[PATCH 1/1] su: Add a delay if the password is incorrect

[Laurent Bercot]

On 16/03/2014 03:06, Rich Felker wrote:
> /tmp is not suitable for this; you can never assume the ability to
> create a fixed-name file in /tmp, since the namespace of /tmp is
> shared on a first-come, first-served basis. Any programs using /tmp
> except for creating randomly-named files there are buggy.

  Hm, indeed. Unix/FHS/whatever lacks a guaranteed writable and
boot-time-available directory just for root.
  / is not guaranteed writable, and should not be.
  /var/* is not guaranteed available at boot time.
  /tmp is not reserved to root.
  I have such a directory on my systems (/mnt/tmpfs, 0755, with /tmp
actually being a symlink to /mnt/tmpfs/tmp, 1777). Some distributions
use an initramfs and create /lib/rw (ugh). Unfortunately, nothing is
standardized... Maybe we could use /dev ? Ha ha, only serious.


> It would probably be suitable to skip the check if the appropriate
> directory under /var does not exist (but not just if opening it fails
> for a reason other than non-existence, since you don't want, e.g.,
> fd-exhaustion attacks to let an attacked bypass the rate-limiting).

  In the absence of a suitable directory other than /var/*, this is
probably the best solution.

-- 
  Laurent