dm era: Verify the data block size hasn't changed

dm-era doesn't support changing the data block size of existing devices,
so check explicitly that the requested block size for a new target
matches the one stored in the metadata.

Fixes: eec40579 ("dm: add era target")
Cc: stable@vger.kernel.org # v3.15+
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-era-target.c

@@ -564,6 +564,15 @@ static int open_metadata(struct era_metadata *md)
 	}
 
 	disk = dm_block_data(sblock);
+
+	/* Verify the data block size hasn't changed */
+	if (le32_to_cpu(disk->data_block_size) != md->block_size) {
+		DMERR("changing the data block size (from %u to %llu) is not supported",
+		      le32_to_cpu(disk->data_block_size), md->block_size);
+		r = -EINVAL;
+		goto bad;
+	}
+
 	r = dm_tm_open_with_sm(md->bm, SUPERBLOCK_LOCATION,
 			       disk->metadata_space_map_root,
 			       sizeof(disk->metadata_space_map_root),
@@ -575,7 +584,6 @@ static int open_metadata(struct era_metadata *md)
 
 	setup_infos(md);
 
-	md->block_size = le32_to_cpu(disk->data_block_size);
 	md->nr_blocks = le32_to_cpu(disk->nr_blocks);
 	md->current_era = le32_to_cpu(disk->current_era);