Re: [PATCH] resource: Fix integer overflow at reallocation

[Takashi Iwai <tiwai@suse.de>]

On Mon, 02 Apr 2018 21:09:03 +0200,
Ram Pai wrote:
> 
> On Mon, Apr 02, 2018 at 09:16:16AM +0200, Takashi Iwai 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 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 of the newly calculated resource
> > for avoiding the integer overflow problem.
> 
> Should we move this check "alloc.start <= alloc.end" into resource_contains()?
> Doing so will catch all uses of such erroneous (overflowing) resources.

I thought of it, too.  OTOH, it's rather a validity check and doesn't
belong to resource_contains() semantics.  If the function returns
false, you don't know whether it's an invalid resource or it's really
not contained.

We may return an error code, but I'm not sure whether such an API
change is needed.  Maybe not.


thanks,

Takashi


> 
> RP
> 
> > 
> > Bugzilla: https://urldefense.proofpoint.com/v2/url?u=http-3A__bugzilla.opensuse.org_show-5Fbug.cgi-3Fid-3D1086739&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=m-UrKChQVkZtnPpjbF6YY99NbT8FBByQ-E-ygV8luxw&m=FoiwlR-LTJ9_EBQsLYSCqXuWrGhU1lXycdvhbaK7wOk&s=clxOtFUIAMlPNwQJZTaKnmIta9pMtJ8XprmwVd-ylvo&e=
> > Fixes: 23c570a67448 ("resource: ability to resize an allocated resource")
> > Reported-and-tested-by: Michael Henders <hendersm@shaw.ca>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > ---
> > 
> > Bjorn, I send this to you since the bug hits during PCI init, although
> > the culprit is in generic resource management.
> > 
> >  kernel/resource.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index e270b5048988..2af6c03858b9 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -651,7 +651,8 @@ static int __find_resource(struct resource *root, struct resource *old,
> >  			alloc.start = constraint->alignf(constraint->alignf_data, &avail,
> >  					size, constraint->align);
> >  			alloc.end = alloc.start + size - 1;
> > -			if (resource_contains(&avail, &alloc)) {
> > +			if (alloc.start <= alloc.end &&
> > +			    resource_contains(&avail, &alloc)) {
> >  				new->start = alloc.start;
> >  				new->end = alloc.end;
> >  				return 0;
> > -- 
> > 2.16.2
> 
> -- 
> Ram Pai
>