In order not to call copy_to_user (from fiemap_fill_next_extent)
we allocate memory in the kernel, fill it and copy it to user memory
after up_read(run_lock).

Reported-by: syzbot+36bb70085ef6edc2ebb9@syzkaller.appspotmail.com
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>