Re: [PATCH] x86: check boundary in count/setup_resource called by get_current_resources

From: Gary Hade
Date: Thu Nov 01 2007 - 15:13:24 EST

On Thu, Nov 01, 2007 at 01:32:39AM -0700, Andrew Morton wrote:
> On Thu, 01 Nov 2007 01:20:29 -0700 Yinghai Lu <Yinghai.Lu@xxxxxxx> wrote:
> > [PATCH] x86: check boundary in count/setup_resource called by get_current_resources
> >
> > need to check info->res_num less than PCI_BUS_NUM_RESOURCES, so
> > info->bus->resource[info->res_num] = res will not beyond of bus resource array
> > when acpi resutrn too many resource entries.
> >
> Isn't this a bit of a problem? It sounds like PCI_BUS_NUM_RESOURCES is to
> small for that system? If so, some sort of dynamic allocation might be
> needed.

I should have considered the possible resource array overrun
when I created these functions. I had assumed (apparently
incorrectly) that the old PCI_BUS_NUM_RESOURCES value of 4
was based on a spec defined limit on the maximum number of
resources that _CRS can return.

I recently noticed the potential overrun myself while backporting
the code to kernel source where PCI_BUS_NUM_RESOURCES was initially
defined as 4. This happened on a system where the _CRS associated
with one of the root bridges returned 5 resources with the 5th causing
a write beyond the end of the array. Increasing PCI_BUS_NUM_RESOURCES
to the current value of 8 eliminated the overrun that I experienced
but after discovering that there is apparently no limit on the
number of resources that _CRS can return I had intended to post
a change similar to what Yinghai Lu is proposing.

With the current PCI_BUS_NUM_RESOURCES value, _CRS can return
up to 8 resources before the pci_bus resource array is totally
saturated but it should be noted that if a transparent bridge
is present below the root bridge it's child bus will only see
the first 5 resources.

The current fixed pci_bus resource array size of 8 is adequate
(for storing _CRS returned resource and visibility across
transparent bridges) on those systems that I work on but without
a bound on the number of resources returned by _CRS some sort
of dynamic allocation certainly makes sense.

Note that exposure to this issue is currently limited to those
that use the 'pci=use_crs' kernel option.


Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503 IBM T/L: 775-4503

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