[RFC PATCH] lsm: add the inode_free_security_rcu() LSM implementation hook

[Mickaël Salaün]

On Tue, Jul 09, 2024 at 10:47:45PM -0400, Paul Moore wrote:
> On Tue, Jul 9, 2024 at 10:40 PM Paul Moore <paul at paul-moore.com> wrote:
> >
> > The LSM framework has an existing inode_free_security() hook which
> > is used by LSMs that manage state associated with an inode, but
> > due to the use of RCU to protect the inode, special care must be
> > taken to ensure that the LSMs do not fully release the inode state
> > until it is safe from a RCU perspective.
> >
> > This patch implements a new inode_free_security_rcu() implementation
> > hook which is called when it is safe to free the LSM's internal inode
> > state.  Unfortunately, this new hook does not have access to the inode
> > itself as it may already be released, so the existing
> > inode_free_security() hook is retained for those LSMs which require
> > access to the inode.
> >
> > Signed-off-by: Paul Moore <paul at paul-moore.com>
> > ---
> >  include/linux/lsm_hook_defs.h     |  1 +
> >  security/integrity/ima/ima.h      |  2 +-
> >  security/integrity/ima/ima_iint.c | 20 ++++++++------------
> >  security/integrity/ima/ima_main.c |  2 +-
> >  security/landlock/fs.c            |  9 ++++++---
> >  security/security.c               | 26 +++++++++++++-------------
> >  6 files changed, 30 insertions(+), 30 deletions(-)
> 
> FYI, this has only received "light" testing, and even that is fairly
> generous.  I booted up a system with IMA set to measure the TCB and
> ran through the audit and SELinux test suites; IMA seemed to be
> working just fine but I didn't poke at it too hard.  I didn't have an
> explicit Landlock test handy, but I'm hoping that the Landlock
> enablement on a modern Rawhide system hit it a little :)

If you want to test Landlock, you can do so like this:

cd tools/testing/selftests/landlock
make -C ../../../.. headers_install
make
for f in *_test; ./$f; done

...or you can build and run everything (on UML) with
`./check-linux build kselftest' provided here:
https://github.com/landlock-lsm/landlock-test-tools

...or, even simpler, you can run all checks by running
`./docker-run.sh debian/sid` for instance.

I need to update the kernel doc with these commands.

> 
> -- 
> paul-moore.com
>