[PATCH v7 07/11] iomap: fix iomap_dio_zero() for fs bs > system page size

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

From: Pankaj Raghav <p.raghav@samsung.com>

iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
< fs block size. iomap_dio_zero() has an implicit assumption that fs block
size < page_size. This is true for most filesystems at the moment.

If the block size > page size, this will send the contents of the page
next to zero page(as len > PAGE_SIZE) to the underlying block device,
causing FS corruption.

iomap is a generic infrastructure and it should not make any assumptions
about the fs block size and the page size of the system.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
---
 fs/internal.h          |  5 +++++
 fs/iomap/buffered-io.c |  6 ++++++
 fs/iomap/direct-io.c   | 26 ++++++++++++++++++++++++--
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 84f371193f74..30217f0ff4c6 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -35,6 +35,11 @@ static inline void bdev_cache_init(void)
 int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 		get_block_t *get_block, const struct iomap *iomap);
 
+/*
+ * iomap/direct-io.c
+ */
+int iomap_dio_init(void);
+
 /*
  * char_dev.c
  */
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 49938419fcc7..9f791db473e4 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1990,6 +1990,12 @@ EXPORT_SYMBOL_GPL(iomap_writepages);
 
 static int __init iomap_init(void)
 {
+	int ret;
+
+	ret = iomap_dio_init();
+	if (ret)
+		return ret;
+
 	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
 			   offsetof(struct iomap_ioend, io_bio),
 			   BIOSET_NEED_BVECS);
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index f3b43d223a46..b95600b254a3 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -27,6 +27,13 @@
 #define IOMAP_DIO_WRITE		(1U << 30)
 #define IOMAP_DIO_DIRTY		(1U << 31)
 
+/*
+ * Used for sub block zeroing in iomap_dio_zero()
+ */
+#define ZERO_FSB_SIZE (65536)
+#define ZERO_FSB_ORDER (get_order(ZERO_FSB_SIZE))
+static struct page *zero_fs_block;
+
 struct iomap_dio {
 	struct kiocb		*iocb;
 	const struct iomap_dio_ops *dops;
@@ -52,6 +59,16 @@ struct iomap_dio {
 	};
 };
 
+int iomap_dio_init(void)
+{
+	zero_fs_block = alloc_pages(GFP_KERNEL | __GFP_ZERO, ZERO_FSB_ORDER);
+
+	if (!zero_fs_block)
+		return -ENOMEM;
+
+	return 0;
+}
+
 static struct bio *iomap_dio_alloc_bio(const struct iomap_iter *iter,
 		struct iomap_dio *dio, unsigned short nr_vecs, blk_opf_t opf)
 {
@@ -236,17 +253,22 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		loff_t pos, unsigned len)
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
-	struct page *page = ZERO_PAGE(0);
 	struct bio *bio;
 
+	/*
+	 * Max block size supported is 64k
+	 */
+	WARN_ON_ONCE(len > ZERO_FSB_SIZE);
+
 	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 				  GFP_KERNEL);
+
 	bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	__bio_add_page(bio, page, len, 0);
+	__bio_add_page(bio, zero_fs_block, len, 0);
 	iomap_dio_submit_bio(iter, dio, bio, pos);
 }
 
-- 
2.44.1