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>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c194955aecae..249b2896d4ea 100644
--- 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;