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- // Copyright (c) 2016-2017 Daniel Oaks <daniel@danieloaks.net>
- // released under the MIT license
-
- package connection_limits
-
- import (
- "errors"
- "fmt"
- "net"
- "sync"
- )
-
- // LimiterConfig controls the automated connection limits.
- type LimiterConfig struct {
- Enabled bool
- CidrLenIPv4 int `yaml:"cidr-len-ipv4"`
- CidrLenIPv6 int `yaml:"cidr-len-ipv6"`
- IPsPerCidr int `yaml:"ips-per-subnet"`
- Exempted []string
- }
-
- var (
- errTooManyClients = errors.New("Too many clients in subnet")
- )
-
- // Limiter manages the automated client connection limits.
- type Limiter struct {
- sync.Mutex
-
- enabled bool
- ipv4Mask net.IPMask
- ipv6Mask net.IPMask
- // subnetLimit is the maximum number of clients per subnet
- subnetLimit int
- // population holds IP -> count of clients connected from there
- population map[string]int
-
- // exemptedIPs holds IPs that are exempt from limits
- exemptedIPs map[string]bool
- // exemptedNets holds networks that are exempt from limits
- exemptedNets []net.IPNet
- }
-
- // maskAddr masks the given IPv4/6 address with our cidr limit masks.
- func (cl *Limiter) maskAddr(addr net.IP) net.IP {
- if addr.To4() == nil {
- // IPv6 addr
- addr = addr.Mask(cl.ipv6Mask)
- } else {
- // IPv4 addr
- addr = addr.Mask(cl.ipv4Mask)
- }
-
- return addr
- }
-
- // AddClient adds a client to our population if possible. If we can't, throws an error instead.
- // 'force' is used to add already-existing clients (i.e. ones that are already on the network).
- func (cl *Limiter) AddClient(addr net.IP, force bool) error {
- cl.Lock()
- defer cl.Unlock()
-
- if !cl.enabled {
- return nil
- }
-
- // check exempted lists
- // we don't track populations for exempted addresses or nets - this is by design
- if cl.exemptedIPs[addr.String()] {
- return nil
- }
- for _, ex := range cl.exemptedNets {
- if ex.Contains(addr) {
- return nil
- }
- }
-
- // check population
- cl.maskAddr(addr)
- addrString := addr.String()
-
- if cl.population[addrString]+1 > cl.subnetLimit && !force {
- return errTooManyClients
- }
-
- cl.population[addrString] = cl.population[addrString] + 1
-
- return nil
- }
-
- // RemoveClient removes the given address from our population
- func (cl *Limiter) RemoveClient(addr net.IP) {
- cl.Lock()
- defer cl.Unlock()
-
- if !cl.enabled {
- return
- }
-
- addrString := addr.String()
- cl.population[addrString] = cl.population[addrString] - 1
-
- // safety limiter
- if cl.population[addrString] < 0 {
- cl.population[addrString] = 0
- }
- }
-
- // NewLimiter returns a new connection limit handler.
- // The handler is functional, but disabled; it can be enabled via `ApplyConfig`.
- func NewLimiter() *Limiter {
- var cl Limiter
-
- // initialize empty population; all other state is configurable
- cl.population = make(map[string]int)
-
- return &cl
- }
-
- // ApplyConfig atomically applies a config update to a connection limit handler
- func (cl *Limiter) ApplyConfig(config LimiterConfig) error {
- // assemble exempted nets
- exemptedIPs := make(map[string]bool)
- var exemptedNets []net.IPNet
- for _, cidr := range config.Exempted {
- ipaddr := net.ParseIP(cidr)
- _, netaddr, err := net.ParseCIDR(cidr)
-
- if ipaddr == nil && err != nil {
- return fmt.Errorf("Could not parse exempted IP/network [%s]", cidr)
- }
-
- if ipaddr != nil {
- exemptedIPs[ipaddr.String()] = true
- } else {
- exemptedNets = append(exemptedNets, *netaddr)
- }
- }
-
- cl.Lock()
- defer cl.Unlock()
-
- cl.enabled = config.Enabled
- cl.ipv4Mask = net.CIDRMask(config.CidrLenIPv4, 32)
- cl.ipv6Mask = net.CIDRMask(config.CidrLenIPv6, 128)
- // subnetLimit is explicitly NOT capped at a minimum of one.
- // this is so that CL config can be used to allow ONLY clients from exempted IPs/nets
- cl.subnetLimit = config.IPsPerCidr
- cl.exemptedIPs = exemptedIPs
- cl.exemptedNets = exemptedNets
-
- return nil
- }
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