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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.