block: fix leaking page ref on truncated direct io

The size being added to a bio from an iov is aligned to a block size
after the pages were gotten. If the new aligned size truncates the last
page, its reference was being leaked. Ensure all pages that were not
added to the bio have their reference released.

Since this essentially requires doing the same that bio_put_pages(), and
there was only one caller for that function, this patch makes the
put_page() loop common for everyone.

Fixes: b1a000d3b8 ("block: relax direct io memory alignment")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20220712153256.2202024-3-kbusch@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1151,14 +1151,6 @@ void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
 	bio_set_flag(bio, BIO_CLONED);
 }
 
-static void bio_put_pages(struct page **pages, size_t size, size_t off)
-{
-	size_t i, nr = DIV_ROUND_UP(size + (off & ~PAGE_MASK), PAGE_SIZE);
-
-	for (i = 0; i < nr; i++)
-		put_page(pages[i]);
-}
-
 static int bio_iov_add_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int offset)
 {
@@ -1207,7 +1199,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
 	struct page **pages = (struct page **)bv;
 	ssize_t size, left;
-	unsigned len, i;
+	unsigned len, i = 0;
 	size_t offset;
 	int ret = 0;
 
@@ -1228,10 +1220,16 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	 */
 	size = iov_iter_get_pages(iter, pages, UINT_MAX - bio->bi_iter.bi_size,
 				  nr_pages, &offset);
-	if (size > 0)
+	if (size > 0) {
+		nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE);
 		size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));
-	if (unlikely(size <= 0))
-		return size ? size : -EFAULT;
+	} else
+		nr_pages = 0;
+
+	if (unlikely(size <= 0)) {
+		ret = size ? size : -EFAULT;
+		goto out;
+	}
 
 	for (left = size, i = 0; left > 0; left -= len, i++) {
 		struct page *page = pages[i];
@@ -1240,10 +1238,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
 			ret = bio_iov_add_zone_append_page(bio, page, len,
 					offset);
-			if (ret) {
-				bio_put_pages(pages + i, left, offset);
+			if (ret)
 				break;
-			}
 		} else
 			bio_iov_add_page(bio, page, len, offset);
 
@@ -1251,6 +1247,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	}
 
 	iov_iter_advance(iter, size - left);
+out:
+	while (i < nr_pages)
+		put_page(pages[i++]);
+
 	return ret;
 }