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Date:   Tue, 10 Apr 2018 17:37:44 -0700
From:   Ram Pai <linuxram@us.ibm.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Takashi Iwai <tiwai@suse.de>, 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
Reply-To: Ram Pai <linuxram@us.ibm.com>
References: <20180408072026.27365-1-tiwai@suse.de>
 <20180409172326.944143fd13db2601e4dee9b0@linux-foundation.org>
 <s5hpo37d5l8.wl-tiwai@suse.de>
 <20180410134239.483fe34525db647f2f3d1ece@linux-foundation.org>
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On Tue, Apr 10, 2018 at 01:42:39PM -0700, Andrew Morton wrote:
> 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?

the first approach will fix overflows in just that particular case. The
second approach will catch and error-out overflows anywhere. There is a
short-term down side to the second approach; it might cause a slew of
error reports but will eventually help clean up all bad behavior.

RP