netfilter: nfnetlink_acct: add filter support to nfacct counter list/reset

You can use this to skip accounting objects when listing/resetting
via NFNL_MSG_ACCT_GET/NFNL_MSG_ACCT_GET_CTRZERO messages with the
NLM_F_DUMP netlink flag. The filtering covers the following cases:

1. No filter specified. In this case, the client will get old behaviour,
2. List/reset counter object only: In this case, you have to use
NFACCT_F_QUOTA as mask and value 0.
3. List/reset quota objects only: You have to use NFACCT_F_QUOTA_PKTS
as mask and value - the same, for byte based quota mask should be
NFACCT_F_QUOTA_BYTES and value - the same.

If you want to obtain the object with any quota type
(ie. NFACCT_F_QUOTA_PKTS|NFACCT_F_QUOTA_BYTES), you need to perform
two dump requests, one to obtain NFACCT_F_QUOTA_PKTS objects and
another for NFACCT_F_QUOTA_BYTES.

Signed-off-by: Alexey Perevalov <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/nfnetlink_acct.h

···
 	NFACCT_USE,
 	NFACCT_FLAGS,
 	NFACCT_QUOTA,
+	NFACCT_FILTER,
 	__NFACCT_MAX
 };
 #define NFACCT_MAX (__NFACCT_MAX - 1)
 
+enum nfnl_attr_filter_type {
+	NFACCT_FILTER_UNSPEC,
+	NFACCT_FILTER_MASK,
+	NFACCT_FILTER_VALUE,
+	__NFACCT_FILTER_MAX
+};
+#define NFACCT_FILTER_MAX (__NFACCT_FILTER_MAX - 1)
 
 #endif /* _UAPI_NFNL_ACCT_H_ */

net/netfilter/nfnetlink_acct.c

···
 	char			data[0];
 };
 
+struct nfacct_filter {
+	u32 value;
+	u32 mask;
+};
+
 #define NFACCT_F_QUOTA (NFACCT_F_QUOTA_PKTS | NFACCT_F_QUOTA_BYTES)
 #define NFACCT_OVERQUOTA_BIT	2	/* NFACCT_F_OVERQUOTA */
 
···
 nfnl_acct_dump(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct nf_acct *cur, *last;
+	const struct nfacct_filter *filter = cb->data;
 
 	if (cb->args[2])
 		return 0;
···
 
 			last = NULL;
 		}
+
+		if (filter && (cur->flags & filter->mask) != filter->value)
+			continue;
+
 		if (nfnl_acct_fill_info(skb, NETLINK_CB(cb->skb).portid,
 				       cb->nlh->nlmsg_seq,
 				       NFNL_MSG_TYPE(cb->nlh->nlmsg_type),
···
 	return skb->len;
 }
 
+static int nfnl_acct_done(struct netlink_callback *cb)
+{
+	kfree(cb->data);
+	return 0;
+}
+
+static const struct nla_policy filter_policy[NFACCT_FILTER_MAX + 1] = {
+	[NFACCT_FILTER_MASK]	= { .type = NLA_U32 },
+	[NFACCT_FILTER_VALUE]	= { .type = NLA_U32 },
+};
+
+static struct nfacct_filter *
+nfacct_filter_alloc(const struct nlattr * const attr)
+{
+	struct nfacct_filter *filter;
+	struct nlattr *tb[NFACCT_FILTER_MAX + 1];
+	int err;
+
+	err = nla_parse_nested(tb, NFACCT_FILTER_MAX, attr, filter_policy);
+	if (err < 0)
+		return ERR_PTR(err);
+
+	filter = kzalloc(sizeof(struct nfacct_filter), GFP_KERNEL);
+	if (!filter)
+		return ERR_PTR(-ENOMEM);
+
+	filter->mask = ntohl(nla_get_be32(tb[NFACCT_FILTER_MASK]));
+	filter->value = ntohl(nla_get_be32(tb[NFACCT_FILTER_VALUE]));
+
+	return filter;
+}
+
 static int
 nfnl_acct_get(struct sock *nfnl, struct sk_buff *skb,
 	     const struct nlmsghdr *nlh, const struct nlattr * const tb[])
···
 	if (nlh->nlmsg_flags & NLM_F_DUMP) {
 		struct netlink_dump_control c = {
 			.dump = nfnl_acct_dump,
+			.done = nfnl_acct_done,
 		};
+
+		if (tb[NFACCT_FILTER]) {
+			struct nfacct_filter *filter;
+
+			filter = nfacct_filter_alloc(tb[NFACCT_FILTER]);
+			if (IS_ERR(filter))
+				return PTR_ERR(filter);
+
+			c.data = filter;
+		}
 		return netlink_dump_start(nfnl, skb, nlh, &c);
 	}
 
···
 	[NFACCT_PKTS] = { .type = NLA_U64 },
 	[NFACCT_FLAGS] = { .type = NLA_U32 },
 	[NFACCT_QUOTA] = { .type = NLA_U64 },
+	[NFACCT_FILTER] = {.type = NLA_NESTED },
 };
 
 static const struct nfnl_callback nfnl_acct_cb[NFNL_MSG_ACCT_MAX] = {