From: Kiyoshi Ueda <[email-masked]>

This patch prevents access to mapped_device which is being deleted.

Currently, even after a mapped_device has been removed from the hash,
it could be accessed through idr_find() using minor number.
That could cause a race and NULL pointer reference below:
  CPU0                          CPU1
  ------------------------------------------------------------------
  dev_remove(param)
    down_write(_hash_lock)
    dm_lock_for_deletion(md)
      spin_lock(_minor_lock)
      set_bit(DMF_DELETING)
      spin_unlock(_minor_lock)
    __hash_remove(hc)
    up_write(_hash_lock)
                                dev_status(param)
                                  md = find_device(param)
                                         down_read(_hash_lock)
                                         __find_device_hash_cell(param)
                                           dm_get_md(param->dev)
                                             md = dm_find_md(dev)
                                                    spin_lock(_minor_lock)
                                                    md = idr_find(MINOR(dev))
                                                    spin_unlock(_minor_lock)
    dm_put(md)
      free_dev(md)
                                             dm_get(md)
                                         up_read(_hash_lock)
                                  __dev_status(md, param)
                                  dm_put(md)

This patch fixes such problems.

Signed-off-by: Kiyoshi Ueda <[email-masked]>
Signed-off-by: Jun'ichi Nomura <[email-masked]>
Cc: [email-masked]
Signed-off-by: Alasdair G Kergon <[email-masked]>

---
 drivers/md/dm.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6.35/drivers/md/dm.c
===================================================================
--- linux-2.6.35.orig/drivers/md/dm.c
+++ linux-2.6.35/drivers/md/dm.c
@@ -2136,6 +2136,7 @@ static struct mapped_device *dm_find_md(
 	md = idr_find(&_minor_idr, minor);
 	if (md && (md == MINOR_ALLOCED ||
 		   (MINOR(disk_devt(dm_disk(md))) != minor) ||
+		   dm_deleting_md(md) ||
 		   test_bit(DMF_FREEING, &md->flags))) {
 		md = NULL;
 		goto out;