From 9378c6768e4fca48971e7b6a9075bc006eda981d Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Thu, 30 Oct 2014 10:52:57 -0400
Subject: [PATCH] ext4: fix overflow when updating superblock backups after
 resize

When there are no meta block groups update_backups() will compute the
backup block in 32-bit arithmetics thus possibly overflowing the block
number and corrupting the filesystem. OTOH filesystems without meta
block groups larger than 16 TB should be rare. Fix the problem by doing
the counting in 64-bit arithmetics.

Coverity-id: 741252
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
---
 fs/ext4/resize.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index f298c60f907d9..ca4588388fc30 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1081,7 +1081,7 @@ static void update_backups(struct super_block *sb, int blk_off, char *data,
 			break;
 
 		if (meta_bg == 0)
-			backup_block = group * bpg + blk_off;
+			backup_block = ((ext4_fsblk_t)group) * bpg + blk_off;
 		else
 			backup_block = (ext4_group_first_block_no(sb, group) +
 					ext4_bg_has_super(sb, group));
-- 
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