From db3e24a02e29b507c24c0adb4d22914c65dab763 Mon Sep 17 00:00:00 2001 From: Ryusuke Konishi <konishi.ryusuke@gmail.com> Date: Sat, 11 May 2024 09:29:42 +0900 Subject: [PATCH] nilfs2: make block erasure safe in nilfs_finish_roll_forward() The implementation of writing a zero-fill block in nilfs_finish_roll_forward() is not safe. The buffer is being cleared without acquiring a lock or setting the uptodate flag, so theoretically, between the time the buffer's data is cleared and the time it is written back to the block device using sync_dirty_buffer(), that zero data can be undone by concurrent block device reads. Since this buffer points to a location that has been read from disk once, the uptodate flag will most likely remain, but since it was obtained with __getblk(), that is not guaranteed. In other words, this is exceptional, and this function itself is not normally called (only once when mounting after a specific pattern of unclean shutdown), so it is highly unlikely that this will actually cause a problem. Anyway, eliminate this potential race issue by protecting the clearing of buffer data with a buffer lock and setting the buffer's uptodate flag within the protected section. Link: https://lkml.kernel.org/r/20240511002942.9608-1-konishi.ryusuke@gmail.com Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- fs/nilfs2/recovery.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/nilfs2/recovery.c b/fs/nilfs2/recovery.c index 020f304c600e..b638dc06df2f 100644 --- a/fs/nilfs2/recovery.c +++ b/fs/nilfs2/recovery.c @@ -702,8 +702,12 @@ static void nilfs_finish_roll_forward(struct the_nilfs *nilfs, if (WARN_ON(!bh)) return; /* should never happen */ + lock_buffer(bh); memset(bh->b_data, 0, bh->b_size); + set_buffer_uptodate(bh); set_buffer_dirty(bh); + unlock_buffer(bh); + err = sync_dirty_buffer(bh); if (unlikely(err)) nilfs_warn(nilfs->ns_sb, -- 2.49.0