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Date:   Tue, 10 Apr 2018 13:42:39 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Ram Pai <linuxram@us.ibm.com>, Bjorn Helgaas <bhelgaas@google.com>,
        Michael Henders <hendersm@shaw.ca>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] resource: Fix integer overflow at reallocation
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        <s5hpo37d5l8.wl-tiwai@suse.de>
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On Tue, 10 Apr 2018 06:54:11 +0200 Takashi Iwai <tiwai@suse.de> wrote:

> On Tue, 10 Apr 2018 02:23:26 +0200,
> Andrew Morton wrote:
> > 
> > On Sun,  8 Apr 2018 09:20:26 +0200 Takashi Iwai <tiwai@suse.de> wrote:
> > 
> > > We've got a bug report indicating a kernel panic at booting on an
> > > x86-32 system, and it turned out to be the invalid resource assigned
> > > after PCI resource reallocation.  __find_resource() first aligns the
> > > resource start address and resets the end address with start+size-1
> > > accordingly, then checks whether it's contained.  Here the end address
> > > may overflow the integer, although resource_contains() still returns
> > > true because the function validates only start and end address.  So
> > > this ends up with returning an invalid resource (start > end).
> > > 
> > > There was already an attempt to cover such a problem in the commit
> > > 47ea91b4052d ("Resource: fix wrong resource window calculation"), but
> > > this case is an overseen one.
> > > 
> > > This patch adds the validity check in resource_contains() to see
> > > whether the given resource has a valid range for avoiding the integer
> > > overflow problem.
> > > 
> > > ...
> > >
> > > --- a/include/linux/ioport.h
> > > +++ b/include/linux/ioport.h
> > > @@ -212,6 +212,9 @@ static inline bool resource_contains(struct resource *r1, struct resource *r2)
> > >  		return false;
> > >  	if (r1->flags & IORESOURCE_UNSET || r2->flags & IORESOURCE_UNSET)
> > >  		return false;
> > > +	/* sanity check whether it's a valid resource range */
> > > +	if (r2->end < r2->start)
> > > +		return false;
> > >  	return r1->start <= r2->start && r1->end >= r2->end;
> > >  }
> > 
> > This doesn't look like the correct place to handle this?  Clearly .end
> > < .start is an invalid state for a resource and we should never have
> > constructed such a thing in the first place?  So adding a check at the
> > place where this resource was initially created seems to be the correct
> > fix?
> 
> Yes, that was also my first thought and actually the v1 patch was like
> that.

Yes, I do prefer.

>  The v2 one was by Ram's suggestion so that we can cover
> potential bugs by all other callers as well.

That could be done as a separate thing?