[RFC PATCH v2 0/4] Fix ENOMEM errors during policy reload

[Ondrej Mosnacek <omosnace@redhat.com>]

This patchset is a second iteration of this patchset:
https://lore.kernel.org/selinux/20181113135255.26045-1-omosnace@redhat.com/T/

The patches that have "[squash]" in the subject are posted separately for ease
of review but will be folded into the previous patch in the final posting.

Changes in v2:
- dropped the first patch since it is already merged in -next
- fixed initial SID table to not reserve an entry for SECSID_NULL
- added back an equivalent of the reverse lookup cache
- fixed checkpatch.pl errors and some warnings

Notes on the reverse lookup cache:
I updated the sidtab insertion measurements [1] with data for the new patchset
(the difference being the cache addition) and I also measured the base code
with the reverse lookup cache removed [3] for comparison. Note that in this
case (adding a new context) the cache will never give a hit so this only
measures the overhead of traversing the whole cache. It seems that both cache
implementations have similar overhead, the new one being a bit slower (but it
has one entry more so it is expected).

I don't have any data on how the cache helps during regular reverse lookups,
since I couldn't come up with any good way to measure that.

Testing:
A Fedora 29 kernel with this patchset applied passes selinux-testsuite
and fixes GH issue #38 [2]. Additionaly, I decided to eat my own dog food and I
have now been running this kernel on my F29 work machine for several days. So
far everything runs smoothly and I haven't noticed any functional or
performance issues.

[1] https://docs.google.com/spreadsheets/d/e/2PACX-1vRUArNJR6kckm2SEs4dRZlijNVdCTmsNuWRGe7X3fC01YkBHpxXHnmcssxEiMF3Z7ivtXN2L5MC0ry-/pubhtml
[2] https://github.com/SELinuxProject/selinux-kernel/issues/38
[3] https://gitlab.com/omos/linux-public/commit/2c1ebcb8fbdcc6400734ba8d1c3015bd446e6fa5

Ondrej Mosnacek (4):
  selinux: use separate table for initial SID lookup
  [squash] do not store entry for SECSID_NULL
  selinux: overhaul sidtab to fix bug and improve performance
  [squash] add back reverse lookup cache to sidtab

 security/selinux/ss/mls.c      |  23 +-
 security/selinux/ss/mls.h      |   3 +-
 security/selinux/ss/policydb.c |  10 +-
 security/selinux/ss/services.c | 170 +++++----
 security/selinux/ss/services.h |   2 +-
 security/selinux/ss/sidtab.c   | 616 +++++++++++++++++++++------------
 security/selinux/ss/sidtab.h   |  95 +++--
 7 files changed, 560 insertions(+), 359 deletions(-)

-- 
2.19.1