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 <rusty@rustcorp.com.au>

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/cpumask.c b/lib/cpumask.c
index 8e1496cb63f7..3389e2440da0 100644
--- 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);