fsync() wants file descriptor
fsync() wants file descriptor

Also, truncate file before writing if the challenge length has
changed (became shorter) or garbage has otherwise been appended.

Yubico/yubico-pam,madrat-/yubico-pam,eworm-de/yubico-pam,eworm-de/yubico-pam,madrat-/yubico-pam,eworm-de/yubico-pam,madrat-/yubico-pam,Yubico/yubico-pam,Yubico/yubico-pam