On Tue, Dec 13, 2022 at 11:22 AM Paul Moore paul@paul-moore.com wrote:
On Tue, Dec 13, 2022 at 10:00 AM Jeff Xu jeffxu@google.com wrote:
On Fri, Dec 9, 2022 at 10:29 AM Paul Moore paul@paul-moore.com wrote:
On Fri, Dec 9, 2022 at 11:05 AM jeffxu@chromium.org wrote:
From: Jeff Xu jeffxu@google.com
The new security_memfd_create allows lsm to check flags of memfd_create.
The security by default system (such as chromeos) can use this to implement system wide lsm to allow only non-executable memfd being created.
Signed-off-by: Jeff Xu jeffxu@google.com Reported-by: kernel test robot lkp@intel.com
include/linux/lsm_hook_defs.h | 1 + include/linux/lsm_hooks.h | 4 ++++ include/linux/security.h | 6 ++++++ mm/memfd.c | 5 +++++ security/security.c | 5 +++++ 5 files changed, 21 insertions(+)
We typically require at least one in-tree LSM implementation to accompany a new LSM hook. Beyond simply providing proof that the hook has value, it helps provide a functional example both for reviewers as well as future LSM implementations. Also, while the BPF LSM is definitely "in-tree", its nature is such that the actual implementation lives out-of-tree; something like SELinux, AppArmor, Smack, etc. are much more desirable from an in-tree example perspective.
Thanks for the comments. Would that be OK if I add a new LSM in the kernel to block executable memfd creation ?
If you would be proposing the LSM only to meet the requirement of providing an in-tree LSM example, no that would definitely *not* be okay.
Proposing a new LSM involves documenting a meaningful security model, implementing it, developing tests, going through a (likely multi-step) review process, and finally accepting the long term maintenance responsibilities of this new LSM. If you are proposing a new LSM because you feel the current LSMs do not provide a security model which meets your needs, then yes, proposing a new LSM might be a good idea. However, if you are proposing a new LSM because you don't want to learn how to add a new hook to an existing LSM, then I suspect you are misguided/misinformed with the amount of work involved in submitting a new LSM.
Alternatively, it might be possible to add this into SELinux or landlock, it will be a larger change.
It will be a much smaller change than submitting a new LSM, and it would have infinitely more value to the community than a throw-away LSM where the only use-case is getting your code merged upstream.
Thanks, my original thought is this LSM will be used by ChromeOS, since all of its memfd shall be non-executable. That said, I see the community will benefit more with this in SELinux.
I will work to add this in SELinux, appreciate help while I'm learning to add this.
Jeff
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