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nilfs2: make block erasure safe in nilfs_finish_roll_forward()

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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>
This commit is contained in:
Ryusuke Konishi 2024-05-11 09:29:42 +09:00 committed by Andrew Morton
parent 28d2188709
commit db3e24a02e
1 changed files with 4 additions and 0 deletions
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4
fs/nilfs2/recovery.c
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@ -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,