ext4: fix online resize's handling of a too-small final block group

commit f0a459dec5495a3580f8d784555e6f8f3bf7f263 upstream.

Avoid growing the file system to an extent so that the last block
group is too small to hold all of the metadata that must be stored in
the block group.

This problem can be triggered with the following reproducer:

umount /mnt
mke2fs -F -m0 -b 4096 -t ext4 -O resize_inode,^has_journal \
	-E resize=1073741824 /tmp/foo.img 128M
mount /tmp/foo.img /mnt
truncate --size 1708M /tmp/foo.img
resize2fs /dev/loop0 295400
umount /mnt
e2fsck -fy /tmp/foo.img

Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 823c0b82dfeb..41fb03718e87 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1956,6 +1956,26 @@ retry:
 		}
 	}
 
+	/*
+	 * Make sure the last group has enough space so that it's
+	 * guaranteed to have enough space for all metadata blocks
+	 * that it might need to hold.  (We might not need to store
+	 * the inode table blocks in the last block group, but there
+	 * will be cases where this might be needed.)
+	 */
+	if ((ext4_group_first_block_no(sb, n_group) +
+	     ext4_group_overhead_blocks(sb, n_group) + 2 +
+	     sbi->s_itb_per_group + sbi->s_cluster_ratio) >= n_blocks_count) {
+		n_blocks_count = ext4_group_first_block_no(sb, n_group);
+		n_group--;
+		n_blocks_count_retry = 0;
+		if (resize_inode) {
+			iput(resize_inode);
+			resize_inode = NULL;
+		}
+		goto retry;
+	}
+
 	/* extend the last group */
 	if (n_group == o_group)
 		add = n_blocks_count - o_blocks_count;