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Subject[patch 020/123] x86/PCI: Prevent mmconfig memory corruption
2.6.33-stable review patch.  If anyone has any objections, please let me know.

-----------------

From: Thomas Gleixner <tglx@linutronix.de>

commit bb8d41330ce27edb91adb6922d3f8e1a8923f727 upstream.

commit ff097ddd4 (x86/PCI: MMCONFIG: manage pci_mmcfg_region as a
list, not a table) introduced a nasty memory corruption when
pci_mmcfg_list is empty.

pci_mmcfg_check_end_bus_number() dereferences pci_mmcfg_list.prev even
when the list is empty. The following write hits some variable near to
pci_mmcfg_list.

Further down a similar problem exists, where cfg->list.next is
dereferenced unconditionally and a comparison with some variable near
to pci_mmcfg_list happens.

Add a check for the last element into the for_each_entry() loop and
remove all the other crappy logic which is just a leftover of the old
array based code which was replaced by the list conversion.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/pci/mmconfig-shared.c | 17 ++++++-----------
1 file changed, 6 insertions(+), 11 deletions(-)

--- a/arch/x86/pci/mmconfig-shared.c
+++ b/arch/x86/pci/mmconfig-shared.c
@@ -303,22 +303,17 @@ static void __init pci_mmcfg_check_end_b
{
struct pci_mmcfg_region *cfg, *cfgx;

- /* last one*/
- cfg = list_entry(pci_mmcfg_list.prev, typeof(*cfg), list);
- if (cfg)
- if (cfg->end_bus < cfg->start_bus)
- cfg->end_bus = 255;
-
- if (list_is_singular(&pci_mmcfg_list))
- return;
-
- /* don't overlap please */
+ /* Fixup overlaps */
list_for_each_entry(cfg, &pci_mmcfg_list, list) {
if (cfg->end_bus < cfg->start_bus)
cfg->end_bus = 255;

+ /* Don't access the list head ! */
+ if (cfg->list.next == &pci_mmcfg_list)
+ break;
+
cfgx = list_entry(cfg->list.next, typeof(*cfg), list);
- if (cfg != cfgx && cfg->end_bus >= cfgx->start_bus)
+ if (cfg->end_bus >= cfgx->start_bus)
cfg->end_bus = cfgx->start_bus - 1;
}
}



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