+ nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward.patch added to mm-nonmm-unstable branch

+ nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: nilfs2: make block erasure safe in nilfs_finish_roll_forward()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Subject: nilfs2: make block erasure safe in nilfs_finish_roll_forward()
Date: Sat, 11 May 2024 09:29:42 +0900

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(+)

--- a/fs/nilfs2/recovery.c~nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward
+++ a/fs/nilfs2/recovery.c
@@ -702,8 +702,12 @@ static void nilfs_finish_roll_forward(st
 	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,
_

Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-make-block-erasure-safe-in-nilfs_finish_roll_forward.patch