[PATCH v3 0/4] unverifiable file signatures

Mimi Zohar zohar at linux.vnet.ibm.com
Thu Mar 8 20:24:06 UTC 2018

For local filesystems, the kernel prevents files being executed from
being modified.  With IMA-measurement enabled, the kernel also emits
audit "time of measure, time of use" messages for files opened for
read, and subsequently opened for write.

Files on fuse are initially measured, appraised, and audited.  Although
the file data can change dynamically any time, making re-measuring,
re-appraising, or re-auditing pointless, this patch set attempts to
differentiate between unprivileged non-init root and privileged
mounted fuse filesystems.

This patch set addresses three different scenarios:
- Unprivileged non-init root mounted fuse filesystems are untrusted.
  Signature verification should always fail and re-measuring,
  re-appraising, re-auditing files makes no sense.

  Always enabled.

- For privileged mounted filesystems in a "secure" environment, with a
  correctly enforced security policy, which is willing to assume the
  inherent risk of specific fuse filesystems, it is reasonable to
  re-measure, re-appraise, and re-audit files.

  Enabled by default to prevent breaking existing systems.

- Privileged mounted filesystems unwilling to assume the risks and
  prefers to securely fail safe.

  Enabled based on policy.

Changelog v3:
- Rename the builtin policy name to "fail_securely".


Mimi Zohar (4):
  ima: fail file signature verification on non-init mounted filesystems
  ima: re-evaluate files on privileged mounted filesystems
  ima: fail signature verification based on policy
  fuse: define the filesystem as untrusted

 Documentation/admin-guide/kernel-parameters.txt |  8 +++++++-
 fs/fuse/inode.c                                 |  3 +++
 include/linux/fs.h                              |  2 ++
 security/integrity/ima/ima_appraise.c           | 16 +++++++++++++++-
 security/integrity/ima/ima_main.c               | 14 ++++++++++++--
 security/integrity/ima/ima_policy.c             |  5 +++++
 security/integrity/integrity.h                  |  1 +
 7 files changed, 45 insertions(+), 4 deletions(-)


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