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Message-ID: <CAHC9VhQBuQ+yE1wmEYA4UcVwnRFXoyu9_4Qw5LWszUrkm_ornw@mail.gmail.com>
Date: Wed, 31 May 2023 18:13:55 -0400
From: Paul Moore <paul@...l-moore.com>
To: Christian Göttsche <cgzones@...glemail.com>
Cc: "Serge E. Hallyn" <serge@...lyn.com>, selinux@...r.kernel.org,
John Johansen <john.johansen@...onical.com>,
James Morris <jmorris@...ei.org>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Eric Paris <eparis@...isplace.org>,
Christian Brauner <brauner@...nel.org>,
Casey Schaufler <casey@...aufler-ca.com>,
Dave Chinner <dchinner@...hat.com>,
Nathan Lynch <nathanl@...ux.ibm.com>,
Al Viro <viro@...iv.linux.org.uk>,
Roberto Sassu <roberto.sassu@...wei.com>,
Micah Morton <mortonm@...omium.org>,
Frederick Lawler <fred@...udflare.com>,
Günther Noack <gnoack3000@...il.com>,
linux-kernel@...r.kernel.org, apparmor@...ts.ubuntu.com,
linux-security-module@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v4 1/9] capability: introduce new capable flag NODENYAUDIT
On Wed, May 31, 2023 at 2:34 PM Christian Göttsche
<cgzones@...glemail.com> wrote:
> On Wed, 31 May 2023 at 16:08, Serge E. Hallyn <serge@...lyn.com> wrote:
> >
> > On Wed, May 31, 2023 at 09:07:34AM -0500, Serge E. Hallyn wrote:
> > > On Thu, May 11, 2023 at 04:25:24PM +0200, Christian Göttsche wrote:
> > > > Introduce a new capable flag, CAP_OPT_NODENYAUDIT, to not generate
> > > > an audit event if the requested capability is not granted. This will be
> > > > used in a new capable_any() functionality to reduce the number of
> > > > necessary capable calls.
> > > >
> > > > Handle the flag accordingly in AppArmor and SELinux.
> > > >
> > > > Suggested-by: Paul Moore <paul@...l-moore.com>
> > > > Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> > >
> > > Reviewed-by: Serge Hallyn <serge@...lyn.com>
> >
> > Sorry, obviously I should have removed this, until the comment below was
> > answered :)
> >
> > > > ---
> > > > include/linux/security.h | 2 ++
> > > > security/apparmor/capability.c | 8 +++++---
> > > > security/selinux/hooks.c | 14 ++++++++------
> > > > 3 files changed, 15 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/include/linux/security.h b/include/linux/security.h
> > > > index e2734e9e44d5..629c775ec297 100644
> > > > --- a/include/linux/security.h
> > > > +++ b/include/linux/security.h
> > > > @@ -67,6 +67,8 @@ struct watch_notification;
> > > > #define CAP_OPT_NOAUDIT BIT(1)
> > > > /* If capable is being called by a setid function */
> > > > #define CAP_OPT_INSETID BIT(2)
> > > > +/* If capable should audit the security request for authorized requests only */
> > > > +#define CAP_OPT_NODENYAUDIT BIT(3)
> > > >
> > > > /* LSM Agnostic defines for security_sb_set_mnt_opts() flags */
> > > > #define SECURITY_LSM_NATIVE_LABELS 1
> > > > diff --git a/security/apparmor/capability.c b/security/apparmor/capability.c
> > > > index 326a51838ef2..98120dd62ca7 100644
> > > > --- a/security/apparmor/capability.c
> > > > +++ b/security/apparmor/capability.c
> > > > @@ -108,7 +108,8 @@ static int audit_caps(struct common_audit_data *sa, struct aa_profile *profile,
> > > > * profile_capable - test if profile allows use of capability @cap
> > > > * @profile: profile being enforced (NOT NULL, NOT unconfined)
> > > > * @cap: capability to test if allowed
> > > > - * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
> > > > + * @opts: CAP_OPT_NOAUDIT/CAP_OPT_NODENYAUDIT bit determines whether audit
> > > > + * record is generated
> > > > * @sa: audit data (MAY BE NULL indicating no auditing)
> > > > *
> > > > * Returns: 0 if allowed else -EPERM
> > > > @@ -126,7 +127,7 @@ static int profile_capable(struct aa_profile *profile, int cap,
> > > > else
> > > > error = -EPERM;
> > > >
> > > > - if (opts & CAP_OPT_NOAUDIT) {
> > > > + if ((opts & CAP_OPT_NOAUDIT) || ((opts & CAP_OPT_NODENYAUDIT) && error)) {
> > > > if (!COMPLAIN_MODE(profile))
> > > > return error;
> > > > /* audit the cap request in complain mode but note that it
> > > > @@ -142,7 +143,8 @@ static int profile_capable(struct aa_profile *profile, int cap,
> > > > * aa_capable - test permission to use capability
> > > > * @label: label being tested for capability (NOT NULL)
> > > > * @cap: capability to be tested
> > > > - * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
> > > > + * @opts: CAP_OPT_NOAUDIT/CAP_OPT_NODENYAUDIT bit determines whether audit
> > > > + * record is generated
> > > > *
> > > > * Look up capability in profile capability set.
> > > > *
> > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > > index 79b4890e9936..0730edf2f5f1 100644
> > > > --- a/security/selinux/hooks.c
> > > > +++ b/security/selinux/hooks.c
> > > > @@ -1571,7 +1571,7 @@ static int cred_has_capability(const struct cred *cred,
> > > > u16 sclass;
> > > > u32 sid = cred_sid(cred);
> > > > u32 av = CAP_TO_MASK(cap);
> > > > - int rc;
> > > > + int rc, rc2;
> > > >
> > > > ad.type = LSM_AUDIT_DATA_CAP;
> > > > ad.u.cap = cap;
> > > > @@ -1590,11 +1590,13 @@ static int cred_has_capability(const struct cred *cred,
> > > > }
> > > >
> > > > rc = avc_has_perm_noaudit(sid, sid, sclass, av, 0, &avd);
> > > > - if (!(opts & CAP_OPT_NOAUDIT)) {
> > > > - int rc2 = avc_audit(sid, sid, sclass, av, &avd, rc, &ad);
> > > > - if (rc2)
> > > > - return rc2;
> > > > - }
> > > > + if ((opts & CAP_OPT_NOAUDIT) || ((opts & CAP_OPT_NODENYAUDIT) && rc))
> > > > + return rc;
> > >
> > > Hm, if the caller passes only CAP_OPT_NODENYAUDIT, and rc == 0, then
> > > you will audit the allow. Is that what you want, or did you want, or
> > > did you want CAP_OPT_NODENYAUDIT to imply CAP_OPT_NOAUDIT?
> > >
>
> The new option should cause to issue an audit event if (and only if)
> the requested capability is in effect for the current task. If the
> task does not have the capability no audit event should be issued.
>
> The new option should not imply CAP_OPT_NOAUDIT since we want an audit
> event in the case the capability is in effect.
>
> I admit the naming is a bit confusing as CAP_OPT_NODENYAUDIT as well
> as the commit description contains a double negation (while the inline
> comment for the macro definition does not).
>
> Do you prefer naming the constant CAP_OPT_ALLOWAUDIT or CAP_OPT_AUDIT_ON_ALLOW?
I think we need a different name, although I'm struggling to think of
something ... I don't think ALLOWAUDIT is right, as I believe it
implies that it is needed to "allow" auditing to take place for the
operation. AUDIT_ON_ALLOW is better, but it still seems like it would
be required if you wanted to generate audit records on a successful
operation, which isn't correct. I think we need to focus on the idea
that the flag blocks auditing for denials.
CAP_OPT_NOAUDITDENY is pretty much what you have, but in my mind the
NOAUDITDENY shares enough with the existing NOAUDIT flag that it makes
a bit more sense.
I honestly don't know. However, whatever you pick, make sure you
update patch 2/X so that the name of ns_capable_nodenyaudit() is kept
close to the flag's name.
--
paul-moore.com
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