Re: [PATCH v12 18/25] LSM: security_secid_to_secctx in netlink netfilter

[Stephen Smalley <sds@xxxxxxxxxxxxx>]

On 12/16/19 5:36 PM, Casey Schaufler wrote:
> Change netlink netfilter interfaces to use lsmcontext
> pointers, and remove scaffolding.
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> cc: netdev@xxxxxxxxxxxxxxx

Acked-by: Stephen Smalley <sds@xxxxxxxxxxxxx>

> ---
>   net/netfilter/nfnetlink_queue.c | 32 +++++++++++++-------------------
>   1 file changed, 13 insertions(+), 19 deletions(-)
>
> diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
> index 2d6668fd026c..a1296453d8f2 100644
> --- a/net/netfilter/nfnetlink_queue.c
> +++ b/net/netfilter/nfnetlink_queue.c
> @@ -301,12 +301,10 @@ static int nfqnl_put_sk_uidgid(struct sk_buff *skb, struct sock *sk)
>   	return -1;
>   }
>   
> -static u32 nfqnl_get_sk_secctx(struct sk_buff *skb, char **secdata)
> +static u32 nfqnl_get_sk_secctx(struct sk_buff *skb, struct lsmcontext *context)
>   {
> -	u32 seclen = 0;
>   #if IS_ENABLED(CONFIG_NETWORK_SECMARK)
>   	struct lsmblob blob;
> -	struct lsmcontext context = { };
>   
>   	if (!skb || !sk_fullsock(skb->sk))
>   		return 0;
> @@ -314,15 +312,16 @@ static u32 nfqnl_get_sk_secctx(struct sk_buff *skb, char **secdata)
>   	read_lock_bh(&skb->sk->sk_callback_lock);
>   
>   	if (skb->secmark) {
> +		/* Any LSM might be looking for the secmark */
>   		lsmblob_init(&blob, skb->secmark);
> -		security_secid_to_secctx(&blob, &context);
> -		*secdata = context.context;
> +		security_secid_to_secctx(&blob, context);
>   	}
>   
>   	read_unlock_bh(&skb->sk->sk_callback_lock);
> -	seclen = context.len;
> +	return context->len;
> +#else
> +	return 0;
>   #endif
> -	return seclen;
>   }
>   
>   static u32 nfqnl_get_bridge_size(struct nf_queue_entry *entry)
> @@ -398,8 +397,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>   	enum ip_conntrack_info uninitialized_var(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))
> @@ -466,7 +464,7 @@ 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);
>   	}
> @@ -601,7 +599,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>   	    nfqnl_put_sk_uidgid(skb, entskb->sk) < 0)
>   		goto nla_put_failure;
>   
> -	if (seclen && nla_put(skb, NFQA_SECCTX, seclen, secdata))
> +	if (seclen && nla_put(skb, NFQA_SECCTX, context.len, context.context))
>   		goto nla_put_failure;
>   
>   	if (ct && nfnl_ct->build(skb, ct, ctinfo, NFQA_CT, NFQA_CT_INFO) < 0)
> @@ -629,10 +627,8 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>   	}
>   
>   	nlh->nlmsg_len = skb->len;
> -	if (seclen) {
> -		lsmcontext_init(&scaff, secdata, seclen, 0);
> -		security_release_secctx(&scaff);
> -	}
> +	if (seclen)
> +		security_release_secctx(&context);
>   	return skb;
>   
>   nla_put_failure:
> @@ -640,10 +636,8 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
>   	kfree_skb(skb);
>   	net_err_ratelimited("nf_queue: error creating packet message\n");
>   nlmsg_failure:
> -	if (seclen) {
> -		lsmcontext_init(&scaff, secdata, seclen, 0);
> -		security_release_secctx(&scaff);
> -	}
> +	if (seclen)
> +		security_release_secctx(&context);
>   	return NULL;
>   }
>