quota匹配帮助信息如下。

# iptables -m quota -h
quota match options:
[!] --quota quota               quota (bytes)

如下,当主机192.168.1.111发送的报文总量超过1024000字节之后,阻断其报文。

# iptables -t filter -I INPUT -p tcp -s 192.168.1.105 -m quota --quota 1024000 -j ACCEPT
# iptables -t filter -A INPUT -p tcp -s 192.168.1.105 -j DROP
#
# iptables -L -v -n  
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 ACCEPT     tcp  --  *      *       192.168.1.105        0.0.0.0/0            quota: 1024000 bytes
    0     0 DROP       tcp  --  *      *       192.168.1.105        0.0.0.0/0     

在主机192.168.1.105上使用ssh访问192.168.1.111,如下,在报文量达到1024k之后,将匹配下一条DROP策略,连接断开。

# iptables -L -v -n
Chain INPUT (policy ACCEPT 717 packets, 115K bytes)
 pkts bytes target     prot opt in     out     source               destination         
19491 1024K ACCEPT     tcp  --  *      *       192.168.1.105        0.0.0.0/0            quota: 1024000 bytes
  105  5772 DROP       tcp  --  *      *       192.168.1.105        0.0.0.0/0   

quota匹配

函数xt_register_matche注册匹配结构quota_mt_reg。

static struct xt_match quota_mt_reg __read_mostly = {
    .name       = "quota",
    .revision   = 0,
    .family     = NFPROTO_UNSPEC,
    .match      = quota_mt,
    .checkentry = quota_mt_check,
    .destroy    = quota_mt_destroy,
    .matchsize  = sizeof(struct xt_quota_info),
    .usersize   = offsetof(struct xt_quota_info, master),
    .me         = THIS_MODULE,
};
static int __init quota_mt_init(void)
{
    return xt_register_match(&quota_mt_reg);

在配置检查函数中,分配xt_quota_priv结构,初始化其中的自旋锁和保存quota值。

static int quota_mt_check(const struct xt_mtchk_param *par)
{
    struct xt_quota_info *q = par->matchinfo;

    if (q->flags & ~XT_QUOTA_MASK)
        return -EINVAL;

    q->master = kmalloc(sizeof(*q->master), GFP_KERNEL);
    if (q->master == NULL)
        return -ENOMEM;

    spin_lock_init(&q->master->lock);
    q->master->quota = q->quota;

匹配函数quota_mt如下,如果quota值大于报文长度,将quota减去报文长度;否则,当小于报文长度时,quota设置为零。

static bool
quota_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct xt_quota_info *q = (void *)par->matchinfo;
    struct xt_quota_priv *priv = q->master;
    bool ret = q->flags & XT_QUOTA_INVERT;

    spin_lock_bh(&priv->lock);
    if (priv->quota >= skb->len) {
        priv->quota -= skb->len;
        ret = !ret;
    } else {
        /* we do not allow even small packets from now on */
        priv->quota = 0;
    }
    spin_unlock_bh(&priv->lock);
    return ret;

内核版本 5.10