[PATCH] md: add max_disks bound check in older version

[Aaditya Kansal <aadityakansal390@gmail.com>]

#syz test

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 680b34a63cb3..f5fce41637f1 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1693,6 +1693,12 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
 			desc_nr = rdev2->raid_disk;
 		else
 			desc_nr = next_spare++;
+
+		if (desc_nr >= MD_SB_DISKS) {
+			pr_warn("md: raid_disks = %d exceeds max_disks = %d for version 0.90\n",
+					desc_nr, MD_SB_DISKS);
+			continue;
+		}
 		rdev2->desc_nr = desc_nr;
 		d = &sb->disks[rdev2->desc_nr];
 		nr_disks++;
@@ -1722,7 +1728,7 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
 			d->state |= (1<<MD_DISK_FAILFAST);
 	}
 	/* now set the "removed" and "faulty" bits on any missing devices */
-	for (i=0 ; i < mddev->raid_disks ; i++) {
+	for (i = 0; i < mddev->raid_disks && i < MD_SB_DISKS; i++) {
 		mdp_disk_t *d = &sb->disks[i];
 		if (d->state == 0 && d->number == 0) {
 			d->number = i;
--
2.55.0