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Date:   Thu, 10 May 2018 17:21:14 -0400
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
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        Eric Paris <eparis@redhat.com>,
        Steve Grubb <sgrubb@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        David Howells <dhowells@redhat.com>
Subject: Re: [PATCH ghak81 RFC V1 1/5] audit: normalize loginuid read access
Message-ID: <20180510212114.pefeyw5cuqlmjewp@madcap2.tricolour.ca>
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On 2018-05-09 11:13, Paul Moore wrote:
> On Fri, May 4, 2018 at 4:54 PM, Richard Guy Briggs <rgb@redhat.com> wrote:
> > Recognizing that the loginuid is an internal audit value, use an access
> > function to retrieve the audit loginuid value for the task rather than
> > reaching directly into the task struct to get it.
> >
> > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > ---
> >  kernel/auditsc.c | 16 ++++++++--------
> >  1 file changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index 479c031..f3817d0 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -374,7 +374,7 @@ static int audit_field_compare(struct task_struct *tsk,
> >         case AUDIT_COMPARE_EGID_TO_OBJ_GID:
> >                 return audit_compare_gid(cred->egid, name, f, ctx);
> >         case AUDIT_COMPARE_AUID_TO_OBJ_UID:
> > -               return audit_compare_uid(tsk->loginuid, name, f, ctx);
> > +               return audit_compare_uid(audit_get_loginuid(tsk), name, f, ctx);
> >         case AUDIT_COMPARE_SUID_TO_OBJ_UID:
> >                 return audit_compare_uid(cred->suid, name, f, ctx);
> >         case AUDIT_COMPARE_SGID_TO_OBJ_GID:
> > @@ -385,7 +385,7 @@ static int audit_field_compare(struct task_struct *tsk,
> >                 return audit_compare_gid(cred->fsgid, name, f, ctx);
> >         /* uid comparisons */
> >         case AUDIT_COMPARE_UID_TO_AUID:
> > -               return audit_uid_comparator(cred->uid, f->op, tsk->loginuid);
> > +               return audit_uid_comparator(cred->uid, f->op, audit_get_loginuid(tsk));
> >         case AUDIT_COMPARE_UID_TO_EUID:
> >                 return audit_uid_comparator(cred->uid, f->op, cred->euid);
> >         case AUDIT_COMPARE_UID_TO_SUID:
> > @@ -394,11 +394,11 @@ static int audit_field_compare(struct task_struct *tsk,
> >                 return audit_uid_comparator(cred->uid, f->op, cred->fsuid);
> >         /* auid comparisons */
> >         case AUDIT_COMPARE_AUID_TO_EUID:
> > -               return audit_uid_comparator(tsk->loginuid, f->op, cred->euid);
> > +               return audit_uid_comparator(audit_get_loginuid(tsk), f->op, cred->euid);
> >         case AUDIT_COMPARE_AUID_TO_SUID:
> > -               return audit_uid_comparator(tsk->loginuid, f->op, cred->suid);
> > +               return audit_uid_comparator(audit_get_loginuid(tsk), f->op, cred->suid);
> >         case AUDIT_COMPARE_AUID_TO_FSUID:
> > -               return audit_uid_comparator(tsk->loginuid, f->op, cred->fsuid);
> > +               return audit_uid_comparator(audit_get_loginuid(tsk), f->op, cred->fsuid);
> >         /* euid comparisons */
> >         case AUDIT_COMPARE_EUID_TO_SUID:
> >                 return audit_uid_comparator(cred->euid, f->op, cred->suid);
> > @@ -611,7 +611,7 @@ static int audit_filter_rules(struct task_struct *tsk,
> >                                 result = match_tree_refs(ctx, rule->tree);
> >                         break;
> >                 case AUDIT_LOGINUID:
> > -                       result = audit_uid_comparator(tsk->loginuid, f->op, f->uid);
> > +                       result = audit_uid_comparator(audit_get_loginuid(tsk), f->op, f->uid);
> >                         break;
> >                 case AUDIT_LOGINUID_SET:
> >                         result = audit_comparator(audit_loginuid_set(tsk), f->op, f->val);
> > @@ -2287,8 +2287,8 @@ int audit_signal_info(int sig, struct task_struct *t)
> >             (sig == SIGTERM || sig == SIGHUP ||
> >              sig == SIGUSR1 || sig == SIGUSR2)) {
> >                 audit_sig_pid = task_tgid_nr(tsk);
> > -               if (uid_valid(tsk->loginuid))
> > -                       audit_sig_uid = tsk->loginuid;
> > +               if (uid_valid(audit_get_loginuid(tsk)))
> > +                       audit_sig_uid = audit_get_loginuid(tsk);
> 
> I realize this comment is a little silly given the nature of loginuid,
> but if we are going to abstract away loginuid accesses (which I think
> is good), we should probably access it once, store it in a local
> variable, perform the validity check on the local variable, then
> commit the local variable to audit_sig_uid.  I realize a TOCTOU
> problem is unlikely here, but with this new layer of abstraction it
> seems that some additional safety might be a good thing.

Ok, I'll just assign it to where it is going and check it there, holding
the audit_ctl_lock the whole time, since it should have been done
anyways for all of audit_sig_{pid,uid,sid} anyways to get a consistent
view from the AUDIT_SIGNAL_INFO fetch.

> >                 else
> >                         audit_sig_uid = uid;
> >                 security_task_getsecid(tsk, &audit_sig_sid);

> paul moore

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635