Re: TOMOYO's pull request for v6.12

["Serge E. Hallyn" <serge@hallyn.com>]

On Wed, Oct 02, 2024 at 09:43:07PM -0500, Serge E. Hallyn wrote:
> On Wed, Oct 02, 2024 at 04:12:50PM -0400, Paul Moore wrote:
> > Hi all,
> > 
> > Hopefully by now you've at least seen the TOMOYO v6.12 pull request
> > thread; if you haven't read it yet, I suggest you do so before reading
> > the rest of this mail:
> > 
> > https://lore.kernel.org/all/0c4b443a-9c72-4800-97e8-a3816b6a9ae2@I-love.SAKURA.ne.jp
> > 
> > Of the three commits in the pull request, the commit which concerns me
> > the most is 8b985bbfabbe ("tomoyo: allow building as a loadable LSM
> > module").  The commit worries me as it brings management of the TOMOYO
> > LSM callbacks into TOMOYO itself, overriding the LSM framework.
> > Jonathan raises a similar point, although his issue is more focused on
> > the symbol export approach itself, rather than conceptual issues
> > relating to the LSM framework.  I will admit there are some high level
> > similarities to this approach and the BPF LSM, but I believe we can
> > say that the BPF LSM exception is necessary due to the nature of BPF,
> > and not something we want to see duplicated outside of that one
> > special case.
> > 
> > As I wrote in my original response to this pull request, this is not
> > something I would accept in a new LSM submission and thus I feel
> > compelled to speak out against this change and submit a revert to
> > Linus.  However, as the LSM framework exists to satisfy the needs of
> > the individual LSMs, I've tried to ensure that significant changes
> > like these are done with support of the majority of LSMs.  I
> > understand that in a case like this, reverting LSM-specific commits,
> > individual LSM maintainers may not want to speak up on the issue so
> > I'm going to let this message sit on-list until Friday morning, unless
> > I see the majority of the LSMs voicing support *against* reverting the
> > TOMOYO commit above (and the other related commit) I will proceed with
> > submitting the revert to Linus on Friday.  I would prefer if all
> > responses are sent on-list, but you can also mail me privately with
> > your objection to the revert and I will include it in the count.
> > 
> > Thanks.
> 
> Huh!  Honestly, when I read the thread, especially Jon's comments, I was
> worried.  But getting a chance to look at the patch now, it actually
> seems good to me.  No one is getting affected unless they enable
> CONFIG_TOMOYO_LKM.  Even those distros which have been enabling TOMOYO
> won't be exporting new hooks without a config change, iiuc.
> 
> -serge

OTOH I am worried about the threatening sentence:

> This backdoor symbol-export mechanism is a transitional hack needed for
> demonstrating that loadable LSM can work. This hack will be replaced with
> proper symbol-export via appropriate trees after this merge window closes.


(in 7dce903c-2f76-43b2-bb6f-808cb50d0696@I-love.SAKURA.ne.jp)

-serge