev;
 		rose_neigh->count     = 0;
-		rose_neigh->use       = 0;
 		rose_neigh->dce_mode  = 0;
 		rose_neigh->loopback  = 0;
 		rose_neigh->number    = rose_neigh_no++;
 		rose_neigh->restarted = 0;
+		refcount_set(&rose_neigh->use, 1);
 
 		skb_queue_head_init(&rose_neigh->queue);
 
···
 	struct rose_route *s;
 
 	if (rose_route->neigh1 != NULL)
-		rose_route->neigh1->use--;
+		rose_neigh_put(rose_route->neigh1);
 
 	if (rose_route->neigh2 != NULL)
-		rose_route->neigh2->use--;
+		rose_neigh_put(rose_route->neigh2);
 
 	if ((s = rose_route_list) == rose_route) {
 		rose_route_list = rose_route->next;
···
 		if (rose_node->neighbour[i] == rose_neigh) {
 			rose_neigh->count--;
 
-			if (rose_neigh->count == 0 && rose_neigh->use == 0) {
+			if (rose_neigh->count == 0) {
 				rose_remove_neigh(rose_neigh);
 				rose_neigh_put(rose_neigh);
 			}
···
 	sn->ax25      = NULL;
 	sn->dev       = NULL;
 	sn->count     = 0;
-	sn->use       = 0;
 	sn->dce_mode  = 1;
 	sn->loopback  = 1;
 	sn->number    = rose_neigh_no++;
 	sn->restarted = 1;
+	refcount_set(&sn->use, 1);
 
 	skb_queue_head_init(&sn->queue);
 
···
 		s          = rose_neigh;
 		rose_neigh = rose_neigh->next;
 
-		if (s->use == 0 && !s->loopback) {
-			s->count = 0;
+		if (!s->loopback) {
 			rose_remove_neigh(s);
 			rose_neigh_put(s);
 		}
···
 			for (i = 0; i < node->count; i++) {
 				if (node->neighbour[i]->restarted) {
 					res = node->neighbour[i];
+					rose_neigh_hold(node->neighbour[i]);
 					goto out;
 				}
 			}
···
 				for (i = 0; i < node->count; i++) {
 					if (!rose_ftimer_running(node->neighbour[i])) {
 						res = node->neighbour[i];
+						rose_neigh_hold(node->neighbour[i]);
 						goto out;
 					}
 					failed = 1;
···
 		}
 
 		if (rose_route->neigh1 == rose_neigh) {
-			rose_route->neigh1->use--;
+			rose_neigh_put(rose_route->neigh1);
 			rose_route->neigh1 = NULL;
 			rose_transmit_clear_request(rose_route->neigh2, rose_route->lci2, ROSE_OUT_OF_ORDER, 0);
 		}
 
 		if (rose_route->neigh2 == rose_neigh) {
-			rose_route->neigh2->use--;
+			rose_neigh_put(rose_route->neigh2);
 			rose_route->neigh2 = NULL;
 			rose_transmit_clear_request(rose_route->neigh1, rose_route->lci1, ROSE_OUT_OF_ORDER, 0);
 		}
···
 			rose_clear_queues(sk);
 			rose->cause	 = ROSE_NETWORK_CONGESTION;
 			rose->diagnostic = 0;
-			rose->neighbour->use--;
+			rose_neigh_put(rose->neighbour);
 			rose->neighbour	 = NULL;
 			rose->lci	 = 0;
 			rose->state	 = ROSE_STATE_0;
···
 
 	if ((new_lci = rose_new_lci(new_neigh)) == 0) {
 		rose_transmit_clear_request(rose_neigh, lci, ROSE_NETWORK_CONGESTION, 71);
-		goto out;
+		goto put_neigh;
 	}
 
 	if ((rose_route = kmalloc(sizeof(*rose_route), GFP_ATOMIC)) == NULL) {
 		rose_transmit_clear_request(rose_neigh, lci, ROSE_NETWORK_CONGESTION, 120);
-		goto out;
+		goto put_neigh;
 	}
 
 	rose_route->lci1      = lci;
···
 	rose_route->lci2      = new_lci;
 	rose_route->neigh2    = new_neigh;
 
-	rose_route->neigh1->use++;
-	rose_route->neigh2->use++;
+	rose_neigh_hold(rose_route->neigh1);
+	rose_neigh_hold(rose_route->neigh2);
 
 	rose_route->next = rose_route_list;
 	rose_route_list  = rose_route;
···
 	rose_transmit_link(skb, rose_route->neigh2);
 	res = 1;
 
+put_neigh:
+	rose_neigh_put(new_neigh);
 out:
 	spin_unlock_bh(&rose_route_list_lock);
 	spin_unlock_bh(&rose_neigh_list_lock);
···
 			   (rose_neigh->loopback) ? "RSLOOP-0" : ax2asc(buf, &rose_neigh->callsign),
 			   rose_neigh->dev ? rose_neigh->dev->name : "???",
 			   rose_neigh->count,
-			   rose_neigh->use,
+			   refcount_read(&rose_neigh->use) - 1,
 			   (rose_neigh->dce_mode) ? "DCE" : "DTE",
 			   (rose_neigh->restarted) ? "yes" : "no",
 			   ax25_display_timer(&rose_neigh->t0timer) / HZ,

net/rose/rose_timer.c

···
 		break;
 
 	case ROSE_STATE_2:	/* T3 */
-		rose->neighbour->use--;
+		rose_neigh_put(rose->neighbour);
 		rose_disconnect(sk, ETIMEDOUT, -1, -1);
 		break;