linux-kernel - Bug in sysfs_break_active

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9c2484f4-df62-4d23-97a2-55a160eba55f@rowland.harvard.edu>
Date: Mon, 4 Mar 2024 14:17:27 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Tejun Heo <tj@...nel.org>, Greg KH <gregkh@...uxfoundation.org>
Cc: Kernel development list <linux-kernel@...r.kernel.org>
Subject: Bug in sysfs_break_active_protection()

Tejun:

It looks like there's a memory leak in sysfs_break_active_protection().  
It and its companion routine do this:

struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
						  const struct attribute *attr)
{
	struct kernfs_node *kn;

	kobject_get(kobj);
	kn = kernfs_find_and_get(kobj->sd, attr->name);
	if (kn)
		kernfs_break_active_protection(kn);
	return kn;
}

void sysfs_unbreak_active_protection(struct kernfs_node *kn)
{
	struct kobject *kobj = kn->parent->priv;

	kernfs_unbreak_active_protection(kn);
	kernfs_put(kn);
	kobject_put(kobj);
}

If kn is NULL then the kobject_get(kobj) reference is never dropped.  
It looks like this could happen if two processes want to unregister the 
same kobject at the same time.

Shouldn't sysfs_break_active_protection() do this?

	kobject_get(kobj);
	kn = kernfs_find_and_get(kobj->sd, attr->name);
	if (kn)
		kernfs_break_active_protection(kn);
+	else
+		kobject_put(kobj);
	return kn;

Alan Stern