linux-kernel - Re: [PATCH] intel-iommu: Fix array overflow

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Date:	Thu, 25 Oct 2007 09:31:02 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	mgross@...ux.intel.com
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	anil.s.keshavamurthy@...el.com
Subject: Re: [PATCH] intel-iommu: Fix array overflow

At Wed, 24 Oct 2007 16:30:37 -0700,
Mark Gross wrote:
> 
> On Tue, Oct 23, 2007 at 10:57:51AM +0200, Takashi Iwai wrote:
> > Fix possible array overflow:
> > 
> > drivers/pci/intel-iommu.c: In function ‘dmar_get_fault_reason’:
> > drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds
> > drivers/pci/intel-iommu.c: In function ‘iommu_page_fault’:
> > drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds
> > 
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > 
> > ---
> >  drivers/pci/intel-iommu.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> > index b3d7031..e4b0a0d 100644
> > --- a/drivers/pci/intel-iommu.c
> > +++ b/drivers/pci/intel-iommu.c
> > @@ -749,8 +749,8 @@ static char *fault_reason_strings[] =
> >  
> >  char *dmar_get_fault_reason(u8 fault_reason)
> >  {
> > -	if (fault_reason > MAX_FAULT_REASON_IDX)
> > -		return fault_reason_strings[MAX_FAULT_REASON_IDX];
> > +	if (fault_reason >= MAX_FAULT_REASON_IDX)
> > +		return fault_reason_strings[MAX_FAULT_REASON_IDX - 1];
> 
> This looks like what the code meant to implement.

I think not.  The size of fault_reason_strings[] is
MAX_FAULT_REASON_IDX, not + 1.  So gcc warning is correct.
Maybe the main problem is that the constant name is confusing...


Takashi

>  I guess future
> hardware may be able to generate more types of faults, otherwise I'd put
> a BUG here.
> 
> --mgross
> 
> 
> >  	else
> >  		return fault_reason_strings[fault_reason];
> >  }
> > -
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