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

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Message-ID: <20250414071123.1228331-1-lizhi.xu@windriver.com>
Date: Mon, 14 Apr 2025 15:11:23 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <andriy.shevchenko@...ux.intel.com>
CC: <dakr@...nel.org>, <djrscally@...il.com>, <dvyukov@...gle.com>,
        <gregkh@...uxfoundation.org>, <heikki.krogerus@...ux.intel.com>,
        <jgg@...dia.com>, <kevin.tian@...el.com>, <linux-acpi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lizhi.xu@...driver.com>,
        <nicolinc@...dia.com>, <rafael@...nel.org>,
        <sakari.ailus@...ux.intel.com>,
        <syzbot+2ff22910687ee0dfd48e@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>, <yi.l.liu@...el.com>
Subject: [PATCH V2] 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@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2ff22910687ee0dfd48e
Tested-by: syzbot+2ff22910687ee0dfd48e@...kaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@...driver.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