[PATCH 3.12 094/170] rbd: handle parent_overlap on writes correctly

Jiri Slaby
2014-07-18T13:11:52Z

From: Ilya Dryomov <ilya.dryomov@inktank.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 9638556a276125553549fdfe349c464481ec2f39 upstream.

The following check in rbd_img_obj_request_submit()

rbd_dev->parent_overlap <= obj_request->img_offset

allows the fall through to the non-layered write case even if both
parent_overlap and obj_request->img_offset belong to the same RADOS
object. This leads to data corruption, because the area to the left of
parent_overlap ends up unconditionally zero-filled instead of being
populated with parent data. Suppose we want to write 1M to offset 6M
of image bar, which is a clone of foo@snap; object_size is 4M,
parent_overlap is 5M:

rbd_data.<id>.0000000000000001
---------------------|----------------------|------------
| should be copyup'ed | should be zeroed out | write ...
---------------------|----------------------|------------
4M 5M 6M
parent_overlap obj_request->img_offset

4..5M should be copyup'ed from foo, yet it is zero-filled, just like
5..6M is.

Given that the only striping mode kernel client currently supports is
chunking (i.e. stripe_unit == object_size, stripe_count == 1), round
parent_overlap up to the next object boundary for the purposes of the
overlap check.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/block/rbd.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index af7b44ffd190..aeeb62e0981a 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1379,6 +1379,14 @@ static bool obj_request_exists_test(struct rbd_obj_request *obj_request)
return test_bit(OBJ_REQ_EXISTS, &obj_request->flags) != 0;
}

+static bool obj_request_overlaps_parent(struct rbd_obj_request *obj_request)
+{
+ struct rbd_device *rbd_dev = obj_request->img_request->rbd_dev;
+
+ return obj_request->img_offset <
+ round_up(rbd_dev->parent_overlap, rbd_obj_bytes(&rbd_dev->header));
+}
+
static void rbd_obj_request_get(struct rbd_obj_request *obj_request)
{
dout("%s: obj %p (was %d)\n", __func__, obj_request,
@@ -2675,7 +2683,7 @@ static int rbd_img_obj_request_submit(struct rbd_obj_request *obj_request)
*/
if (!img_request_write_test(img_request) ||
!img_request_layered_test(img_request) ||
- rbd_dev->parent_overlap <= obj_request->img_offset ||
+ !obj_request_overlaps_parent(obj_request) ||
((known = obj_request_known_test(obj_request)) &&
obj_request_exists_test(obj_request))) {

--
2.0.0