From 742255d914bf06fa8e8a3f048aae2c738657af52 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Fri, 2 Oct 2020 14:47:25 -0400
Subject: [PATCH 11/46] resize2fs: prevent block group descriptors from
 overflowing the first bg
Content-Type: text/plain

For 1k block file systems, resizing a file system larger than
1073610752 blocks will result in the size of the block group
descriptors to be so large that it will overlap with the backup
superblock in block group #1.   This problem can be reproduced via:

    mke2fs -t ext4 /tmp/foo.img 200M
    resize2fs /tmp/foo.img 1T
    e2fsck -f /tmp/foo.img

https://github.com/tytso/e2fsprogs/issues/50

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
---
 resize/main.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/resize/main.c b/resize/main.c
index a0c31c06..5e771d2a 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -269,6 +269,8 @@ int main (int argc, char ** argv)
 	long		sysval;
 	int		len, mount_flags;
 	char		*mtpt, *undo_file = NULL;
+	dgrp_t		new_group_desc_count;
+	unsigned long	new_desc_blocks;
 
 #ifdef ENABLE_NLS
 	setlocale(LC_MESSAGES, "");
@@ -528,6 +530,18 @@ int main (int argc, char ** argv)
 			exit(1);
 		}
 	}
+	new_group_desc_count = ext2fs_div64_ceil(new_size -
+				fs->super->s_first_data_block,
+						 EXT2_BLOCKS_PER_GROUP(fs->super));
+	new_desc_blocks = ext2fs_div_ceil(new_group_desc_count,
+					  EXT2_DESC_PER_BLOCK(fs->super));
+	if ((new_desc_blocks + fs->super->s_first_data_block) >
+	    EXT2_BLOCKS_PER_GROUP(fs->super)) {
+		com_err(program_name, 0,
+			_("New size results in too many block group "
+			  "descriptors.\n"));
+		exit(1);
+	}
 
 	if (!force && new_size < min_size) {
 		com_err(program_name, 0,
-- 
2.35.1