Add pam_cap.so "default=<IAB>" module argument support

Add a new optional argument to pam_cap.so. This argument substitutes
for a line like this in the capability.conf file:

  <IAB>       *

That is, it supplies the default <IAB> 3-tuple of capability vectors.
Any * value in the prevailing capability.conf file overrides this default.
However, the admin can supply arguments like this:

  auth pam_cap.so autoauth config=/dev/null default=^cap_wake_alarm

to grant everyone who executes it the ambient capability cap_wake_alarm.

This addresses:

  https://bugzilla.kernel.org/show_bug.cgi?id=213611

However, see:

  https://bugzilla.kernel.org/show_bug.cgi?id=212945

for issues limiting PAM application support for ambient capabilities in
general at present.

Signed-off-by: Andrew G. Morgan <[email protected]>
4 files changed