netdev - Re: [PATCH v20 17/23] LSM: security_secid_to

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Date:   Sat, 5 Sep 2020 23:11:21 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     casey.schaufler@...el.com, James Morris <jmorris@...ei.org>,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-audit@...hat.com, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        Stephen Smalley <sds@...ho.nsa.gov>, netdev@...r.kernel.org
Subject: Re: [PATCH v20 17/23] LSM: security_secid_to_secctx in netlink netfilter

On Wed, Aug 26, 2020 at 11:20 AM Casey Schaufler <casey@...aufler-ca.com> wrote:
>
> Change netlink netfilter interfaces to use lsmcontext
> pointers, and remove scaffolding.
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: John Johansen <john.johansen@...onical.com>
> Acked-by: Stephen Smalley <sds@...ho.nsa.gov>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> cc: netdev@...r.kernel.org
> ---
>  net/netfilter/nfnetlink_queue.c | 31 ++++++++++++-------------------
>  1 file changed, 12 insertions(+), 19 deletions(-)

...

> diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
> index d3f8e808c5d3..c830401f7792 100644
> --- a/net/netfilter/nfnetlink_queue.c
> +++ b/net/netfilter/nfnetlink_queue.c
> @@ -401,8 +399,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>         enum ip_conntrack_info ctinfo;
>         struct nfnl_ct_hook *nfnl_ct;
>         bool csum_verify;
> -       struct lsmcontext scaff; /* scaffolding */
> -       char *secdata = NULL;
> +       struct lsmcontext context = { };
>         u32 seclen = 0;
>
>         size = nlmsg_total_size(sizeof(struct nfgenmsg))
> @@ -469,7 +466,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>         }
>
>         if ((queue->flags & NFQA_CFG_F_SECCTX) && entskb->sk) {
> -               seclen = nfqnl_get_sk_secctx(entskb, &secdata);
> +               seclen = nfqnl_get_sk_secctx(entskb, &context);
>                 if (seclen)
>                         size += nla_total_size(seclen);
>         }

I think we can get rid of the local "seclen" variable, right?  We can
embed the nfqnl_get_sk_secctx() in the conditional and then simply
reference "context.len" everywhere else, yes?  For example:

  if (nfqnl_get_sk_secctx(..., &context))
    size += nla_total_size(context.len);

-- 
paul moore
www.paul-moore.com