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Subject[PATCH] ima: namespacing IMA (PoC) - experimental
Date
This IMA namespacing patch set was initially implemented by Yuqiong Sun, 
while at IBM Research as a summer intern working with David Safford. It
was subsequently modified and rebased by Stefan Berger and Mehmet
Kayaalp. The resulting patches are being made available from the
"next-namespacing-experimental" branch on
https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
as a proof of concept, but will not be upstreamed.

Namespacing IMA is complex. It involves differentiating the IMA global
information (e.g. file hashes) from the IMA namespace specific
information (e.g. collected, measured, appraised). This information
needs to be created, updated, and freed as namespaces come and go, and
also freed when files are removed from the file system. In addition,
namespacing IMA properly also requires namespacing the securityfs files
(eg. policy, ascii/binary measurement lists), keyrings needed for
validating file signatures, and the hash table used to prevent the same
file from being measured multiple times within the same namespace, yet
separately in each namespace.

This requires some form of capability/permission checking. Currently,
only root with CAP_SYS_ADMIN permission is able to write securityfs
files and security xattrs. In addition, the IMA security xattrs need to
be namespace aware. (Other LSM subsystems are making similar changes.)

Like other initial subsystem namespacing, this IMA namespacing patch set
defines a new IMA namespace that is created with a new clone flag (this
needs to be changed). An unprivileged user can create an IMA namespace
in a new user namespace. The IMA securityfs policy file can be read and
set by a user with CAP_SYS_ADMIN within the user namespace, where the
IMA namespace is created. The policy can define the namespace
measurement and appraisal rules. Measurement is done recursively for
each nested IMA namespace. If the file to be measured is in policy for
multiple IMA namespaces, it is measured for each namespace. The list of
measurements are available to the CAP_SYS_ADMIN under the owner user
namespace. For appraisal, the non-init IMA namespaces use the "_ima"
session keyring. If the keyring is created and populated with keys,
these keys will be used for the appraisal rules defined in the policy of
the IMA namespace. Attestation for the IMA namespace is not supported in
this patchset.

For testing, we modified "runc" to create an IMA namespace and
initialized the policy and the keyring inside the container between the
clone() and exec() system calls. For accessing the IMA files in
securityfs inside the container, CAP_SYS_ADMIN is required to be added
to the list of capabilities in the config.json file. "runc" tries
loading the policy from /etc/default/ima-policy, and keys from
/etc/keys/ima/ inside the rootfs of the container. The runc patches are
available at the "imans" branch on https://github.com/stefanberger/runc.

Major changes include:
* Keyring creation is moved to userspace.
* Policy file is changed back from procfs to securityfs.
* Temporarily the IMA files are only accessible to CAP_SYS_ADMIN with
permissions set to user, group, and other.
* Patches should now be bisect-safe.

Regards,
Mehmet

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