ext4: fix overflow when updating superblock backups after resize
commit 9378c676 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> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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