[PATCH 5.4 368/389] ext4: avoid resizing to a partial cluster size

Greg Kroah-Hartman
2022-08-23T12:03:53Z

From: Kiselev, Oleg <okiselev@amazon.com>

[ Upstream commit 69cb8e9d8cd97cdf5e293b26d70a9dee3e35e6bd ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/resize.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 306003e29c4c..f0fc7fc579e6 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1979,6 +1979,16 @@ 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);

--
2.35.1