[PATCH] block: fix bio_copy_user_iov() for SG_DXFER_TO_FROM_DEV case

[Mingming Gu]

Commit "block: Fix WARNING in _copy_from_iter" is insufficient to make
SG_IO ioctl with a transfer direction of SG_DXFER_TO_FROM_DEV work;
the passed in iterator should be advanced after bio_copy_from_iter().
Otherwise its caller, blk_rq_map_user_iov(), will return -EINVAL due
to a wrong loop condition.

Instead of using a copy of the passed iterator, save iter->data_source
and restore it after bio_copy_from_iter().

Signed-off-by: Mingming Gu <mmgu@xxxxxxxxxxxxxxxxxx>
---
 block/blk-map.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index 71210cd..eca02d9 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -211,11 +211,12 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data,
 		if (ret)
 			goto cleanup;
 	} else if (map_data && map_data->from_user) {
-		struct iov_iter iter2 = *iter;
+		bool tmp = iter->data_source;
 
 		/* This is the copy-in part of SG_DXFER_TO_FROM_DEV. */
-		iter2.data_source = ITER_SOURCE;
-		ret = bio_copy_from_iter(bio, &iter2);
+		iter->data_source = ITER_SOURCE;
+		ret = bio_copy_from_iter(bio, iter);
+		iter->data_source = tmp;
 		if (ret)
 			goto cleanup;
 	} else {
-- 
2.7.4