[PATCH v1 2/2] md/raid5: reject invalid reshape disks in raid5_run()

[Chen Cheng]

From: Chen Cheng <chencheng@xxxxxxxxx>

Check disk count before dividing by data disks while assembling a
reshape, otherwise too few disks can cause division by zero.

Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Signed-off-by: Chen Cheng <chencheng@xxxxxxxxx>
---
 drivers/md/raid5.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4ab31af34b9f..bb0dd9324811 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -8051,10 +8051,11 @@ static int raid5_run(struct mddev *mddev)
 		 * the array in read-only mode, so we check for that.
 		 */
 		sector_t here_new, here_old;
 		int old_disks;
 		int max_degraded = (mddev->level == 6 ? 2 : 1);
+		int min_disks = min_raid_disks(mddev->level);
 		int chunk_sectors;
 		int new_data_disks;
 
 		if (journal_dev) {
 			pr_warn("md/raid:%s: don't support reshape with journal - aborting.\n",
@@ -8066,10 +8067,16 @@ static int raid5_run(struct mddev *mddev)
 			pr_warn("md/raid:%s: unsupported reshape required - aborting.\n",
 				mdname(mddev));
 			return -EINVAL;
 		}
 		old_disks = mddev->raid_disks - mddev->delta_disks;
+		if (mddev->raid_disks < min_disks || old_disks < min_disks) {
+			pr_warn("md/raid:%s: invalid reshape disks (%d -> %d, min %d)\n",
+				mdname(mddev), old_disks, mddev->raid_disks,
+				min_disks);
+			return -EINVAL;
+		}
 		/* reshape_position must be on a new-stripe boundary, and one
 		 * further up in new geometry must map after here in old
 		 * geometry.
 		 * If the chunk sizes are different, then as we perform reshape
 		 * in units of the largest of the two, reshape_position needs
-- 
2.55.0