[RFC PATCH] can: raw: add missing refcount for memory leak fix

[Oliver Hartkopp <socketcan@xxxxxxxxxxxx>]

Commit ee8b94c8510c ("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: ee8b94c8510c ("can: raw: fix receiver memory leak")
Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
---
 net/can/raw.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index e10f59375659..a61c417fdd27 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -283,12 +283,14 @@ static void raw_notify(struct raw_sock *ro, unsigned long msg,
 
 	switch (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);
+			dev_put(dev);
+		}
 
 		if (ro->count > 1)
 			kfree(ro->filter);
 
 		ro->ifindex = 0;
@@ -389,14 +391,16 @@ static int raw_release(struct socket *sock)
 	rtnl_lock();
 	lock_sock(sk);
 
 	/* remove current filters & unregister */
 	if (ro->bound) {
-		if (ro->dev)
+		if (ro->dev) {
 			raw_disable_allfilters(dev_net(ro->dev), ro->dev, sk);
-		else
+			dev_put(ro->dev);
+		} else {
 			raw_disable_allfilters(sock_net(sk), NULL, sk);
+		}
 	}
 
 	if (ro->count > 1)
 		kfree(ro->filter);
 
@@ -447,36 +451,43 @@ static int raw_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 		if (dev->type != ARPHRD_CAN) {
 			dev_put(dev);
 			err = -ENODEV;
 			goto out;
 		}
-		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) {
+			dev_put(dev);
+			goto out;
+		}
+
+		ifindex = dev->ifindex;
+		if (!(dev->flags & IFF_UP))
+			notify_enetdown = 1;
 	} else {
 		ifindex = 0;
 
 		/* filters set by default/setsockopt */
 		err = raw_enable_allfilters(sock_net(sk), NULL, sk);
 	}
 
 	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 */
+				dev_put(ro->dev);
+			} else {
 				raw_disable_allfilters(sock_net(sk), NULL, sk);
+			}
 		}
 		ro->ifindex = ifindex;
 		ro->bound = 1;
+		/* bind() ok -> holding a reference to new ro->dev */
 		ro->dev = dev;
 	}
 
  out:
 	release_sock(sk);
-- 
2.39.2