drbd: fix potential data corruption and protocol error

We assumed only bios with bi_idx == 0 would end up
in drbd_make_request().

That is wrong.

At least device mapper, in __clone_and_map(), may submit
clones only covering a partial bio, but sharing
the original bvec, by adjusting bi_idx and relevant
other bio members of the clone.

We used __bio_for_each_segment() in various places,
even though that is documented as
 * drivers should not use the __ version unless they _really_ want to
 * run through the entire bio and not just pending pieces

Impact: we would send the full bio bvec, even for the clone
with bi_idx > 0, which will cause data corruption on the
peer (because we submit wrong data at the clone offset),
and will cause a DRBD protocol error, disconnect/reconnect
and resync (thus fixing the corruption),
because the next package header would be expected right
in the middle of the sent data, causing DRBD magic mismatch.

Fix: drop the assert, and use bio_for_each_segment()
instead of the __ version.

Conflicts:

	drbd/drbd_tracing.c

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 0 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 4fc7f98d9856..de319ba54241 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1106,7 +1106,6 @@ void drbd_make_request(struct request_queue *q, struct bio *bio)
          */
         D_ASSERT(bio->bi_size > 0);
         D_ASSERT((bio->bi_size & 0x1ff) == 0);
-        D_ASSERT(bio->bi_idx == 0);
 
         /* to make some things easier, force alignment of requests within the
          * granularity of our hash tables */