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

[Takashi Iwai <tiwai@suse.de>]

On Mon, 02 Apr 2018 22:35:04 +0200,
Takashi Iwai wrote:
> 
> 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.

FWIW, below is the revised one to move the check into
resource_contains().

My concern is, however, that the resource validity check isn't a job
of resource_contains().  OTOH, this may avoid other similar cases, so
it might be worth.

In anyway, if there is no objection, and anyone else doesn't want to
take, I'll forward this to Andrew as a poor orphan kid.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH v2] resource: Fix integer overflow at reallocation

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 in resource_contains() to see
whether the given resource has a valid range for avoiding the integer
overflow problem.

Bugzilla: http://bugzilla.opensuse.org/show_bug.cgi?id=1086739
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>
---
 include/linux/ioport.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index da0ebaec25f0..466d7be046eb 100644
--- 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;
 }
 
-- 
2.16.3