278 lines
9.7 KiB
Go
278 lines
9.7 KiB
Go
// SPDX-License-Identifier: MIT
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// SPDX-FileCopyrightText: © 2015 LabStack LLC and Echo contributors
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package echo
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import (
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"net"
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"net/http"
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"strings"
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)
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/**
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By: https://github.com/tmshn (See: https://github.com/labstack/echo/pull/1478 , https://github.com/labstack/echox/pull/134 )
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Source: https://echo.labstack.com/guide/ip-address/
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IP address plays fundamental role in HTTP; it's used for access control, auditing, geo-based access analysis and more.
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Echo provides handy method [`Context#RealIP()`](https://godoc.org/github.com/labstack/echo#Context) for that.
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However, it is not trivial to retrieve the _real_ IP address from requests especially when you put L7 proxies before the application.
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In such situation, _real_ IP needs to be relayed on HTTP layer from proxies to your app, but you must not trust HTTP headers unconditionally.
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Otherwise, you might give someone a chance of deceiving you. **A security risk!**
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To retrieve IP address reliably/securely, you must let your application be aware of the entire architecture of your infrastructure.
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In Echo, this can be done by configuring `Echo#IPExtractor` appropriately.
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This guides show you why and how.
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> Note: if you dont' set `Echo#IPExtractor` explicitly, Echo fallback to legacy behavior, which is not a good choice.
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Let's start from two questions to know the right direction:
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1. Do you put any HTTP (L7) proxy in front of the application?
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- It includes both cloud solutions (such as AWS ALB or GCP HTTP LB) and OSS ones (such as Nginx, Envoy or Istio ingress gateway).
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2. If yes, what HTTP header do your proxies use to pass client IP to the application?
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## Case 1. With no proxy
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If you put no proxy (e.g.: directory facing to the internet), all you need to (and have to) see is IP address from network layer.
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Any HTTP header is untrustable because the clients have full control what headers to be set.
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In this case, use `echo.ExtractIPDirect()`.
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```go
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e.IPExtractor = echo.ExtractIPDirect()
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```
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## Case 2. With proxies using `X-Forwarded-For` header
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[`X-Forwared-For` (XFF)](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-For) is the popular header
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to relay clients' IP addresses.
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At each hop on the proxies, they append the request IP address at the end of the header.
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Following example diagram illustrates this behavior.
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```text
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┌──────────┐ ┌──────────┐ ┌──────────┐ ┌──────────┐
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│ "Origin" │───────────>│ Proxy 1 │───────────>│ Proxy 2 │───────────>│ Your app │
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│ (IP: a) │ │ (IP: b) │ │ (IP: c) │ │ │
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└──────────┘ └──────────┘ └──────────┘ └──────────┘
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Case 1.
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XFF: "" "a" "a, b"
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~~~~~~
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Case 2.
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XFF: "x" "x, a" "x, a, b"
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~~~~~~~~~
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↑ What your app will see
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```
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In this case, use **first _untrustable_ IP reading from right**. Never use first one reading from left, as it is
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configurable by client. Here "trustable" means "you are sure the IP address belongs to your infrastructure".
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In above example, if `b` and `c` are trustable, the IP address of the client is `a` for both cases, never be `x`.
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In Echo, use `ExtractIPFromXFFHeader(...TrustOption)`.
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```go
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e.IPExtractor = echo.ExtractIPFromXFFHeader()
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```
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By default, it trusts internal IP addresses (loopback, link-local unicast, private-use and unique local address
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from [RFC6890](https://tools.ietf.org/html/rfc6890), [RFC4291](https://tools.ietf.org/html/rfc4291) and
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[RFC4193](https://tools.ietf.org/html/rfc4193)).
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To control this behavior, use [`TrustOption`](https://godoc.org/github.com/labstack/echo#TrustOption)s.
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E.g.:
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```go
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e.IPExtractor = echo.ExtractIPFromXFFHeader(
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TrustLinkLocal(false),
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TrustIPRanges(lbIPRange),
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)
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```
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- Ref: https://godoc.org/github.com/labstack/echo#TrustOption
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## Case 3. With proxies using `X-Real-IP` header
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`X-Real-IP` is another HTTP header to relay clients' IP addresses, but it carries only one address unlike XFF.
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If your proxies set this header, use `ExtractIPFromRealIPHeader(...TrustOption)`.
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```go
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e.IPExtractor = echo.ExtractIPFromRealIPHeader()
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```
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Again, it trusts internal IP addresses by default (loopback, link-local unicast, private-use and unique local address
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from [RFC6890](https://tools.ietf.org/html/rfc6890), [RFC4291](https://tools.ietf.org/html/rfc4291) and
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[RFC4193](https://tools.ietf.org/html/rfc4193)).
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To control this behavior, use [`TrustOption`](https://godoc.org/github.com/labstack/echo#TrustOption)s.
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- Ref: https://godoc.org/github.com/labstack/echo#TrustOption
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> **Never forget** to configure the outermost proxy (i.e.; at the edge of your infrastructure) **not to pass through incoming headers**.
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> Otherwise there is a chance of fraud, as it is what clients can control.
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## About default behavior
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In default behavior, Echo sees all of first XFF header, X-Real-IP header and IP from network layer.
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As you might already notice, after reading this article, this is not good.
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Sole reason this is default is just backward compatibility.
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## Private IP ranges
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See: https://en.wikipedia.org/wiki/Private_network
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Private IPv4 address ranges (RFC 1918):
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* 10.0.0.0 – 10.255.255.255 (24-bit block)
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* 172.16.0.0 – 172.31.255.255 (20-bit block)
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* 192.168.0.0 – 192.168.255.255 (16-bit block)
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Private IPv6 address ranges:
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* fc00::/7 address block = RFC 4193 Unique Local Addresses (ULA)
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*/
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type ipChecker struct {
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trustLoopback bool
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trustLinkLocal bool
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trustPrivateNet bool
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trustExtraRanges []*net.IPNet
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}
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// TrustOption is config for which IP address to trust
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type TrustOption func(*ipChecker)
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// TrustLoopback configures if you trust loopback address (default: true).
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func TrustLoopback(v bool) TrustOption {
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return func(c *ipChecker) {
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c.trustLoopback = v
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}
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}
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// TrustLinkLocal configures if you trust link-local address (default: true).
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func TrustLinkLocal(v bool) TrustOption {
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return func(c *ipChecker) {
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c.trustLinkLocal = v
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}
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}
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// TrustPrivateNet configures if you trust private network address (default: true).
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func TrustPrivateNet(v bool) TrustOption {
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return func(c *ipChecker) {
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c.trustPrivateNet = v
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}
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}
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// TrustIPRange add trustable IP ranges using CIDR notation.
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func TrustIPRange(ipRange *net.IPNet) TrustOption {
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return func(c *ipChecker) {
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c.trustExtraRanges = append(c.trustExtraRanges, ipRange)
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}
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}
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func newIPChecker(configs []TrustOption) *ipChecker {
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checker := &ipChecker{trustLoopback: true, trustLinkLocal: true, trustPrivateNet: true}
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for _, configure := range configs {
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configure(checker)
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}
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return checker
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}
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// Go1.16+ added `ip.IsPrivate()` but until that use this implementation
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func isPrivateIPRange(ip net.IP) bool {
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if ip4 := ip.To4(); ip4 != nil {
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return ip4[0] == 10 ||
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ip4[0] == 172 && ip4[1]&0xf0 == 16 ||
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ip4[0] == 192 && ip4[1] == 168
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}
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return len(ip) == net.IPv6len && ip[0]&0xfe == 0xfc
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}
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func (c *ipChecker) trust(ip net.IP) bool {
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if c.trustLoopback && ip.IsLoopback() {
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return true
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}
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if c.trustLinkLocal && ip.IsLinkLocalUnicast() {
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return true
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}
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if c.trustPrivateNet && isPrivateIPRange(ip) {
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return true
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}
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for _, trustedRange := range c.trustExtraRanges {
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if trustedRange.Contains(ip) {
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return true
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}
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}
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return false
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}
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// IPExtractor is a function to extract IP addr from http.Request.
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// Set appropriate one to Echo#IPExtractor.
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// See https://echo.labstack.com/guide/ip-address for more details.
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type IPExtractor func(*http.Request) string
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// ExtractIPDirect extracts IP address using actual IP address.
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// Use this if your server faces to internet directory (i.e.: uses no proxy).
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func ExtractIPDirect() IPExtractor {
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return extractIP
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}
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func extractIP(req *http.Request) string {
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ra, _, _ := net.SplitHostPort(req.RemoteAddr)
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return ra
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}
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// ExtractIPFromRealIPHeader extracts IP address using x-real-ip header.
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// Use this if you put proxy which uses this header.
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func ExtractIPFromRealIPHeader(options ...TrustOption) IPExtractor {
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checker := newIPChecker(options)
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return func(req *http.Request) string {
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directIP := extractIP(req)
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realIP := req.Header.Get(HeaderXRealIP)
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if realIP == "" {
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return directIP
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}
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if checker.trust(net.ParseIP(directIP)) {
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realIP = strings.TrimPrefix(realIP, "[")
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realIP = strings.TrimSuffix(realIP, "]")
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if rIP := net.ParseIP(realIP); rIP != nil {
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return realIP
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}
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}
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return directIP
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}
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}
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// ExtractIPFromXFFHeader extracts IP address using x-forwarded-for header.
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// Use this if you put proxy which uses this header.
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// This returns nearest untrustable IP. If all IPs are trustable, returns furthest one (i.e.: XFF[0]).
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func ExtractIPFromXFFHeader(options ...TrustOption) IPExtractor {
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checker := newIPChecker(options)
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return func(req *http.Request) string {
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directIP := extractIP(req)
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xffs := req.Header[HeaderXForwardedFor]
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if len(xffs) == 0 {
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return directIP
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}
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ips := append(strings.Split(strings.Join(xffs, ","), ","), directIP)
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for i := len(ips) - 1; i >= 0; i-- {
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ips[i] = strings.TrimSpace(ips[i])
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ips[i] = strings.TrimPrefix(ips[i], "[")
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ips[i] = strings.TrimSuffix(ips[i], "]")
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ip := net.ParseIP(ips[i])
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if ip == nil {
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// Unable to parse IP; cannot trust entire records
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return directIP
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}
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if !checker.trust(ip) {
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return ip.String()
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}
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}
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// All of the IPs are trusted; return first element because it is furthest from server (best effort strategy).
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return strings.TrimSpace(ips[0])
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}
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}
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