linux-kernel - Re: [PATCH] USB: EHCI: tegra: Fix use-after-free in .remove()

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Date:	Tue, 17 Jun 2014 15:30:34 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Stephen Warren <swarren@...dotorg.org>
cc:	Tuomas Tynkkynen <ttynkkynen@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: EHCI: tegra: Fix use-after-free in .remove()

On Tue, 17 Jun 2014, Stephen Warren wrote:

> On 06/17/2014 08:17 AM, Tuomas Tynkkynen wrote:
> > The tegra_ehci_hcd structure is located in the private space allocated
> > by the core USB code so it must not be accessed after the HCD is
> > freed.
> 
> > diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> 
> This seems to be a persistent problem. Witness commit ecc8a0cdca18 "usb:
> host: tegra: fix warning messages in ehci_remove". So, I wonder if ...
> 
> > @@ -479,10 +479,11 @@ static int tegra_ehci_remove(struct platform_device *pdev)
> >  
> >  	usb_phy_shutdown(hcd->phy);
> >  	usb_remove_hcd(hcd);
> > -	usb_put_hcd(hcd);
> >  
> >  	clk_disable_unprepare(tegra->clk);
> >  
> 
> It's worth putting a comment here:
> 
> 	/* This must be last, since *tegra is part of *hcd */
> > +	usb_put_hcd(hcd);
> > +
> >  	return 0;
> >  }

Well, maybe.  At this stage it's not too likely that anything will be 
added after the usb_put_hcd().

> Of course, that could be a separate commit if you want.

This affects more than ehci-tegra.  The same concept applies to all the 
EHCI and OHCI platform drivers that use the platform-private area.

Alan Stern

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