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From:   Paul Moore <paul@paul-moore.com>
Date:   Wed, 9 May 2018 11:13:47 -0400
Message-ID: <CAHC9VhQKYt0PC0L65pwFRte1D98R=2tUDGxMVpc8bbJsMncGpw@mail.gmail.com>
Subject: Re: [PATCH ghak81 RFC V1 1/5] audit: normalize loginuid read access
To:     Richard Guy Briggs <rgb@redhat.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
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        <linux-security-module@vger.kernel.org>,
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        <linux-integrity@vger.kernel.org>,
        SElinux list <selinux@tycho.nsa.gov>,
        Eric Paris <eparis@redhat.com>,
        Steve Grubb <sgrubb@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        David Howells <dhowells@redhat.com>
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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.

>                 else
>                         audit_sig_uid = uid;
>                 security_task_getsecid(tsk, &audit_sig_sid);
> --
> 1.8.3.1

-- 
paul moore
www.paul-moore.com