KASAN: slab-out-of-bounds Write in __ext4_expand_extra_isize

Hello, syzbot found the following crash on: HEAD commit:a880148cb2af Add linux-next specific files for 20180831 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=135f5e0a40 kernel config: https://syzkaller.appspot.com/x/.config?x=a059d319ef7d83f6

KASAN: slab-out-of-bounds Write in __ext4_expand_extra_isize

Hello, syzbot found the following crash on: HEAD commit:a880148cb2af Add linux-next specific files for 20180831 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=135f5e0a40 kernel config: https://syzkaller.appspot.com/x/.config?x=a059d319ef7d83f6