[PATCH v2 5/6] iomap: don't mark blocks uptodate after partial zeroing

Zhang Yi
2024-08-12T12:16:25Z

From: Zhang Yi <yi.zhang@huawei.com>

In __iomap_write_begin(), if we unaligned buffered write data to a hole
of a regular file, we only zero out the place where aligned to block
size that we don't want to write, but mark the whole range uptodate if
block size < folio size. This is wrong since the not zeroed part will
contains stale data and can be accessed by a concurrent buffered read
easily (on the filesystem may not hold inode->i_rwsem) once we mark the
range uptodate. Fix this by drop iomap_set_range_uptodate() in the
zeroing out branch.

Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads")
Reported-by: Matthew Wilcox <willy@infradead.org>
Closes: https://lore.kernel.org/all/ZqsN5ouQTEc1KAzV@casper.infradead.org/
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
fs/iomap/buffered-io.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index ac762de9a27f..96600405dbb5 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -744,8 +744,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
poff, plen, srcmap);
if (status)
return status;
+ iomap_set_range_uptodate(folio, poff, plen);
}
- iomap_set_range_uptodate(folio, poff, plen);
} while ((block_start += plen) < block_end);

return 0;
--
2.39.2