x86/numa: Add constraints check for nid parameters

This patch adds constraint checks to the numa_set_distance()
function.

When the check triggers (this should not happen normally) it
emits a warning and avoids a store to a negative index in
numa_distance[] array - i.e. avoids memory corruption.

Negative ids can be passed when the pxm-to-nids mapping is not
properly filled while parsing the SRAT.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Anton Arapov <anton@redhat.com>
Link: http://lkml.kernel.org/r/20111208121640.GA2229@dhcp-27-244.brq.redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/numa.c

@@ -430,17 +430,19 @@ static int __init numa_alloc_distance(void)
  * calls are ignored until the distance table is reset with
  * numa_reset_distance().
  *
- * If @from or @to is higher than the highest known node at the time of
- * table creation or @distance doesn't make sense, the call is ignored.
+ * If @from or @to is higher than the highest known node or lower than zero
+ * at the time of table creation or @distance doesn't make sense, the call
+ * is ignored.
  * This is to allow simplification of specific NUMA config implementations.
  */
 void __init numa_set_distance(int from, int to, int distance)
 {
 	if (!numa_distance && numa_alloc_distance() < 0)
 		return;
 
-	if (from >= numa_distance_cnt || to >= numa_distance_cnt) {
-		printk_once(KERN_DEBUG "NUMA: Debug: distance out of bound, from=%d to=%d distance=%d\n",
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
+		pr_warn_once("NUMA: Warning: node ids are out of bound, from=%d to=%d distance=%d\n",
 			    from, to, distance);
 		return;
 	}