[PATCH net v4 0/4] ax25: Fix issues of ax25_dev and net_device

[PATCH net v4 0/4] ax25: Fix issues of ax25_dev and net_device

[Duoming Zhou]

The first patch use kernel universal linked list to implement
ax25_dev_list, which makes the operation of the list easier.
The second and third patch fix reference count leak issues of
the object "ax25_dev" and "net_device". The last patch uses
ax25_dev_put() to replace kfree() in ax25_dev_free().

You can see the former discussion in the following link:
https://lore.kernel.org/netdev/20240501060218.32898-1-duoming@zju.edu.cn/

Duoming Zhou (4):
  ax25: Use kernel universal linked list to implement ax25_dev_list
  ax25: Fix reference count leak issues of ax25_dev
  ax25: Fix reference count leak issues of net_device
  ax25: Change kfree() in ax25_dev_free() to ax25_dev_put()

 include/net/ax25.h  |  4 ++--
 net/ax25/ax25_dev.c | 51 ++++++++++++++++-----------------------------
 2 files changed, 20 insertions(+), 35 deletions(-)

-- 
2.17.1

[PATCH net v4 1/4] ax25: Use kernel universal linked list to implement ax25_dev_list

[Duoming Zhou]

The origin ax25_dev_list implements its own single linked list,
which is complicated and error-prone. For example, when deleting
the node of ax25_dev_list in ax25_dev_device_down(), we have to
operate on the head node and other nodes separately.

This patch uses kernel universal linked list to replace original
ax25_dev_list, which make the operation of ax25_dev_list easier.
There are two points that need to notice:

[1] We should add a check to judge whether the list is empty before
INIT_LIST_HEAD in ax25_dev_device_up(), otherwise it will empty the
list for each new ax25_dev added.

[2] We should do "dev->ax25_ptr = ax25_dev;" and "dev->ax25_ptr = NULL;"
while holding the spinlock, otherwise the ax25_dev_device_up() and
ax25_dev_device_down() could race, we're not guaranteed to find a match
ax25_dev in ax25_dev_device_down().

Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in v4:
  - Make the linux list API as a separate update step.
  - Add a check before INIT_LIST_HEAD.
  - Do "dev->ax25_ptr = ax25_dev;" while holding the spinlock.

 include/net/ax25.h  |  4 ++--
 net/ax25/ax25_dev.c | 42 +++++++++++++++++-------------------------
 2 files changed, 19 insertions(+), 27 deletions(-)

diff --git a/include/net/ax25.h b/include/net/ax25.h
index 0d939e5aee4..92c6aa4f9a6 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 +330,7 @@ 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;
+static struct list_head 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 282ec581c07..d4e1e36a6a8 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -22,11 +22,11 @@
 #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;
 DEFINE_SPINLOCK(ax25_dev_lock);
 
 ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
@@ -34,7 +34,7 @@ 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);
@@ -52,6 +52,9 @@ void ax25_dev_device_up(struct net_device *dev)
 {
 	ax25_dev *ax25_dev;
 
+	/* Initialized the list for the first entry */
+	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");
@@ -59,7 +62,6 @@ void ax25_dev_device_up(struct net_device *dev)
 	}
 
 	refcount_set(&ax25_dev->refcount, 1);
-	dev->ax25_ptr     = ax25_dev;
 	ax25_dev->dev     = dev;
 	netdev_hold(dev, &ax25_dev->dev_tracker, GFP_KERNEL);
 	ax25_dev->forward = NULL;
@@ -85,8 +87,8 @@ 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);
+	dev->ax25_ptr     = ax25_dev;
 	spin_unlock_bh(&ax25_dev_lock);
 	ax25_dev_hold(ax25_dev);
 
@@ -111,32 +113,25 @@ 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;
+	spin_unlock_bh(&ax25_dev_lock);
 	ax25_dev_put(ax25_dev);
 	return;
 
 unlock_put:
+	dev->ax25_ptr = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
 	ax25_dev_put(ax25_dev);
-	dev->ax25_ptr = NULL;
 	netdev_put(dev, &ax25_dev->dev_tracker);
 	ax25_dev_put(ax25_dev);
 }
@@ -200,16 +195,13 @@ 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);
 }
-- 
2.17.1

[PATCH net v4 2/4] ax25: Fix reference count leak issues of ax25_dev

[Duoming Zhou]

The ax25_addr_ax25dev() and ax25_dev_device_down() exist a reference
count leak issue of the object "ax25_dev".

Memory leak issue in ax25_addr_ax25dev():

The reference count of the object "ax25_dev" can be increased multiple
times in ax25_addr_ax25dev(). This will cause a memory leak so far.

Memory leak issues in ax25_dev_device_down():

The reference count of ax25_dev is set to 1 in ax25_dev_device_up() and
then increase the reference count when ax25_dev is added to ax25_dev_list.
As a result, the reference count of ax25_dev is 2. But when the device is
shutting down. The ax25_dev_device_down() drops the reference count once
or twice depending on if we goto unlock_put or not, which will cause
memory leak.

As for the issue of ax25_addr_ax25dev(), it is impossible for one pointer
to be on a list twice. So add a break in ax25_addr_ax25dev(). As for the
issue of ax25_dev_device_down(), increase the reference count of ax25_dev
once in ax25_dev_device_up() and decrease the reference count of ax25_dev
after it is removed from the ax25_dev_list.

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

 net/ax25/ax25_dev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index d4e1e36a6a8..6a572fe1046 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -38,6 +38,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
 		if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
 			res = ax25_dev;
 			ax25_dev_hold(ax25_dev);
+			break;
 		}
 	spin_unlock_bh(&ax25_dev_lock);
 
@@ -90,7 +91,6 @@ void ax25_dev_device_up(struct net_device *dev)
 	list_add(&ax25_dev->list, &ax25_dev_list);
 	dev->ax25_ptr     = ax25_dev;
 	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_hold(ax25_dev);
 
 	ax25_register_dev_sysctl(ax25_dev);
 }
@@ -131,7 +131,6 @@ void ax25_dev_device_down(struct net_device *dev)
 unlock_put:
 	dev->ax25_ptr = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_put(ax25_dev);
 	netdev_put(dev, &ax25_dev->dev_tracker);
 	ax25_dev_put(ax25_dev);
 }
-- 
2.17.1

[PATCH net v4 3/4] ax25: Fix reference count leak issues of net_device

[Duoming Zhou]

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@linaro.org>
Signed-off-by: Duoming Zhou <duoming@zju.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

[PATCH net v4 4/4] ax25: Change kfree() in ax25_dev_free() to ax25_dev_put()

[Duoming Zhou]

The object "ax25_dev" is managed by reference counting. Thus it should
not be directly released by a kfree() call in ax25_dev_free(). Replace
it with a ax25_dev_put() call instead.

Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
 net/ax25/ax25_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index 05e556cdc2b..d4d29879df2 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -194,7 +194,7 @@ void __exit ax25_dev_free(void)
 	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_put(s)
 	}
 	spin_unlock_bh(&ax25_dev_lock);
 }
-- 
2.17.1