On Tue, Dec 13, 2022 at 11:22 AM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > On Tue, Dec 13, 2022 at 10:00 AM Jeff Xu <jeffxu@xxxxxxxxxx> wrote: > > On Fri, Dec 9, 2022 at 10:29 AM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > > On Fri, Dec 9, 2022 at 11:05 AM <jeffxu@xxxxxxxxxxxx> wrote: > > > > > > > > From: Jeff Xu <jeffxu@xxxxxxxxxx> > > > > > > > > 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@xxxxxxxxxx> > > > > Reported-by: kernel test robot <lkp@xxxxxxxxx> > > > > --- > > > > 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 > -- > paul-moore.com
