linux-kernel - [PATCH 5.15 021/201] xfs: fix maxlevels comparisons in the btree staging code

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Date:   Wed, 27 Jul 2022 18:08:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Darrick J. Wong" <djwong@...nel.org>,
        Chandan Babu R <chandan.babu@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Leah Rumancik <leah.rumancik@...il.com>
Subject: [PATCH 5.15 021/201] xfs: fix maxlevels comparisons in the btree staging code

From: "Darrick J. Wong" <djwong@...nel.org>

[ Upstream commit 78e8ec83a404d63dcc86b251f42e4ee8aff27465 ]

The btree geometry computation function has an off-by-one error in that
it does not allow maximally tall btrees (nlevels == XFS_BTREE_MAXLEVELS).
This can result in repairs failing unnecessarily on very fragmented
filesystems.  Subsequent patches to remove MAXLEVELS usage in favor of
the per-btree type computations will make this a much more likely
occurrence.

Signed-off-by: Darrick J. Wong <djwong@...nel.org>
Reviewed-by: Chandan Babu R <chandan.babu@...cle.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Leah Rumancik <leah.rumancik@...il.com>
Acked-by: Darrick J. Wong <djwong@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/xfs/libxfs/xfs_btree_staging.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/xfs/libxfs/xfs_btree_staging.c
+++ b/fs/xfs/libxfs/xfs_btree_staging.c
@@ -662,7 +662,7 @@ xfs_btree_bload_compute_geometry(
 	xfs_btree_bload_ensure_slack(cur, &bbl->node_slack, 1);
 
 	bbl->nr_records = nr_this_level = nr_records;
-	for (cur->bc_nlevels = 1; cur->bc_nlevels < XFS_BTREE_MAXLEVELS;) {
+	for (cur->bc_nlevels = 1; cur->bc_nlevels <= XFS_BTREE_MAXLEVELS;) {
 		uint64_t	level_blocks;
 		uint64_t	dontcare64;
 		unsigned int	level = cur->bc_nlevels - 1;
@@ -724,7 +724,7 @@ xfs_btree_bload_compute_geometry(
 		nr_this_level = level_blocks;
 	}
 
-	if (cur->bc_nlevels == XFS_BTREE_MAXLEVELS)
+	if (cur->bc_nlevels > XFS_BTREE_MAXLEVELS)
 		return -EOVERFLOW;
 
 	bbl->btree_height = cur->bc_nlevels;