[PATCH v2 2/3] ublk: check for ublk_unmap_io() returning 0

If the userspace ublk server passes an unmapped address as the data
buffer for a completed ublk read, ublk_unmap_io() will return 0
indicating no bytes could be copied. Currently, this will result in
calling blk_update_request() with nr_bytes=0, which doesn't seem
supported. Fail the I/O with BLK_STS_IOERR in this case instead.

Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Caleb Sander Mateos <[email protected]>
---
 drivers/block/ublk_drv.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 098e046505ad..2cbc359dc196 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1588,12 +1588,18 @@ static inline void __ublk_complete_rq(struct request *req, struct ublk_io *io,
 	/*
 	 * Extremely impossible since we got data filled in just before
 	 *
 	 * Re-read simply for this unlikely case.
 	 */
-	if (unlikely(unmapped_bytes < io->res))
+	if (unlikely(unmapped_bytes < io->res)) {
+		if (unlikely(!unmapped_bytes)) {
+			res = BLK_STS_IOERR;
+			goto exit;
+		}
+
 		io->res = unmapped_bytes;
+	}
 
 	/*
 	 * Run bio->bi_end_io() with softirqs disabled. If the final fput
 	 * happens off this path, then that will prevent ublk's blkdev_release()
 	 * from being called on current's task work, see fput() implementation.
-- 
2.54.0