linux-kernel - Re: [PATCH] tomoyo: Check exceeded quota early in tomoyo_domain_quota_is

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Date:   Tue, 14 Dec 2021 12:42:55 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     takedakn@...data.co.jp, jmorris@...ei.org, serge@...lyn.com,
        nogikh@...gle.com, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tomoyo: Check exceeded quota early in tomoyo_domain_quota_is_ok().

On Tue, 14 Dec 2021 at 12:36, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2021/12/14 18:45, Dmitry Vyukov wrote:
> > If tomoyo is used in a testing/fuzzing environment in learning mode,
> > for lots of domains the quota will be exceeded and stay exceeded
> > for prolonged periods of time. In such cases it's pointless (and slow)
> > to walk the whole acl list again and again just to rediscover that
> > the quota is exceeded. We already have the TOMOYO_DIF_QUOTA_WARNED flag
> > that notes the overflow condition. Check it early to avoid the slowdown.
>
> Thank you.
>
> This patch will make a slight but user visible change.
>
> When tomoyo_profile(domain->ns, domain->profile)->pref[TOMOYO_PREF_MAX_LEARNING_ENTRY] is
> increased (or domain->profile switches to a different profile which has larger
> pref[TOMOYO_PREF_MAX_LEARNING_ENTRY] value) after domain->flags[TOMOYO_DIF_QUOTA_WARNED] = true
> is called, tomoyo_domain_quota_is_ok() will continue returning "false", and ACLs are no longer
> appended.
>
> Therefore, administrator will have to manually do domain->flags[TOMOYO_DIF_QUOTA_WARNED] = false
> after increasing pref[TOMOYO_PREF_MAX_LEARNING_ENTRY] value (or changing domain->profile).
>
> But since the message
>
>   WARNING: Domain '%s' has too many ACLs to hold. Stopped learning mode.
>
> is a hint that tells administrator that "you will surely fail to try the enforcing mode on this
> domain because the kernel has failed to automatically append at least one ACL to this domain",
> administrator would have to retry the learning mode after increasing
> pref[TOMOYO_PREF_MAX_LEARNING_ENTRY] value (or changing domain->profile) even without this patch.
>
> Therefore, asking administrator to also clear domain->flags[TOMOYO_DIF_QUOTA_WARNED] after
> increasing pref[TOMOYO_PREF_MAX_LEARNING_ENTRY] value (or changing domain->profile) would be
> tolerable...

Should we reset flags[TOMOYO_DIF_QUOTA_WARNED] on any writes that
change TOMOYO_PREF_MAX_LEARNING_ENTRY?

If I am increasing TOMOYO_PREF_MAX_LEARNING_ENTRY because I observed
the warning, it's useful for me to receive the warning again.