Darrick J. Wong b1f38c3ec6 xfs: don't replace the wrong part of the cow fork
[ Upstream commit a1caeeadbf ]

LOLLM points out that xfs_iext_lookup_extent can return a @got where
got->br_startoff < startoff.  In this case, xrep_cow_replace_range
replaces the entire mapping instead of just the part that had been
marked bad in the bitmap, but advances the bitmap cursor in
xrep_cow_replace by the amount replaced.  As a result, we fail to
replace the end of the bad range, and replace part of the good range.

Fix this by rewriting the replace method to handle replacing the middle
of a cow fork mapping.  This we do by returning both the current mapping
as @got, and the subset of the mapping that we want to replace as @rep,
using @rep to store the results of the new allocation, and comparing
@rep to @got to figure out the exact transformations needed.

Cc: stable@vger.kernel.org # v6.8
Fixes: dbbdbd0086 ("xfs: repair problems in CoW forks")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2026-08-03 11:22:08 +02:00
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