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[PATCH V2] software node: Prevent link creation failure from causing kobj reference count imbalance

Lizhi Xu posted 1 patch 8 months, 1 week ago 
drivers/base/swnode.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
[PATCH V2] software node: Prevent link creation failure from causing kobj reference count imbalance
Posted by Lizhi Xu 8 months, 1 week ago 
syzbot reported a uaf in software_node_notify_remove. [1]

When any of the two sysfs_create_link() in software_node_notify() fails,
the swnode->kobj reference count will not increase normally, which will
cause swnode to be released incorrectly due to the imbalance of kobj reference
count when executing software_node_notify_remove().

Increase the reference count of kobj before creating the link to avoid uaf.

[1]
BUG: KASAN: slab-use-after-free in software_node_notify_remove+0x1bc/0x1c0 drivers/base/swnode.c:1108
Read of size 1 at addr ffff888033c08908 by task syz-executor105/5844
Freed by task 5844:
 software_node_notify_remove+0x159/0x1c0 drivers/base/swnode.c:1106
 device_platform_notify_remove drivers/base/core.c:2387 [inline]

Fixes: 9eb59204d519 ("iommufd/selftest: Add set_dev_pasid in mock iommu")
Reported-by: syzbot+2ff22910687ee0dfd48e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2ff22910687ee0dfd48e
Tested-by: syzbot+2ff22910687ee0dfd48e@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
---
V1 -> V2: reduce calltrace

 drivers/base/swnode.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index b1726a3515f6..5c78fa6ae772 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -1080,6 +1080,7 @@ void software_node_notify(struct device *dev)
 	if (!swnode)
 		return;
 
+	kobject_get(&swnode->kobj);
 	ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
 	if (ret)
 		return;
@@ -1089,8 +1090,6 @@ void software_node_notify(struct device *dev)
 		sysfs_remove_link(&dev->kobj, "software_node");
 		return;
 	}
-
-	kobject_get(&swnode->kobj);
 }
 
 void software_node_notify_remove(struct device *dev)
-- 
2.43.0
Re: [PATCH V2] software node: Prevent link creation failure from causing kobj reference count imbalance
Posted by Sakari Ailus 8 months, 1 week ago 
On Mon, Apr 14, 2025 at 03:11:23PM +0800, Lizhi Xu wrote:
> syzbot reported a uaf in software_node_notify_remove. [1]
> 
> When any of the two sysfs_create_link() in software_node_notify() fails,
> the swnode->kobj reference count will not increase normally, which will
> cause swnode to be released incorrectly due to the imbalance of kobj reference
> count when executing software_node_notify_remove().
> 
> Increase the reference count of kobj before creating the link to avoid uaf.
> 
> [1]
> BUG: KASAN: slab-use-after-free in software_node_notify_remove+0x1bc/0x1c0 drivers/base/swnode.c:1108
> Read of size 1 at addr ffff888033c08908 by task syz-executor105/5844
> Freed by task 5844:
>  software_node_notify_remove+0x159/0x1c0 drivers/base/swnode.c:1106
>  device_platform_notify_remove drivers/base/core.c:2387 [inline]
> 
> Fixes: 9eb59204d519 ("iommufd/selftest: Add set_dev_pasid in mock iommu")
> Reported-by: syzbot+2ff22910687ee0dfd48e@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2ff22910687ee0dfd48e
> Tested-by: syzbot+2ff22910687ee0dfd48e@syzkaller.appspotmail.com
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>

Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>

> ---
> V1 -> V2: reduce calltrace
> 
>  drivers/base/swnode.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index b1726a3515f6..5c78fa6ae772 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -1080,6 +1080,7 @@ void software_node_notify(struct device *dev)
>  	if (!swnode)
>  		return;
>  
> +	kobject_get(&swnode->kobj);
>  	ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
>  	if (ret)
>  		return;
> @@ -1089,8 +1090,6 @@ void software_node_notify(struct device *dev)
>  		sysfs_remove_link(&dev->kobj, "software_node");
>  		return;
>  	}
> -
> -	kobject_get(&swnode->kobj);
>  }
>  
>  void software_node_notify_remove(struct device *dev)
> -- 
> 2.43.0
> 

-- 
Sakari Ailus
Re: [PATCH V2] software node: Prevent link creation failure from causing kobj reference count imbalance
Posted by Andy Shevchenko 8 months, 1 week ago 
On Mon, Apr 14, 2025 at 03:11:23PM +0800, Lizhi Xu wrote:
> syzbot reported a uaf in software_node_notify_remove. [1]
> 
> When any of the two sysfs_create_link() in software_node_notify() fails,
> the swnode->kobj reference count will not increase normally, which will
> cause swnode to be released incorrectly due to the imbalance of kobj reference
> count when executing software_node_notify_remove().
> 
> Increase the reference count of kobj before creating the link to avoid uaf.
> 
> [1]
> BUG: KASAN: slab-use-after-free in software_node_notify_remove+0x1bc/0x1c0 drivers/base/swnode.c:1108
> Read of size 1 at addr ffff888033c08908 by task syz-executor105/5844
> Freed by task 5844:
>  software_node_notify_remove+0x159/0x1c0 drivers/base/swnode.c:1106
>  device_platform_notify_remove drivers/base/core.c:2387 [inline]

The fix looks correct to me,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko

Patchew 2.1-devel-b67e4c2

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