Re: [RFC][PATCH] Smack<->Audit integration

Ahmed S. Darwish
2008-03-10T18:30:29Z

On Mon, Mar 10, 2008 at 09:07:08AM -0700, Casey Schaufler wrote:
>
> --- "Ahmed S. Darwish" <darwish.07@gmail.com> wrote:
>
...
> >
> > diff --git a/security/smack/smack.h b/security/smack/smack.h
> > index c444f48..2c8bb4c 100644
> > --- a/security/smack/smack.h
> > +++ b/security/smack/smack.h
> > @@ -57,6 +57,15 @@ struct inode_smack {
> > char *smk_inode; /* label of the fso */
> > struct mutex smk_lock; /* initialization lock */
> > int smk_flags; /* smack inode flags */
> > + int secid; /* security identifier */
>
> No.
>
> Secid's are horrid things and every effort should be made to
> expunge them from the known universe. Under no circumstances
> should thier use be expanded. The only reason Smack has them
> at all is because certain interfaces that in my mind should
> have known better use them. If you must deal with secids,
> and for this round of audit I think that's a given, use
> smack_to_secid(sp->smk_inode) where you need to. If there's a
> real performance issue apply intelligence to smack_to_secid
> instead of storing the secid. There ought to be a way to
> use container_of to do smack_to_secid, but I had trouble with
> that and moved along without figuring out what I had done
> wrong.
>

mm .. I should have remembered the un-official Smack motto:
"Everything is a label, and whenever possible, this label is allocated
once through system lifetime"

About performance, yes there'll be issues searching labels espicially
in audit_rule_match() which got called at the end of every system call.
I'll try it using container_of (it should work at the end).

...
>
> > @@ -1696,9 +1738,9 @@ static int smack_msg_queue_alloc_security(struct
> > msg_queue *msq)
> > */
> > static void smack_msg_queue_free_security(struct msg_queue *msq)
> > {
> > - struct kern_ipc_perm *kisp = &msq->q_perm;
> > + struct kern_ipc_perm *ipcp = &msq->q_perm;
> >
> > - kisp->security = NULL;
> > + kfree(ipcp->security);
> > }
>
> Don't you just hate repetative reviewers?
>

Probably hating secids with passion :) ?

Admittedly, after some thinking I felt now that they don't fit with
the Smack model very well.

...
> > +
> > +/**
> > + * smack_audit_rule_match - Audit given secid identified object ?
> > + * @secid: Security id to test
> > + * @field: Message flags given from user-space
> > + * @op: Required operation (only equality is allowed)
> > + * @vrule: Smack audit rule that will be checked against the secid object
> > + * @actx: audit context associated with the check (used for Audit logging)
> > + *
> > + * This is the core Audit hook. It's used to identify objects like
> > + * syscalls and inodes requested from user-space to be audited from
> > + * remaining kernel objects.
> > + */
> > +static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void *vrule,
> > + struct audit_context *actx)
> > +{
> > + struct smack_known *smk_rule = vrule;
>
> char *smack;
>

More of "everything is a label".

> > +
> > + if (!smk_rule) {
> > + audit_log(actx, GFP_KERNEL, AUDIT_SELINUX_ERR,
> > + "Smack: missing rule\n");
> > + return -ENOENT;
> > + }
> > +
> > + if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
> > + return 0;
> > +
>
> smack = smack_from_secid(secid);
>
> > + if (op == AUDIT_EQUAL)
> > + return (smk_rule->smk_secid == secid);
> > + if (op == AUDIT_NOT_EQUAL)
> > + return (smk_rule->smk_secid != secid);
>
> if (op == AUDIT_EQUAL)
> return (smk_rule->smk_smack == smack);
> if (op == AUDIT_NOT_EQUAL)
> return (smk_rule->smk_smack == smack);
>

You've meant using the short-circuit:
smk_rule->smk_smack == smack || strnmp(smack, ..., ..)
Right ?

...
> > +
> > +/**
> > + * smack_audit_rule_free - free internal audit rule representation
> > + * @vrule: rule to be freed.
> > + *
> > + * No memory was allocated in audit_rule_init.
> > + */
> > +static void smack_audit_rule_free(void *vrule)
> > +{
> > + /* No-op */
> > +}

This little no-op was the only thing that was agreed upon ;)

...
>
> Casey Schaufler
> casey@schaufler-ca.com

Regards,

--

"Better to light a candle, than curse the darkness"

Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com