chore(context): always trust xff headers from unix socket (#3359)

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

context.go

@@ -978,14 +978,27 @@ func (c *Context) ClientIP() string {
 		}
 	}
 
-	// It also checks if the remoteIP is a trusted proxy or not.
-	// In order to perform this validation, it will see if the IP is contained within at least one of the CIDR blocks
-	// defined by Engine.SetTrustedProxies()
-	remoteIP := net.ParseIP(c.RemoteIP())
-	if remoteIP == nil {
-		return ""
+	var (
+		trusted  bool
+		remoteIP net.IP
+	)
+	// If gin is listening a unix socket, always trust it.
+	localAddr, ok := c.Request.Context().Value(http.LocalAddrContextKey).(net.Addr)
+	if ok && strings.HasPrefix(localAddr.Network(), "unix") {
+		trusted = true
+	}
+
+	// Fallback
+	if !trusted {
+		// It also checks if the remoteIP is a trusted proxy or not.
+		// In order to perform this validation, it will see if the IP is contained within at least one of the CIDR blocks
+		// defined by Engine.SetTrustedProxies()
+		remoteIP = net.ParseIP(c.RemoteIP())
+		if remoteIP == nil {
+			return ""
+		}
+		trusted = c.engine.isTrustedProxy(remoteIP)
 	}
-	trusted := c.engine.isTrustedProxy(remoteIP)
 
 	if trusted && c.engine.ForwardedByClientIP && c.engine.RemoteIPHeaders != nil {
 		for _, headerName := range c.engine.RemoteIPHeaders {

context_test.go

@@ -1915,6 +1915,16 @@ func TestContextClientIP(t *testing.T) {
 	c.engine.trustedCIDRs, _ = c.engine.prepareTrustedCIDRs()
 	resetContextForClientIPTests(c)
 
+	// unix address
+	addr := &net.UnixAddr{Net: "unix", Name: "@"}
+	c.Request = c.Request.WithContext(context.WithValue(c.Request.Context(), http.LocalAddrContextKey, addr))
+	c.Request.RemoteAddr = addr.String()
+	assert.Equal(t, "20.20.20.20", c.ClientIP())
+
+	// reset
+	c.Request = c.Request.WithContext(context.Background())
+	resetContextForClientIPTests(c)
+
 	// Legacy tests (validating that the defaults don't break the
 	// (insecure!) old behaviour)
 	assert.Equal(t, "20.20.20.20", c.ClientIP())