[RFC v2 10/14] iomap: fix iomap_dio_zero() for fs bs > system page size

Pankaj Raghav (Samsung)
2024-02-13T09:37:59Z

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>
---
fs/iomap/direct-io.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index bcd3f8cf5ea4..04f6c5548136 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -239,14 +239,23 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
struct page *page = ZERO_PAGE(0);
struct bio *bio;

- bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
+ WARN_ON_ONCE(len > (BIO_MAX_VECS * PAGE_SIZE));
+
+ bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS,
+ 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);
+ while (len) {
+ unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);
+
+ __bio_add_page(bio, page, io_len, 0);
+ len -= io_len;
+ }
iomap_dio_submit_bio(iter, dio, bio, pos);
}

--
2.43.0