software node: Prevent link creation failure from causing kobj reference count imbalance

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>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250414071123.1228331-1-lizhi.xu@windriver.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index b1726a3515f6fbe13c2186af1f74479263798e42..5c78fa6ae77257a9c40049a42631d27367092fca 100644 (file)
--- 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)