md: Ensure an md array never has too many devices.

Each different metadata format supported by md supports a
different maximum number of devices.
We really should be enforcing this maximum in the kernel, but
we aren't quite doing that properly.

We currently only enforce it at the 'hot_add' point, which is an
older interface which is not used by current userspace.

We need to also enforce it at 'add_new_disk' time for active arrays
and at 'do_md_run' time when starting a new array.

So move the test from 'hot_add' into 'bind_rdev_to_array' which is
called from both 'hot_add' and 'add_new_disk, and add a new
test in 'analyse_sbs' which is called from 'do_md_run'.

This bug (or missing feature) has been around "forever" and so
the patch is suitable for any -stable that is currently maintained.

Cc: stable@kernel.org

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

1 files changed, 14 insertions, 10 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 41e2509bf896..4495104f6c9f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1481,6 +1481,11 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
                 if (find_rdev_nr(mddev, rdev->desc_nr))
                         return -EBUSY;
         }
+        if (mddev->max_disks && rdev->desc_nr >= mddev->max_disks) {
+                printk(KERN_WARNING "md: %s: array is limited to %d devices\n",
+                       mdname(mddev), mddev->max_disks);
+                return -EBUSY;
+        }
         bdevname(rdev->bdev,b);
         while ( (s=strchr(b, '/')) != NULL)
                 *s = '!';
@@ -2441,6 +2446,15 @@ static void analyze_sbs(mddev_t * mddev)
 
         i = 0;
         rdev_for_each(rdev, tmp, mddev) {
+                if (rdev->desc_nr >= mddev->max_disks ||
+                    i > mddev->max_disks) {
+                        printk(KERN_WARNING
+                               "md: %s: %s: only %d devices permitted\n",
+                               mdname(mddev), bdevname(rdev->bdev, b),
+                               mddev->max_disks);
+                        kick_rdev_from_array(rdev);
+                        continue;
+                }
                 if (rdev != freshest)
                         if (super_types[mddev->major_version].
                             validate_super(mddev, rdev)) {
@@ -4614,13 +4628,6 @@ static int hot_add_disk(mddev_t * mddev, dev_t dev)
          * noticed in interrupt contexts ...
          */
 
-        if (rdev->desc_nr == mddev->max_disks) {
-                printk(KERN_WARNING "%s: can not hot-add to full array!\n",
-                        mdname(mddev));
-                err = -EBUSY;
-                goto abort_unbind_export;
-        }
-
         rdev->raid_disk = -1;
 
         md_update_sb(mddev, 1);
@@ -4634,9 +4641,6 @@ static int hot_add_disk(mddev_t * mddev, dev_t dev)
         md_new_event(mddev);
         return 0;
 
-abort_unbind_export:
-        unbind_rdev_from_array(rdev);
-
 abort_export:
         export_rdev(rdev);
         return err;