linux-kernel - [PATCH RESEND net v4 3/4] ax25: Fix reference count leak issues of net

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Date: Tue,  7 May 2024 14:21:54 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	linux-hams@...r.kernel.org,
	pabeni@...hat.com,
	kuba@...nel.org,
	edumazet@...gle.com,
	davem@...emloft.net,
	jreuter@...na.de,
	horms@...nel.org,
	Markus.Elfring@....de,
	dan.carpenter@...aro.org,
	lars@...bit.com,
	Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH RESEND net v4 3/4] ax25: Fix reference count leak issues of net_device

The ax25_dev_device_down() exists reference count leak issues of
the object "net_device". When the ax25 device is shutting down.
The ax25_dev_device_down() drops the reference count of net_device
one or zero times depending on if we goto unlock_put or not, which
will cause memory leak.

In order to solve the above issue, decrease the reference count of
net_device after dev->ax25_ptr is set to null.

Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <dan.carpenter@...aro.org>
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
Changes in v4:
  - Make the fix procedure of net_device as a separate update steps.

 net/ax25/ax25_dev.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index 6a572fe1046..05e556cdc2b 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -120,15 +120,9 @@ void ax25_dev_device_down(struct net_device *dev)
 	list_for_each_entry(s, &ax25_dev_list, list) {
 		if (s == ax25_dev) {
 			list_del(&s->list);
-			goto unlock_put;
+			break;
 		}
 	}
-	dev->ax25_ptr = NULL;
-	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_put(ax25_dev);
-	return;
-
-unlock_put:
 	dev->ax25_ptr = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
 	netdev_put(dev, &ax25_dev->dev_tracker);
-- 
2.17.1