[PATCH for 2.6.15] Make sure interleave masks have at least one node set

[Andi Kleen <ak@suse.de>]

Otherwise a bad mem policy system call can confuse the interleaving
code into referencing undefined nodes.

Originally reported by Doug Chapman

I was told it's CVE-2005-3358
(one has to love these security people - they make everything sound important) 

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux-2.6.15rc7-work/mm/mempolicy.c
===================================================================
--- linux-2.6.15rc7-work.orig/mm/mempolicy.c
+++ linux-2.6.15rc7-work/mm/mempolicy.c
@@ -161,6 +161,10 @@ static struct mempolicy *mpol_new(int mo
 	switch (mode) {
 	case MPOL_INTERLEAVE:
 		policy->v.nodes = *nodes;
+		if (nodes_weight(*nodes) == 0) {
+			kmem_cache_free(policy_cache, policy);
+			return ERR_PTR(-EINVAL);
+		}
 		break;
 	case MPOL_PREFERRED:
 		policy->v.preferred_node = first_node(*nodes);
-
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