cpumask: zero extra bits in alloc_cpumask_var_node

Impact: extra safety checks during transition When CONFIG_CPUMASKS_OFFSTACK is set, the new cpumask_ operators only use bits up to nr_cpu_ids, not NR_CPUS. Using the old cpus_ operators on these masks can mean accessing undefined bits. After some discussion, Mike and I decided to err on the side of caution; we zero the "undefined" bits in alloc_cpumask_var_node() until all the old cpumask functions are removed. Signed-off-by: Rusty Russell <[email protected]>
ambv · Dec 31, 2008 · 2a53008 · 2a53008
1 parent 5db0e1e
commit 2a53008
Showing 1 changed file with 8 additions and 0 deletions.
diff --git a/lib/cpumask.c b/lib/cpumask.c
@@ -107,6 +107,14 @@ bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node)
 		dump_stack();
 	}
 #endif
+	/* FIXME: Bandaid to save us from old primitives which go to NR_CPUS. */
+	if (*mask) {
+		unsigned int tail;
+		tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
+		memset(cpumask_bits(*mask) + cpumask_size() - tail,
+		       0, tail);
+	}
+
 	return *mask != NULL;
 }
 EXPORT_SYMBOL(alloc_cpumask_var_node);