linux-kernel - Re: [PATCH] usb: gadget: amd5536udc: fix NULL pointer dereference

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Date:	Fri, 11 Sep 2015 15:32:56 +0530
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
Cc:	Thomas Dahlmann <dahlmann.thomas@...or.de>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-geode@...ts.infradead.org,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: amd5536udc: fix NULL pointer dereference

On Thu, Sep 10, 2015 at 11:03:34AM -0700, David Cohen wrote:
> Hi Sudip,
> 
> On Fri, Sep 04, 2015 at 05:12:23PM +0530, Sudip Mukherjee wrote:
> > We were checking if dev->regs is NULL but it was done after
> > dereferencing it. Lets reset the controller and iounmap dev->regs only
> > if it is not NULL.
> > free_irq() does not need dev->regs, so unmaping it before freeing the
> > irq should not matter.
> > 
> > Signed-off-by: Sudip Mukherjee <sudip@...torindia.org>
> > ---
> >  drivers/usb/gadget/udc/amd5536udc.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/usb/gadget/udc/amd5536udc.c b/drivers/usb/gadget/udc/amd5536udc.c
> > index fdacddb..26066d3 100644
> > --- a/drivers/usb/gadget/udc/amd5536udc.c
> > +++ b/drivers/usb/gadget/udc/amd5536udc.c
> > @@ -3135,11 +3135,12 @@ static void udc_pci_remove(struct pci_dev *pdev)
<snip>
> 
> I'm not familiar with the driver, but you're iounmap'ing before freeing
> irq. Looks fishy to me.
Well, I thought you will be able to give me some idea about how fix it. :)
Then I guess we should be on the safe side and what about the following:


diff --git a/drivers/usb/gadget/udc/amd5536udc.c b/drivers/usb/gadget/udc/amd5536udc.c
index fdacddb..82f36f6 100644
--- a/drivers/usb/gadget/udc/amd5536udc.c
+++ b/drivers/usb/gadget/udc/amd5536udc.c
@@ -3134,8 +3134,9 @@ static void udc_pci_remove(struct pci_dev *pdev)
 		pci_pool_destroy(dev->stp_requests);
 	}
 
-	/* reset controller */
-	writel(AMD_BIT(UDC_DEVCFG_SOFTRESET), &dev->regs->cfg);
+	if (dev->regs)
+		/* reset controller */
+		writel(AMD_BIT(UDC_DEVCFG_SOFTRESET), &dev->regs->cfg);
 	if (dev->irq_registered)
 		free_irq(pdev->irq, dev);
 	if (dev->regs)

And just for my information: for a device what might happen if I iounmap
before I free the irq? One thing I can think of is that after iounmap
just at that moment one interrupt comes and the driver tries to access
the io memory while servicing the irq.

regards
sudip
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