From 69cb8e9d8cd97cdf5e293b26d70a9dee3e35e6bd Mon Sep 17 00:00:00 2001
From: "Kiselev, Oleg" <okiselev@amazon.com>
Date: Wed, 20 Jul 2022 04:27:48 +0000
Subject: [PATCH] ext4: avoid resizing to a partial cluster size
Git-commit: 69cb8e9d8cd97cdf5e293b26d70a9dee3e35e6bd
Patch-mainline: v6.0-rc1
References: bsc#1206880

This patch avoids an attempt to resize the filesystem to an
unaligned cluster boundary.  An online resize to a size that is not
integral to cluster size results in the last iteration attempting to
grow the fs by a negative amount, which trips a BUG_ON and leaves the fs
with a corrupted in-memory superblock.

Signed-off-by: Oleg Kiselev <okiselev@amazon.com>
Link: https://lore.kernel.org/r/0E92A0AB-4F16-4F1A-94B7-702CC6504FDE@amazon.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/resize.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 5e3a893e600e..fea2a68d067b 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -2011,6 +2011,16 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
 	}
 	brelse(bh);
 
+	/*
+	 * For bigalloc, trim the requested size to the nearest cluster
+	 * boundary to avoid creating an unusable filesystem. We do this
+	 * silently, instead of returning an error, to avoid breaking
+	 * callers that blindly resize the filesystem to the full size of
+	 * the underlying block device.
+	 */
+	if (ext4_has_feature_bigalloc(sb))
+		n_blocks_count &= ~((1 << EXT4_CLUSTER_BITS(sb)) - 1);
+
 retry:
 	o_blocks_count = ext4_blocks_count(es);
 
-- 
2.35.3