[PATCH v4 00/23] LSM: Module stacking for AppArmor

[Casey Schaufler <casey@schaufler-ca.com>]

This patchset provides the changes required for
the AppArmor security module to stack safely with any other.

Because of the changes to slot handling and the rework of
"display" I have not included the Reviewed-by tags from the
previous version.

v4: Incorporate feedback from v3
    - Mark new lsm_<blob>_alloc functions static
    - Replace the lsm and slot fields of the security_hook_list
      with a pointer to a LSM allocated lsm_id structure. The
      LSM identifies if it needs a slot explicitly. Use the
      lsm_id rather than make security_add_hooks return the
      slot value.
    - Validate slot values used in security.c
    - Reworked the "display" process attribute handling so that
      it works right and doesn't use goofy list processing.
    - fix display value check in dentry_init_security
    - Replace audit_log of secids with '?' instead of deleting
      the audit log

v3: Incorporate feedback from v2
    - Make lsmblob parameter and variable names more
      meaningful, changing "le" and "l" to "blob".
    - Improve consistency of constant naming.
    - Do more sanity checking during LSM initialization.
    - Be a bit clearer about what is temporary scaffolding.
    - Rather than clutter security_getpeersec_dgram with
      otherwise unnecessary checks remove the apparmor
      stub, which does nothing useful.

Patches 0001-0003 complete the process of moving managment
of security blobs that might be shared from the individual
modules to the infrastructure.

Patches 0004-0014 replace system use of a "secid" with
a structure "lsmblob" containing information from the
security modules to be held and reused later. At this
point lsmblob contains an array of u32 secids, one "slot"
for each of the security modules compiled into the
kernel that used secids. A "slot" is allocated when
a security module requests one.
The infrastructure is changed to use the slot number
to pass the correct secid to or from the security module
hooks.

It is important that the lsmblob be a fixed size entity
that does not have to be allocated. Several of the places
where it is used would have performance and/or locking
issues with dynamic allocation.

Patch 0015 provides a mechanism for a process to
identify which security module's hooks should be used
when displaying or converting a security context string.
A new interface /proc/.../attr/display contains the name
of the security module to show. Reading from this file
will present the name of the module, while writing to
it will set the value. Only names of active security
modules are accepted. Internally, the name is translated
to the appropriate "slot" number for the module which
is then stored in the task security blob.

Patch 0016 Starts the process of changing how a security
context is represented. Since it is possible for a
security context to have been generated by more than one
security module it is now necessary to note which module
created a security context so that the correct "release"
hook can be called. There are several places where the
module that created a security context cannot be inferred.

This is achieved by introducing a "lsmcontext" structure
which contains the context string, its length and the
"slot" number of the security module that created it.
The security_release_secctx() interface is changed,
replacing the (string,len) pointer pair with a lsmcontext
pointer.

Patches 0012-0021 convert the security interfaces from
(string,len) pointer pairs to a lsmcontext pointer.
The slot number identifying the creating module is
added by the infrastructure. Where the security context
is stored for extended periods the data type is changed.

The Netlabel code is converted to save lsmblob structures
instead of secids in Patch 0022.

Finally, with all interference on the AppArmor hooks
removed, Patch 0023 removes the exclusive bit from
AppArmor. An unnecessary stub hook was also removed.

The Ubuntu project is using an earlier version of
this patchset in their distribution to enable stacking
for containers.

Performance measurements to date have the change
within the "noise". Better benchmarks are in the
works.

https://github.com/cschaufler/lsm-stacking.git#stack-5.2-v4-apparmor

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---