[PATCH 1/6] md/raid5: size the worker group array by nr_node_ids

[Hiroshi Nishida <nishidafmly@gmail.com>]

alloc_thread_groups() sizes conf->worker_groups[] by num_possible_nodes()
-- the number of possible NUMA nodes -- but raid5_wakeup_stripe_thread()
indexes it by cpu_to_group(cpu), i.e. cpu_to_node(cpu), which is a node
id.  When the node map is sparse (for example possible nodes 0 and 2) the
node count is 2 while the largest node id is 2, so the index reaches
worker_groups[2] on a two-element array -- an out-of-bounds access.

This has stayed latent because worker groups are only allocated when
group_thread_cnt is non-zero, and the historical default is 0.  Size the
array by nr_node_ids -- one past the largest possible node id -- so that
indexing by cpu_to_node() is always in bounds.  On a dense node map
nr_node_ids equals num_possible_nodes() and nothing changes; on a sparse
map the array just gains the unused id slots it needs.

Fixes: 851c30c9badf ("raid5: offload stripe handle to workqueue")
Signed-off-by: Hiroshi Nishida <nishidafmly@gmail.com>
---
 drivers/md/raid5.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 0c5c9fb0606e..d8807114a693 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7322,7 +7322,13 @@ static int alloc_thread_groups(struct r5conf *conf, int cnt, int *group_cnt,
 		*worker_groups = NULL;
 		return 0;
 	}
-	*group_cnt = num_possible_nodes();
+	/*
+	 * worker_groups is indexed by cpu_to_group() == cpu_to_node(), a node
+	 * id, so it must have room for the largest possible id.  Size it by
+	 * nr_node_ids (one past that id), not num_possible_nodes(), which is
+	 * only the node count and is smaller on a sparse node map.
+	 */
+	*group_cnt = nr_node_ids;
 	size = sizeof(struct r5worker) * cnt;
 	workers = kcalloc(size, *group_cnt, GFP_NOIO);
 	*worker_groups = kzalloc_objs(struct r5worker_group, *group_cnt,
-- 
2.43.0