ext4: fix overflow when updating superblock backups after resize

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@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 14e0f8a25c81a3ed9df1563fe372ed4bc29f7eaf..2400ad1c3d121b59fd36a30a31698c9a1d5529e2 100644 (file)
--- 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));