From: "Darrick J. Wong" <djwong@kernel.org> stable inclusion from stable-v5.10.251 commit f3c0d1fc1eadbb4adbee5ab7757d41d35f48325b category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14733 CVE: CVE-2026-43187 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=t... -------------------------------- [ Upstream commit 6f13c1d2a6271c2e73226864a0e83de2770b6f34 ] Back in commit 2a2b5932db6758 ("xfs: fix attr leaf header freemap.size underflow"), Brian Foster observed that it's possible for a small freemap at the end of the end of the xattr entries array to experience a size underflow when subtracting the space consumed by an expansion of the entries array. There are only three freemap entries, which means that it is not a complete index of all free space in the leaf block. This code can leave behind a zero-length freemap entry with a nonzero base. Subsequent setxattr operations can increase the base up to the point that it overlaps with another freemap entry. This isn't in and of itself a problem because the code in _leaf_add that finds free space ignores any freemap entry with zero size. However, there's another bug in the freemap update code in _leaf_add, which is that it fails to update a freemap entry that begins midway through the xattr entry that was just appended to the array. That can result in the freemap containing two entries with the same base but different sizes (0 for the "pushed-up" entry, nonzero for the entry that's actually tracking free space). A subsequent _leaf_add can then allocate xattr namevalue entries on top of the entries array, leading to data loss. But fixing that is for later. For now, eliminate the possibility of confusion by zeroing out the base of any freemap entry that has zero size. Because the freemap is not intended to be a complete index of free space, a subsequent failure to find any free space for a new xattr will trigger block compaction, which regenerates the freemap. It looks like this bug has been in the codebase for quite a long time. Cc: <stable@vger.kernel.org> # v2.6.12 Fixes: 1da177e4c3f415 ("Linux-2.6.12-rc2") Signed-off-by: "Darrick J. Wong" <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Long Li <leo.lilong@huawei.com> --- fs/xfs/libxfs/xfs_attr_leaf.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c index e953bc44d4d0..3954bf017c8d 100644 --- a/fs/xfs/libxfs/xfs_attr_leaf.c +++ b/fs/xfs/libxfs/xfs_attr_leaf.c @@ -1575,6 +1575,19 @@ xfs_attr3_leaf_add_work( min_t(uint16_t, ichdr->freemap[i].size, sizeof(xfs_attr_leaf_entry_t)); } + + /* + * Don't leave zero-length freemaps with nonzero base lying + * around, because we don't want the code in _remove that + * matches on base address to get confused and create + * overlapping freemaps. If we end up with no freemap entries + * then the next _add will compact the leaf block and + * regenerate the freemaps. + */ + if (ichdr->freemap[i].size == 0 && ichdr->freemap[i].base > 0) { + ichdr->freemap[i].base = 0; + ichdr->holes = 1; + } } ichdr->usedbytes += xfs_attr_leaf_entsize(leaf, args->index); return 0; -- 2.52.0