[PATCH 3.13 152/162] ext4: fix overflow when updating superblock backups after resize

[Kamal Mostafa]

3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack at suse.cz>

commit 9378c6768e4fca48971e7b6a9075bc006eda981d upstream.

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
Signed-off-by: Jan Kara <jack at suse.cz>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Reviewed-by: Lukas Czerner <lczerner at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.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 14e0f8a..2400ad1 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1071,7 +1071,7 @@ 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));
-- 
1.9.1