x86/PCI: Prevent mmconfig memory corruption

KAGA-KOKO · jbarnes993 · commit bb8d41330ce2 · 2010-02-25T08:30:58.000-08:00
commit ff097dd (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> Cc: stable@kernel.org Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git 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_bus_number(void)
 {
 	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;
 	}
 }
