Re: [AppArmor 00/45] AppArmor security module overview

John Johansen
2007-10-26T07:17:28Z

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On Thu, Oct 25, 2007 at 11:40:24PM -0700, jjohansen@suse.de wrote:
Sorry this got dropped some how.

This submission of the AppArmor security module is based against -mm.

Any comments and feedback to improve implementation are appreciated.

The patch series consists of five areas:

(1) Pass struct vfsmount through to LSM hooks.

(2) Fixes and improvements to __d_path():

(a) make it unambiguous and exclude unreachable paths from
/proc/mounts,

(b) make its result consistent in the face of remounts,

(c) introduce d_namespace_path(), a variant of d_path that goes up
to the namespace root instead of the chroot.

(d) the behavior of d_path() and getcwd() remain unchanged, and
there is no hidding of unreachable paths in /proc/mounts. The
patches addressing these have been seperated from the AppArmor
submission and will be introduced at a later date.

Part (a) has been in the -mm tree for a while; this series includes
an updated copy of the -mm patch. Parts (b) and (c) shouldn't be too
controversial.

(3) Be able to distinguish file descriptor access from access by name
in LSM hooks.

Applications expect different behavior from file descriptor
accesses and accesses by name in some cases. We need to pass this
information down the LSM hooks to allow AppArmor to tell which is
which.

(4) Convert the selinux sysctl pathname computation code into a standalone
function.

(5) The AppArmor LSM itself.

(See below.)

A tarball of the kernel patches, base user-space utilities, example
profiles, and technical documentation (including a walk-through) are
available at:

http://forgeftp.novell.com/apparmor/LKML_Submission-Oct-07/

Only the most recent features are covered in brief here for a more
complete explaination please refere to the technical documentation.

Changes since previous submission
- fix wrong error code for failed pathname
- fix change_profile ref counting bug
- fix change_hat missing mandatory profile bug
- file rules can now be specified in permission first order
- add append permission which is subset of write permission
- add lock mediation for finer grained control, previously locking only
required access right to a file
- added simple Network toggles for course network mediation
- added profile namespaces (currently only available through change_profile)
- added DAC style permissions
- added the ability to specify hard link rules using location pairs
- added per profile namespace default profile
- added pix transition mode
- builtin only

Outstanding Issues
- use of d_namespace_path and buffer allocation to obtain a pathname for
mediation.
- conditional passing of the vfsmnt. This can be addressed by rebasing
on the lookup intent patches but that has not been done for this
submission.
- ipc and signal mediation are a wip and not included.
- fine grained network mediation
- system confinement from boot is a wip and not included.
- documentation needs to be updated to include newest features

Explanation of new features

The user side policy parser now support specifying file rules with
permissions specified before the path expression; the old syntax is
still supported.

eg.
r /etc/shadow,

Profile Namespaces
AppArmor now allows for profile sets to exist in seperate namespaces.
This is the first step in allowing AppArmor to have different policy,
per container.

Profile namespaces currently can only be set through change_profile.
Confined tasks inherit the namespace of their parent.

User, Group, Other permission masks
AppArmor now allows file permissions to be specified at the user,
group, and other level similar to DAC. For each permission set of user,
group, other the full AppArmor permission set (rwaxlmk) are provided.
The permission group to apply is determined using the fsuid.

The permission sets are seperated using the : character. This deviates
from dac but the permission sets are wider, and do not have a set order.
If any distinct user:group:other permissions are being expressed then all
of the user:group:other permissions for the rule must be expressed. That
is to say just writing rw, does not provide user rw, and rw:r does not
provide user and group permissions.
eg.
/foo rw:r:r, # give user rw, group and other r
/foo rw::, # give user rw, no permissions to group and other
/foo :r:r, # give group and other read permissions
/foo ::r, # give other read permissions

Traditional AppArmor rules are still supported user side and are mapped
to the same permission in each of user, group and other. So
/foo rwpx,
is the same as
/foo rwpx:rwpx:rwpx,

For a given rule user, group, other must use the same exec qualifier.
Multiple rules can be used to specify different exec qualifiers for
each of user, group, or other for a given match.
eg.
/bin/foo px::,
/bin/foo :ix:ix,

The link permission is determined by the target files ownership this
allows for writting rules that enforce openwall style link restrictions.
/** l::, #allow linking to any file owned by the user

The user, group, other permission masks can be written in a permission
first manner as well.

Link rules
Dedicated link rules using source and destination have been added,
to allow for tighter control of hard links when necessary.
eg.
link /linkname -> /targetname,

if user:group:other link specification is desired then a user:group:other
mask containing only the link perm in the appropriate positions can be
specified. The permission group to apply is determined by the target
and the fsuid.
eg.
link l:: /linkname -> /targetname, # allow if /targetname owned by user
or
l:: /linkname -> /targetname,

Both the linkname and the target support full AppArmor globbing.
link l:: /** -> /**, # allow any link to target owned by user

Traditional AA style links are still supported and are mapped by the
parser into the newer link pair for the kernel.
/linkname rwl,
is mapped to
link /linkname -> /**,

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