block/bio: Do not zero user pages

We don't need to zero fill the bio if not using kernel allocated pages.

Fixes: f3587d76 ("block: Clear kernel memory before copying to user") # v4.20-rc2
Reported-by: Todd Aiken <taiken@mvtech.ca>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: stable@vger.kernel.org
Cc: Bart Van Assche <bvanassche@acm.org>
Tested-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1261,7 +1261,8 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
 		if (ret)
 			goto cleanup;
 	} else {
-		zero_fill_bio(bio);
+		if (bmd->is_our_pages)
+			zero_fill_bio(bio);
 		iov_iter_advance(iter, bio->bi_iter.bi_size);
 	}