netfilter: nft_quota: dump consumed quota

Add a new attribute NFTA_QUOTA_CONSUMED that displays the amount of
quota that has been already consumed. This allows us to restore the
internal state of the quota object between reboots as well as to monitor
how wasted it is.

This patch changes the logic to account for the consumed bytes, instead
of the bytes that remain to be consumed.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -988,12 +988,14 @@ enum nft_quota_flags {
  *
  * @NFTA_QUOTA_BYTES: quota in bytes (NLA_U16)
  * @NFTA_QUOTA_FLAGS: flags (NLA_U32)
+ * @NFTA_QUOTA_CONSUMED: quota already consumed in bytes (NLA_U64)
  */
 enum nft_quota_attributes {
 	NFTA_QUOTA_UNSPEC,
 	NFTA_QUOTA_BYTES,
 	NFTA_QUOTA_FLAGS,
 	NFTA_QUOTA_PAD,
+	NFTA_QUOTA_CONSUMED,
 	__NFTA_QUOTA_MAX
 };
 #define NFTA_QUOTA_MAX		(__NFTA_QUOTA_MAX - 1)

net/netfilter/nft_quota.c

@@ -18,20 +18,20 @@
 struct nft_quota {
 	u64		quota;
 	bool		invert;
-	atomic64_t	remain;
+	atomic64_t	consumed;
 };
 
 static inline bool nft_overquota(struct nft_quota *priv,
-				 const struct nft_pktinfo *pkt)
+				 const struct sk_buff *skb)
 {
-	return atomic64_sub_return(pkt->skb->len, &priv->remain) < 0;
+	return atomic64_add_return(skb->len, &priv->consumed) >= priv->quota;
 }
 
 static inline void nft_quota_do_eval(struct nft_quota *priv,
 				     struct nft_regs *regs,
 				     const struct nft_pktinfo *pkt)
 {
-	if (nft_overquota(priv, pkt) ^ priv->invert)
+	if (nft_overquota(priv, pkt->skb) ^ priv->invert)
 		regs->verdict.code = NFT_BREAK;
 }
 
@@ -70,7 +70,7 @@ static int nft_quota_do_init(const struct nlattr * const tb[],
 
 	priv->quota = quota;
 	priv->invert = (flags & NFT_QUOTA_F_INV) ? true : false;
-	atomic64_set(&priv->remain, quota);
+	atomic64_set(&priv->consumed, 0);
 
 	return 0;
 }
@@ -86,9 +86,20 @@ static int nft_quota_obj_init(const struct nlattr * const tb[],
 static int nft_quota_do_dump(struct sk_buff *skb, const struct nft_quota *priv)
 {
 	u32 flags = priv->invert ? NFT_QUOTA_F_INV : 0;
+	u64 consumed;
+
+	consumed = atomic64_read(&priv->consumed);
+	/* Since we inconditionally increment consumed quota for each packet
+	 * that we see, don't go over the quota boundary in what we send to
+	 * userspace.
+	 */
+	if (consumed > priv->quota)
+		consumed = priv->quota;
 
 	if (nla_put_be64(skb, NFTA_QUOTA_BYTES, cpu_to_be64(priv->quota),
 			 NFTA_QUOTA_PAD) ||
+	    nla_put_be64(skb, NFTA_QUOTA_CONSUMED, cpu_to_be64(consumed),
+			 NFTA_QUOTA_PAD) ||
 	    nla_put_be32(skb, NFTA_QUOTA_FLAGS, htonl(flags)))
 		goto nla_put_failure;
 	return 0;