Re: [RFC PATCH v2 2/4] [squash] do not store entry for SECSID_NULL

[Ondrej Mosnacek <omosnace@redhat.com>]

On Tue, Nov 27, 2018 at 5:58 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 11/27/18 5:36 AM, Ondrej Mosnacek wrote:
> > This patch is kept separate only for review. Eventually it will be
> > folded into the previous patch.
>
> This one triggers a lot of warnings (security_compute_av: unrecognized
> SID 0, security_sid_to_context_core: unrecognized SID 0) and some
> failures during selinux-testsuite inet_socket tests.  While the policy
> doesn't provide an entry for SECSID_NULL, the sidtab search logic was
> remapping it to the unlabeled context and that was apparently being
> relied upon by the labeled networking code IIUC.

You're right, I made a mistake in the sidtab_search_core() function -
it shouldn't just return NULL when sid == 0, but instead skip to the
default-to-unlabeled fallback. This will be easy to fix.

Thanks for testing!

I wonder why I didn't get any inet_socket failures when running the
testsuite myself... I will have to look at it closer tomorrow.

>
>
> >
> > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > ---
> >   security/selinux/ss/policydb.c |  2 +-
> >   security/selinux/ss/sidtab.c   | 25 ++++++++++++++++---------
> >   security/selinux/ss/sidtab.h   |  3 ++-
> >   3 files changed, 19 insertions(+), 11 deletions(-)
> >
> > diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
> > index 59359fa0bd74..a50d625e7946 100644
> > --- a/security/selinux/ss/policydb.c
> > +++ b/security/selinux/ss/policydb.c
> > @@ -912,7 +912,7 @@ int policydb_load_isids(struct policydb *p, struct sidtab *s)
> >                       sidtab_destroy(s);
> >                       goto out;
> >               }
> > -             if (c->sid[0] > SECINITSID_NUM) {
> > +             if (c->sid[0] == SECSID_NULL || c->sid[0] > SECINITSID_NUM) {
> >                       pr_err("SELinux:  Initial SID %s out of range.\n",
> >                               c->u.name);
> >                       sidtab_destroy(s);
> > diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> > index fd8115b211a6..e157d8240cf1 100644
> > --- a/security/selinux/ss/sidtab.c
> > +++ b/security/selinux/ss/sidtab.c
> > @@ -23,7 +23,7 @@ int sidtab_init(struct sidtab *s)
> >       if (!s->htable)
> >               return -ENOMEM;
> >
> > -     for (i = 0; i <= SECINITSID_NUM; i++)
> > +     for (i = 0; i < SECINITSID_NUM; i++)
> >               s->isids[i].set = 0;
> >
> >       for (i = 0; i < SIDTAB_SIZE; i++)
> > @@ -86,8 +86,15 @@ static int sidtab_insert(struct sidtab *s, u32 sid, struct context *context)
> >
> >   int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
> >   {
> > -     struct sidtab_isid_entry *entry = &s->isids[sid];
> > -     int rc = context_cpy(&entry->context, context);
> > +     struct sidtab_isid_entry *entry;
> > +     int rc;
> > +
> > +     if (sid == 0 || sid > SECINITSID_NUM)
> > +             return -EINVAL;
> > +
> > +     entry = &s->isids[sid - 1];
> > +
> > +     rc = context_cpy(&entry->context, context);
> >       if (rc)
> >               return rc;
> >
> > @@ -116,19 +123,19 @@ static struct context *sidtab_search_core(struct sidtab *s, u32 sid, int force)
> >       struct context *context;
> >       struct sidtab_isid_entry *entry;
> >
> > -     if (!s)
> > +     if (!s || sid == 0)
> >               return NULL;
> >
> >       if (sid > SECINITSID_NUM) {
> >               context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
> >       } else {
> > -             entry = &s->isids[sid];
> > +             entry = &s->isids[sid - 1];
> >               context = entry->set ? &entry->context : NULL;
> >       }
> >       if (context && (!context->len || force))
> >               return context;
> >
> > -     entry = &s->isids[SECINITSID_UNLABELED];
> > +     entry = &s->isids[SECINITSID_UNLABELED - 1];
> >       return entry->set ? &entry->context : NULL;
> >   }
> >
> > @@ -283,11 +290,11 @@ int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid)
> >       int rc;
> >       u32 i;
> >
> > -     for (i = 0; i <= SECINITSID_NUM; i++) {
> > +     for (i = 0; i < SECINITSID_NUM; i++) {
> >               struct sidtab_isid_entry *entry = &s->isids[i];
> >
> >               if (entry->set && context_cmp(context, &entry->context)) {
> > -                     *sid = i;
> > +                     *sid = i + 1;
> >                       return 0;
> >               }
> >       }
> > @@ -334,7 +341,7 @@ void sidtab_destroy(struct sidtab *s)
> >       if (!s)
> >               return;
> >
> > -     for (i = 0; i <= SECINITSID_NUM; i++)
> > +     for (i = 0; i < SECINITSID_NUM; i++)
> >               if (s->isids[i].set)
> >                       context_destroy(&s->isids[i].context);
> >
> > diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
> > index dc0a80bc8894..e657ae6bf996 100644
> > --- a/security/selinux/ss/sidtab.h
> > +++ b/security/selinux/ss/sidtab.h
> > @@ -36,7 +36,8 @@ struct sidtab {
> >       struct sidtab_node *cache[SIDTAB_CACHE_LEN];
> >       spinlock_t lock;
> >
> > -     struct sidtab_isid_entry isids[SECINITSID_NUM + 1];
> > +     /* index == SID - 1 (no entry for SECSID_NULL) */
> > +     struct sidtab_isid_entry isids[SECINITSID_NUM];
> >   };
> >
> >   int sidtab_init(struct sidtab *s);
> >
>

--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.