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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=2ff22910687ee0dfd48e
> Tested-by: syzbot+2ff22910687ee0dfd48e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
Reviewed-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> ---
> 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
