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Date: Thu, 2 May 2024 10:56:43 +0300
From: Dan Carpenter <dan.carpenter@linaro.org>
To: duoming@zju.edu.cn
Cc: linux-hams@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, pabeni@redhat.com, kuba@kernel.org,
	edumazet@google.com, davem@davemloft.net, jreuter@yaina.de,
	lars@oddbit.com, Miroslav Skoric <skoric@uns.ac.rs>
Subject: Re: [PATCH net] ax25: Fix refcount leak issues of ax25_dev
Message-ID: <8767454a-2d5a-4c6d-b887-440047c9bc5b@moroto.mountain>
References: <20240501060218.32898-1-duoming@zju.edu.cn>
 <7fcfdc9a-e3f3-49a1-9373-39b5ad745799@moroto.mountain>
 <1402dfc8.20a4b.18f37963e87.Coremail.duoming@zju.edu.cn>
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In-Reply-To: <1402dfc8.20a4b.18f37963e87.Coremail.duoming@zju.edu.cn>

On Thu, May 02, 2024 at 12:35:44PM +0800, duoming@zju.edu.cn wrote:
> On Wed, 1 May 2024 20:43:37 +0300 Dan Carpenter wrote:
> > I'm always happy to take credit for stuff but the Reported by should go
> > to Lars and Miroslav.
> > 
> > Reported-by: Lars Kellogg-Stedman <lars@oddbit.com>
> > Reported-by: Miroslav Skoric <skoric@uns.ac.rs>
> 
> This patch is not related with the problem raised by Lars Kellogg-Stedman
> and Miroslav Skoric, it only solves the reference counting leak issues of
> ax25_dev in ax25_addr_ax25dev() and ax25_dev_device_down(). So I think
> there is no need to change the "Reported by" label.
> 

Ah...  I was really hoping it was related to the other bugs.

Okay, what about we separate this into different patches one for each
bug?  The changes to ax25_addr_ax25dev() and ax25_dev_free() are
obvious and could go in as-is but as two separate patches.

The changes to ax25_dev_device_up/down() are more subtle.

The ax25_dev_list stuff is frustrating.  It would be so much easier if
it were a normal list and you could just do:

        /*
         *      Remove any packet forwarding that points to this device.
         */
        list_for_each_entry(s, ax25_dev_list, list) {
                if (s->forward == dev)
                        s->forward = NULL;
        }

        list_for_each_entry(s, ax25_dev_list, list) {
                if (s == ax25_dev) {
                        list_del(s);
                        free_net = true;
                        break;
                }
        }

        spin_unlock_bh(&ax25_dev_lock);
        dev->ax25_ptr = NULL;
        if (free_net)
                netdev_put(dev, &ax25_dev->dev_tracker);
        ax25_dev_put(ax25_dev);
}

Why do we call netdev_put() on that one path?  Btw, here is an untested
conversion to lists...

regards,
dan carpenter

diff --git a/include/net/ax25.h b/include/net/ax25.h
index 0d939e5aee4e..c2a85fd3f5ea 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -216,7 +216,7 @@ typedef struct {
 struct ctl_table;
 
 typedef struct ax25_dev {
-	struct ax25_dev		*next;
+	struct list_head	list;
 
 	struct net_device	*dev;
 	netdevice_tracker	dev_tracker;
@@ -330,7 +330,6 @@ int ax25_addr_size(const ax25_digi *);
 void ax25_digi_invert(const ax25_digi *, ax25_digi *);
 
 /* ax25_dev.c */
-extern ax25_dev *ax25_dev_list;
 extern spinlock_t ax25_dev_lock;
 
 #if IS_ENABLED(CONFIG_AX25)
diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index 282ec581c072..b632af38f1e1 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -22,11 +22,12 @@
 #include <net/sock.h>
 #include <linux/uaccess.h>
 #include <linux/fcntl.h>
+#include <linux/list.h>
 #include <linux/mm.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
 
-ax25_dev *ax25_dev_list;
+static struct list_head ax25_dev_list;
 DEFINE_SPINLOCK(ax25_dev_lock);
 
 ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
@@ -34,11 +35,12 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
 	ax25_dev *ax25_dev, *res = NULL;
 
 	spin_lock_bh(&ax25_dev_lock);
-	for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
+	list_for_each_entry(ax25_dev, &ax25_dev_list, list) {
 		if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
 			res = ax25_dev;
 			ax25_dev_hold(ax25_dev);
 		}
+	}
 	spin_unlock_bh(&ax25_dev_lock);
 
 	return res;
@@ -52,6 +54,10 @@ void ax25_dev_device_up(struct net_device *dev)
 {
 	ax25_dev *ax25_dev;
 
+	// FIXME: do call this in probe or something
+	if (!ax25_dev_list.next)
+		INIT_LIST_HEAD(&ax25_dev_list);
+
 	ax25_dev = kzalloc(sizeof(*ax25_dev), GFP_KERNEL);
 	if (!ax25_dev) {
 		printk(KERN_ERR "AX.25: ax25_dev_device_up - out of memory\n");
@@ -85,8 +91,7 @@ void ax25_dev_device_up(struct net_device *dev)
 #endif
 
 	spin_lock_bh(&ax25_dev_lock);
-	ax25_dev->next = ax25_dev_list;
-	ax25_dev_list  = ax25_dev;
+	list_add(&ax25_dev->list, &ax25_dev_list);
 	spin_unlock_bh(&ax25_dev_lock);
 	ax25_dev_hold(ax25_dev);
 
@@ -111,23 +116,18 @@ void ax25_dev_device_down(struct net_device *dev)
 	/*
 	 *	Remove any packet forwarding that points to this device.
 	 */
-	for (s = ax25_dev_list; s != NULL; s = s->next)
+	list_for_each_entry(s, &ax25_dev_list, list) {
 		if (s->forward == dev)
 			s->forward = NULL;
-
-	if ((s = ax25_dev_list) == ax25_dev) {
-		ax25_dev_list = s->next;
-		goto unlock_put;
 	}
 
-	while (s != NULL && s->next != NULL) {
-		if (s->next == ax25_dev) {
-			s->next = ax25_dev->next;
+	list_for_each_entry(s, &ax25_dev_list, list) {
+		if (s == ax25_dev) {
+			list_del(&s->list);
 			goto unlock_put;
 		}
-
-		s = s->next;
 	}
+
 	spin_unlock_bh(&ax25_dev_lock);
 	dev->ax25_ptr = NULL;
 	ax25_dev_put(ax25_dev);
@@ -200,16 +200,13 @@ struct net_device *ax25_fwd_dev(struct net_device *dev)
  */
 void __exit ax25_dev_free(void)
 {
-	ax25_dev *s, *ax25_dev;
+	ax25_dev *s, *n;
 
 	spin_lock_bh(&ax25_dev_lock);
-	ax25_dev = ax25_dev_list;
-	while (ax25_dev != NULL) {
-		s        = ax25_dev;
-		netdev_put(ax25_dev->dev, &ax25_dev->dev_tracker);
-		ax25_dev = ax25_dev->next;
+	list_for_each_entry_safe(s, n, &ax25_dev_list, list) {
+		netdev_put(s->dev, &s->dev_tracker);
+		list_del(&s->list);
 		kfree(s);
 	}
-	ax25_dev_list = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
 }