linux-kernel - Re: [PATCH] usb: gadget: composite: unlock spinlock before usb_gadget

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] [day] [month] [year] [list]

Message-ID: <20140619134805.GC23782@saruman.home>
Date:	Thu, 19 Jun 2014 08:48:05 -0500
From:	Felipe Balbi <balbi@...com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	"'Robert Baldyga'" <r.baldyga@...sung.com>,
	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"andrzej.p@...sung.com" <andrzej.p@...sung.com>
Subject: Re: [PATCH] usb: gadget: composite: unlock spinlock before
 usb_gadget_disconnect()

On Fri, Jun 13, 2014 at 11:36:24AM +0000, David Laight wrote:
> From: Robert Baldyga
> > usb_gadget_disconnect() shouldn't be called under spinlock to avoid
> > spinlock recursion. Function usb_gadget_disconnect() calls pullup(),
> > which is callback from UDC driver, usually calling composite_disconnect().
> > This function wants to lock spinlock used in usb_function_deactivate()
> > causing spinlock recursion.
> ...
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -260,8 +260,11 @@ int usb_function_deactivate(struct usb_function *function)
> > 
> >  	spin_lock_irqsave(&cdev->lock, flags);
> > 
> > -	if (cdev->deactivations == 0)
> > +	if (cdev->deactivations == 0) {
> > +		spin_unlock_irqrestore(&cdev->lock, flags);
> >  		status = usb_gadget_disconnect(cdev->gadget);
> > +		spin_lock_irqsave(&cdev->lock, flags);
> > +	}
> >  	if (status == 0)
> >  		cdev->deactivations++;
> 
> That sort of change rings big alarm bells.
> You've effectively isolated the usb_gadget_disconnect() call
> from the check that cdev->deactivations == 0.
> And then you increment cdev->deactivations below.
> 
> Looks like it will be racy to me.

yes, it will. Fixing this requires a much more involved change.

-- 
balbi

Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)