From 5a9f8279988baa047d27092139cc08a0d120e330 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Wed, 5 Feb 2025 13:40:20 -0800
Subject: [PATCH] xfs: error out when a superblock buffer update reduces the
 agcount

commit b882b0f8138ffa935834e775953f1630f89bbb62 upstream.

XFS currently does not support reducing the agcount, so error out if
a logged sb buffer tries to shrink the agcount.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/xfs/xfs_buf_item_recover.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/xfs/xfs_buf_item_recover.c b/fs/xfs/xfs_buf_item_recover.c
index b9fd22891052..66a7e7201d17 100644
--- a/fs/xfs/xfs_buf_item_recover.c
+++ b/fs/xfs/xfs_buf_item_recover.c
@@ -713,6 +713,11 @@ xlog_recover_do_primary_sb_buffer(
 	 */
 	xfs_sb_from_disk(&mp->m_sb, dsb);
 
+	if (mp->m_sb.sb_agcount < orig_agcount) {
+		xfs_alert(mp, "Shrinking AG count in log recovery not supported");
+		return -EFSCORRUPTED;
+	}
+
 	/*
 	 * Initialize the new perags, and also update various block and inode
 	 * allocator setting based off the number of AGs or total blocks.