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firewall.go
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firewall.go
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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package middleware
import (
"context"
"net"
"net/http"
"strings"
"github.com/google/exposure-notifications-verification-server/pkg/controller"
"github.com/google/exposure-notifications-verification-server/pkg/render"
"github.com/google/exposure-notifications-server/pkg/logging"
"github.com/gorilla/mux"
)
// ProcessFirewall verifies the application-level firewall configuration.
//
// This must come after the realm has been loaded in the context, probably via a
// different middleware.
func ProcessFirewall(ctx context.Context, h *render.Renderer, typ string) mux.MiddlewareFunc {
logger := logging.FromContext(ctx).Named("middleware.ProcessFirewall")
return func(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
realm := controller.RealmFromContext(ctx)
if realm == nil {
controller.MissingRealm(w, r, h)
return
}
var allowedCIDRs []string
switch typ {
case "adminapi":
allowedCIDRs = realm.AllowedCIDRsAdminAPI
case "apiserver":
allowedCIDRs = realm.AllowedCIDRsAPIServer
case "server":
allowedCIDRs = realm.AllowedCIDRsServer
default:
logger.Errorw("unknown firewall type", "type", typ)
}
// If there's no CIDRs, all traffic is allowed.
if len(allowedCIDRs) == 0 {
next.ServeHTTP(w, r)
return
}
logger.Debugw("validating ip in cidr block", "type", typ)
// Get the remote address.
ipStr := r.RemoteAddr
// Check if x-forwarded-for exists, the load balancer sets this, and the
// first entry is the real client IP.
xff := r.Header.Get("x-forwarded-for")
if xff != "" {
ipStr = strings.Split(xff, ",")[0]
}
// Parse as an IP.
ip := net.ParseIP(ipStr)
if ip == nil {
logger.Errorw("provided ip could not be parsed")
}
for _, c := range allowedCIDRs {
_, cidr, err := net.ParseCIDR(c)
if err != nil {
logger.Warnw("failed to parse cidr", "cidr", c, "error", err)
continue
}
if cidr.Contains(ip) {
next.ServeHTTP(w, r)
return
}
}
logger.Errorw("ip is not in an allowed cidr block")
controller.Unauthorized(w, r, h)
})
}
}