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>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index f298c60f907d9ec559186fe4e9f2026730346fde..ca4588388fc30bca45887f0f9af9fb8422d9af7f 100644 (file)
--- 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));