[PATCH net v3 0/2] ax25: Fix issues of ax25_dev and net_device

[PATCH net v3 0/2] ax25: Fix issues of ax25_dev and net_device

[Duoming Zhou]

The first patch fixes reference count leak issues the object of
"ax25_dev" and "net_device". The second 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 (2):
  ax25: Fix reference count leak issues of ax25_dev and net_device
  ax25: Change kfree() in ax25_dev_free() to ax25_dev_put()

 include/net/ax25.h  |  4 ++--
 net/ax25/ax25_dev.c | 49 ++++++++++++++++-----------------------------
 2 files changed, 19 insertions(+), 34 deletions(-)

-- 
2.17.1

[PATCH net v3 1/2] ax25: Fix reference count leak issues of ax25_dev and net_device

[Duoming Zhou]

The ax25_addr_ax25dev() exists a reference count leak issue of the
object "ax25_dev" and the ax25_dev_device_down() exists reference
count leak issues of the objects "ax25_dev" and "net_device".

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.

There is also a reference count leak issue 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 issues, use kernel circular doubly linked
list to implementate ax25_dev_list. As for ax25_addr_ax25dev() issue,
it is impossible for one pointer to be on a list twice. So add a break
in ax25_addr_ax25dev(). As for ax25_dev_device_down() issues, increase
the reference count of ax25_dev once in ax25_dev_device_up() and decrease
the reference count of ax25_dev and net_device after ax25_dev 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 v3:
  - Use kernel list to implementate ax25_dev_list.
  - Solve reference count leak issues in ax25_dev_device_down().

 include/net/ax25.h  |  4 ++--
 net/ax25/ax25_dev.c | 36 ++++++++++++------------------------
 2 files changed, 14 insertions(+), 26 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..fbaaba0351e 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)
@@ -34,11 +34,13 @@ 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);
+			break;
 		}
+	}
 	spin_unlock_bh(&ax25_dev_lock);
 
 	return res;
@@ -52,6 +54,7 @@ void ax25_dev_device_up(struct net_device *dev)
 {
 	ax25_dev *ax25_dev;
 
+	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;
@@ -85,10 +87,9 @@ 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);
+	dev->ax25_ptr     = ax25_dev;
 
 	ax25_register_dev_sysctl(ax25_dev);
 }
@@ -111,32 +112,19 @@ 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;
-			goto unlock_put;
+	list_for_each_entry(s, &ax25_dev_list, list) {
+		if (s == ax25_dev) {
+			list_del(&s->list);
+			break;
 		}
-
-		s = s->next;
 	}
-	spin_unlock_bh(&ax25_dev_lock);
 	dev->ax25_ptr = NULL;
-	ax25_dev_put(ax25_dev);
-	return;
-
-unlock_put:
 	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);
 }
-- 
2.17.1

[PATCH net v3 2/2] 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>
---
Changes in v3:
  - Make commit messages more clearer.

 net/ax25/ax25_dev.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index fbaaba0351e..8ee028e752f 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -188,16 +188,13 @@ 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;
-		kfree(s);
+	list_for_each_entry_safe(s, n, &ax25_dev_list, list) {
+		netdev_put(s->dev, &s->dev_tracker);
+		list_del(&s->list);
+		ax25_dev_put(s);
 	}
-	ax25_dev_list = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
 }
-- 
2.17.1

Re: [PATCH net v3 1/2] ax25: Fix reference count leak issues of ax25_dev and net_device

[Dan Carpenter]

On Mon, May 06, 2024 at 10:08:34PM +0800, Duoming Zhou wrote:
> The ax25_addr_ax25dev() exists a reference count leak issue of the
> object "ax25_dev" and the ax25_dev_device_down() exists reference
> count leak issues of the objects "ax25_dev" and "net_device".
> 
> 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.
> 
> There is also a reference count leak issue 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 issues, use kernel circular doubly linked
> list to implementate ax25_dev_list. As for ax25_addr_ax25dev() issue,
> it is impossible for one pointer to be on a list twice. So add a break
> in ax25_addr_ax25dev(). As for ax25_dev_device_down() issues, increase
> the reference count of ax25_dev once in ax25_dev_device_up() and decrease
> the reference count of ax25_dev and net_device after ax25_dev 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 v3:
>   - Use kernel list to implementate ax25_dev_list.
>   - Solve reference count leak issues in ax25_dev_device_down().
> 
>  include/net/ax25.h  |  4 ++--
>  net/ax25/ax25_dev.c | 36 ++++++++++++------------------------
>  2 files changed, 14 insertions(+), 26 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..fbaaba0351e 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)
> @@ -34,11 +34,13 @@ 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);
> +			break;
>  		}
> +	}
>  	spin_unlock_bh(&ax25_dev_lock);
>  
>  	return res;
> @@ -52,6 +54,7 @@ void ax25_dev_device_up(struct net_device *dev)
>  {
>  	ax25_dev *ax25_dev;
>  
> +	INIT_LIST_HEAD(&ax25_dev_list);

You can't do this, it will empty the list for each new thing added.
What I wrote is the way to do it.

	/* Initialized the list for the first entry */
	if (!ax25_dev_list.next)
		INIT_LIST_HEAD(&ax25_dev_list);

Just delete the FIXME.  I had thought there is maybe a more beautiful
way to do it but actually it's fine.

>  	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;
> @@ -85,10 +87,9 @@ 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);
> +	dev->ax25_ptr     = ax25_dev;

Please do this while holding the spinlock, otherwise we're not
guaranteed to find find a match in ax25_dev_device_down().  It could
race.

regards,
dan carpenter

Re: [PATCH net v3 1/2] ax25: Fix reference count leak issues of ax25_dev and net_device

[Markus Elfring]

> The ax25_addr_ax25dev() exists a reference count leak issue of the
> object "ax25_dev" and the ax25_dev_device_down() exists reference
> count leak issues of the objects "ax25_dev" and "net_device".

I find that such a wording for the introduction of adjustments needs
further improvements.

How do you think about to offer changes for the affected two function
implementations as separate update steps?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.9-rc7#n81

Regards,
Markus

Re: [PATCH net v3 2/2] ax25: Change kfree() in ax25_dev_free() to ax25_dev_put()

[Markus Elfring]

…
> Replace it with a ax25_dev_put() call instead.
…
> ---
> Changes in v3:
>   - Make commit messages more clearer.
…
> +++ b/net/ax25/ax25_dev.c
> @@ -188,16 +188,13 @@ struct net_device *ax25_fwd_dev(struct net_device *dev)
>   */
>  void __exit ax25_dev_free(void)
>  {
…
> -	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;
> -		kfree(s);
> +	list_for_each_entry_safe(s, n, &ax25_dev_list, list) {
> +		netdev_put(s->dev, &s->dev_tracker);
> +		list_del(&s->list);
> +		ax25_dev_put(s);
>  	}
> -	ax25_dev_list = NULL;
…

Can the increased application of the Linux list API be offered as
a separate update step?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.9-rc7#n81

Regards,
Markus