Re: [PATCH v3 20/24] LSM: security_secid_to_secctx in netlink netfilter

[Kees Cook <keescook@chromium.org>]

On Fri, Jun 21, 2019 at 11:52:29AM -0700, Casey Schaufler wrote:
> Change netlink netfilter interfaces to use lsmcontext
> pointers, and remove scaffolding.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  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 6da00c7add5b..69efb688383f 100644
> --- a/net/netfilter/nfnetlink_queue.c
> +++ b/net/netfilter/nfnetlink_queue.c
> @@ -305,12 +305,10 @@ 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;
> @@ -318,15 +316,16 @@ 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)
> @@ -402,8 +401,7 @@ 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))
> @@ -470,7 +468,7 @@ 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);
>  	}
> @@ -605,7 +603,7 @@ 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)
> @@ -633,10 +631,8 @@ 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:
> @@ -644,10 +640,8 @@ 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;
>  }
>  
> -- 
> 2.20.1
> 

-- 
Kees Cook