Current implementation maintains two separate reference counting
mechanisms: the 'count' field in struct rose_neigh tracks references from
rose_node structures, while the 'use' field (now refcount_t) tracks
references from rose_sock.

This patch merges these two reference counting systems using 'use' field
for proper reference management. Specifically, this patch adds incrementing
and decrementing of rose_neigh->use when rose_neigh->count is incremented
or decremented.

This patch also modifies rose_rt_free(), rose_rt_device_down() and
rose_clear_route() to properly release references to rose_neigh objects
before freeing a rose_node through rose_remove_node().

These changes ensure rose_neigh structures are properly freed only when
all references, including those from rose_node structures, are released.
As a result, this resolves a slab-use-after-free issue reported by Syzbot.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+942297eecf7d2d61d1f1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=942297eecf7d2d61d1f1
Signed-off-by: Takamitsu Iwai <takamitz@amazon.co.jp>
---
 net/rose/rose_route.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index a032543bbbc8..20e772114a39 100644
--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -178,6 +178,7 @@ static int __must_check rose_add_node(struct rose_route_struct *rose_route,
 			}
 		}
 		rose_neigh->count++;
+		rose_neigh_hold(rose_neigh);
 
 		goto out;
 	}
@@ -187,6 +188,7 @@ static int __must_check rose_add_node(struct rose_route_struct *rose_route,
 		rose_node->neighbour[rose_node->count] = rose_neigh;
 		rose_node->count++;
 		rose_neigh->count++;
+		rose_neigh_hold(rose_neigh);
 	}
 
 out:
@@ -322,6 +324,7 @@ static int rose_del_node(struct rose_route_struct *rose_route,
 	for (i = 0; i < rose_node->count; i++) {
 		if (rose_node->neighbour[i] == rose_neigh) {
 			rose_neigh->count--;
+			rose_neigh_put(rose_neigh);
 
 			if (rose_neigh->count == 0) {
 				rose_remove_neigh(rose_neigh);
@@ -430,6 +433,7 @@ int rose_add_loopback_node(const rose_address *address)
 	rose_node_list  = rose_node;
 
 	rose_loopback_neigh->count++;
+	rose_neigh_hold(rose_loopback_neigh);
 
 out:
 	spin_unlock_bh(&rose_node_list_lock);
@@ -461,6 +465,7 @@ void rose_del_loopback_node(const rose_address *address)
 	rose_remove_node(rose_node);
 
 	rose_loopback_neigh->count--;
+	rose_neigh_put(rose_loopback_neigh);
 
 out:
 	spin_unlock_bh(&rose_node_list_lock);
@@ -500,6 +505,7 @@ void rose_rt_device_down(struct net_device *dev)
 				memmove(&t->neighbour[i], &t->neighbour[i + 1],
 					sizeof(t->neighbour[0]) *
 						(t->count - i));
+				rose_neigh_put(s);
 			}
 
 			if (t->count <= 0)
@@ -543,6 +549,7 @@ static int rose_clear_routes(void)
 {
 	struct rose_neigh *s, *rose_neigh;
 	struct rose_node  *t, *rose_node;
+	int i;
 
 	spin_lock_bh(&rose_node_list_lock);
 	spin_lock_bh(&rose_neigh_list_lock);
@@ -553,8 +560,12 @@ static int rose_clear_routes(void)
 	while (rose_node != NULL) {
 		t         = rose_node;
 		rose_node = rose_node->next;
-		if (!t->loopback)
+
+		if (!t->loopback) {
+			for (i = 0; i < rose_node->count; i++)
+				rose_neigh_put(t->neighbour[i]);
 			rose_remove_node(t);
+		}
 	}
 
 	while (rose_neigh != NULL) {
@@ -1186,7 +1197,7 @@ static int rose_neigh_show(struct seq_file *seq, void *v)
 			   (rose_neigh->loopback) ? "RSLOOP-0" : ax2asc(buf, &rose_neigh->callsign),
 			   rose_neigh->dev ? rose_neigh->dev->name : "???",
 			   rose_neigh->count,
-			   refcount_read(&rose_neigh->use) - 1,
+			   refcount_read(&rose_neigh->use) - rose_neigh->count - 1,
 			   (rose_neigh->dce_mode) ? "DCE" : "DTE",
 			   (rose_neigh->restarted) ? "yes" : "no",
 			   ax25_display_timer(&rose_neigh->t0timer) / HZ,
@@ -1291,6 +1302,7 @@ void __exit rose_rt_free(void)
 	struct rose_neigh *s, *rose_neigh = rose_neigh_list;
 	struct rose_node  *t, *rose_node  = rose_node_list;
 	struct rose_route *u, *rose_route = rose_route_list;
+	int i;
 
 	while (rose_neigh != NULL) {
 		s          = rose_neigh;
@@ -1304,6 +1316,8 @@ void __exit rose_rt_free(void)
 		t         = rose_node;
 		rose_node = rose_node->next;
 
+		for (i = 0; i < t->count; i++)
+			rose_neigh_put(t->neighbour[i]);
 		rose_remove_node(t);
 	}
 
-- 
2.39.5 (Apple Git-154)