On Tue, 2023-10-17 at 13:29 -0400, Paul Moore wrote: > On Tue, Oct 17, 2023 at 1:09 PM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > On Tue, 2023-10-17 at 11:45 -0400, Paul Moore wrote: > > > On Tue, Oct 17, 2023 at 9:48 AM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > > > On Thu, 2023-10-05 at 12:32 +0200, Mickaël Salaün wrote: > > > > > > > > A complementary approach would be to create an > > > > > > > > LSM (or a dedicated interface) to tie certificate properties to a set of > > > > > > > > kernel usages, while still letting users configure these constraints. > > > > > > > > > > > > > > That is an interesting idea. Would the other security maintainers be in > > > > > > > support of such an approach? Would a LSM be the correct interface? > > > > > > > Some of the recent work I have done with introducing key usage and CA > > > > > > > enforcement is difficult for a distro to pick up, since these changes can be > > > > > > > viewed as a regression. Each end-user has different signing procedures > > > > > > > and policies, so making something work for everyone is difficult. Letting the > > > > > > > user configure these constraints would solve this problem. > > > > > > > > Something definitely needs to be done about controlling the usage of > > > > x509 certificates. My concern is the level of granularity. Would this > > > > be at the LSM hook level or even finer granaularity? > > > > > > You lost me, what do you mean by finer granularity than a LSM-based > > > access control? Can you give an existing example in the Linux kernel > > > of access control granularity that is finer grained than what is > > > provided by the LSMs? > > > > The current x509 certificate access control granularity is at the > > keyring level. Any key on the keyring may be used to verify a > > signature. Finer granularity could associate a set of certificates on > > a particular keyring with an LSM hook - kernel modules, BPRM, kexec, > > firmware, etc. Even finer granularity could somehow limit a key's > > signature verification to files in particular software package(s) for > > example. > > > > Perhaps Mickaël and Eric were thinking about a new LSM to control usage > > of x509 certificates from a totally different perspective. I'd like to > > hear what they're thinking. > > > > I hope this addressed your questions. > > Okay, so you were talking about finer granularity when compared to the > *current* LSM keyring hooks. Gotcha. > > If we need additional, or modified, hooks that shouldn't be a problem. > Although I'm guessing the answer is going to be moving towards > purpose/operation specific keyrings which might fit in well with the > current keyring level controls. I don't believe defining per purpose/operation specific keyrings will resolve the underlying problem of granularity. For example, different applications could be signed with different keys and should only be verified with the specific key. -- thanks, Mimi
