can: raw: add missing refcount for memory leak fix

Commit ee8b94c ("can: raw: fix receiver memory leak") introduced
a new reference to the CAN netdevice that has assigned CAN filters.
But this new ro->dev reference did not maintain its own refcount which
lead to another KASAN use-after-free splat found by Eric Dumazet.

This patch ensures a proper refcount for the CAN nedevice.

Fixes: ee8b94c ("can: raw: fix receiver memory leak")
Reported-by: Eric Dumazet <edumazet@google.com>
Cc: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20230821144547.6658-3-socketcan@hartkopp.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: hartkopp

net/can/raw.c

@@ -85,6 +85,7 @@ struct raw_sock {
 	int bound;
 	int ifindex;
 	struct net_device *dev;
+	netdevice_tracker dev_tracker;
 	struct list_head notifier;
 	int loopback;
 	int recv_own_msgs;
@@ -285,8 +286,10 @@ static void raw_notify(struct raw_sock *ro, unsigned long msg,
 	case NETDEV_UNREGISTER:
 		lock_sock(sk);
 		/* remove current filters & unregister */
-		if (ro->bound)
+		if (ro->bound) {
 			raw_disable_allfilters(dev_net(dev), dev, sk);
+			netdev_put(dev, &ro->dev_tracker);
+		}
 
 		if (ro->count > 1)
 			kfree(ro->filter);
@@ -391,10 +394,12 @@ static int raw_release(struct socket *sock)
 
 	/* remove current filters & unregister */
 	if (ro->bound) {
-		if (ro->dev)
+		if (ro->dev) {
 			raw_disable_allfilters(dev_net(ro->dev), ro->dev, sk);
-		else
+			netdev_put(ro->dev, &ro->dev_tracker);
+		} else {
 			raw_disable_allfilters(sock_net(sk), NULL, sk);
+		}
 	}
 
 	if (ro->count > 1)
@@ -445,18 +450,20 @@ static int raw_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 			goto out;
 		}
 		if (dev->type != ARPHRD_CAN) {
-			dev_put(dev);
 			err = -ENODEV;
-			goto out;
+			goto out_put_dev;
 		}
+
 		if (!(dev->flags & IFF_UP))
 			notify_enetdown = 1;
 
 		ifindex = dev->ifindex;
 
 		/* filters set by default/setsockopt */
 		err = raw_enable_allfilters(sock_net(sk), dev, sk);
-		dev_put(dev);
+		if (err)
+			goto out_put_dev;
+
 	} else {
 		ifindex = 0;
 
@@ -467,18 +474,28 @@ static int raw_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 	if (!err) {
 		if (ro->bound) {
 			/* unregister old filters */
-			if (ro->dev)
+			if (ro->dev) {
 				raw_disable_allfilters(dev_net(ro->dev),
 						       ro->dev, sk);
-			else
+				/* drop reference to old ro->dev */
+				netdev_put(ro->dev, &ro->dev_tracker);
+			} else {
 				raw_disable_allfilters(sock_net(sk), NULL, sk);
+			}
 		}
 		ro->ifindex = ifindex;
 		ro->bound = 1;
+		/* bind() ok -> hold a reference for new ro->dev */
 		ro->dev = dev;
+		if (ro->dev)
+			netdev_hold(ro->dev, &ro->dev_tracker, GFP_KERNEL);
 	}
 
- out:
+out_put_dev:
+	/* remove potential reference from dev_get_by_index() */
+	if (dev)
+		dev_put(dev);
+out:
 	release_sock(sk);
 	rtnl_unlock();