md: avoid array overflow with bad v1.x metadata

We trust the 'desc_nr' field in v1.x metadata enough to use it
as an index in an array.  This isn't really safe.
So range-check the value first.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c194955..249b289 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1308,7 +1308,12 @@ static int super_1_validate(mddev_t *mddev, mdk_rdev_t *rdev)
        }
        if (mddev->level != LEVEL_MULTIPATH) {
                int role;
-               role = le16_to_cpu(sb->dev_roles[rdev->desc_nr]);
+               if (rdev->desc_nr < 0 ||
+                   rdev->desc_nr >= le32_to_cpu(sb->max_dev)) {
+                       role = 0xffff;
+                       rdev->desc_nr = -1;
+               } else
+                       role = le16_to_cpu(sb->dev_roles[rdev->desc_nr]);
                switch(role) {
                case 0xffff: /* spare */
                        break;