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When a buffer is unpinned by xfs_buf_item_unpin(), we need to access the buffer after we've dropped the buffer log item reference count. This opens a window where we can have two racing unpins for the buffer item (e.g. shutdown checkpoint context callback processing racing with journal IO iclog completion processing) and both attempt to access the buffer after dropping the BLI reference count. If we are unlucky, the "BLI freed" context wins the race and frees the buffer before the "BLI still active" case checks the buffer pin count. This results in a use after free that can only be triggered in active filesystem shutdown situations. To fix this, we need to ensure that buffer existence extends beyond the BLI reference count checks and until the unpin processing is complete. This implies that a buffer pin operation must also take a buffer reference to ensure that the buffer cannot be freed until the buffer unpin processing is complete. Reported-by: yangerkun <yangerkun@huawei.com> Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dave Chinner <david@fromorbit.com>
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 Restructured Text 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.