linux-kernel - Re: [PATCH v2] resource: Fix integer overflow at reallocation

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Date:   Wed, 11 Apr 2018 07:08:48 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Michael Henders <hendersm@...w.ca>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] resource: Fix integer overflow at reallocation

On Wed, Apr 11, 2018 at 08:16:33AM +0200, Takashi Iwai wrote:
> On Wed, 11 Apr 2018 02:37:44 +0200,
> Ram Pai wrote:
> > 
> > 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@...e.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@...e.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.
> 
> For that purpose, maybe we should do in two folds: at first fix this
> specific issue in __find_resource(), then put the sanity check in
> resource_contains() in addition but with WARN_ON() so that we can
> catch more obviously.

Yes WARN_ON() is a better solution.

do the v1 way for this bug and replace the check in
resource_contains() to a WARN_ON() in a separate patch?

RP