webapi: Rate limit for admin login requests.

Only allow 3 requests per second. Return "429 Too Many Requests" when this rate is exceeded.

go.mod

@@ -59,6 +59,7 @@ require (
 	golang.org/x/net v0.6.0 // indirect
 	golang.org/x/sys v0.5.0 // indirect
 	golang.org/x/text v0.7.0 // indirect
+	golang.org/x/time v0.3.0
 	google.golang.org/protobuf v1.28.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )

go.sum

@@ -242,6 +242,8 @@ golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/text v0.7.0 h1:4BRB4x83lYWy72KwLD/qYDuTu7q9PjSagHvijDw7cLo=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/time v0.3.0 h1:rg5rLMjNzMS1RkNLzCG38eapWhnYLFYXDXj2gOlr8j4=
+golang.org/x/time v0.3.0/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=

webapi/admin.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2022 The Decred developers
+// Copyright (c) 2020-2023 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -200,9 +200,9 @@ func (s *Server) adminLogin(c *gin.Context) {
 	if password != s.cfg.AdminPass {
 		s.log.Warnf("Failed login attempt from %s", c.ClientIP())
 		c.HTML(http.StatusUnauthorized, "login.html", gin.H{
-			"WebApiCache":       s.cache.getData(),
-			"WebApiCfg":         s.cfg,
-			"IncorrectPassword": true,
+			"WebApiCache":    s.cache.getData(),
+			"WebApiCfg":      s.cfg,
+			"FailedLoginMsg": "Incorrect password",
 		})
 		return
 	}

webapi/middleware.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2022 The Decred developers
+// Copyright (c) 2020-2023 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -10,6 +10,8 @@ import (
 	"io"
 	"net/http"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/decred/dcrd/blockchain/stake/v4"
 	"github.com/decred/vspd/rpc"
@@ -18,8 +20,43 @@ import (
 	"github.com/gin-gonic/gin/binding"
 	"github.com/gorilla/sessions"
 	"github.com/jrick/wsrpc/v2"
+	"golang.org/x/time/rate"
 )
 
+// rateLimit middleware limits how many requests each client IP can submit per
+// second. If the limit is exceeded the limitExceeded handler will be executed
+// and the context will be aborted.
+func rateLimit(limit rate.Limit, limitExceeded gin.HandlerFunc) gin.HandlerFunc {
+	var limitersMtx sync.Mutex
+	limiters := make(map[string]*rate.Limiter)
+
+	// Clear limiters every hour so they arent accumulating infinitely.
+	go func() {
+		for {
+			<-time.After(time.Hour)
+			limitersMtx.Lock()
+			limiters = make(map[string]*rate.Limiter)
+			limitersMtx.Unlock()
+		}
+	}()
+
+	return func(c *gin.Context) {
+		limitersMtx.Lock()
+		defer limitersMtx.Unlock()
+
+		// Create a limiter for this IP if one does not exist.
+		if _, ok := limiters[c.ClientIP()]; !ok {
+			limiters[c.ClientIP()] = rate.NewLimiter(limit, 1)
+		}
+
+		// Check if this IP exceeds limit.
+		if !limiters[c.ClientIP()].Allow() {
+			limitExceeded(c)
+			c.Abort()
+		}
+	}
+}
+
 // withSession middleware adds a gorilla session to the request context for
 // downstream handlers to make use of. Sessions are used by admin pages to
 // maintain authentication status.

webapi/templates/login.html

@@ -4,9 +4,9 @@
     <h1>Login</h1>
     <form class="py-3" action="/admin" method="post">
 
-        <input type="password" name="password" required placeholder="Enter password">
+        <input type="password" name="password" autofocus required placeholder="Enter password">
         
-        <p class="my-1 orange" style="visibility:{{ if .IncorrectPassword }}visible{{ else }}hidden{{ end }};">Incorrect password</p>
+        <p class="my-1 orange" style="visibility:{{ if .FailedLoginMsg }}visible{{ else }}hidden{{ end }};">{{ .FailedLoginMsg }}</p>
 
         <button class="btn btn-primary" type="submit">Login</button>
     </form>

webapi/webapi.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2022 The Decred developers
+// Copyright (c) 2020-2023 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -249,7 +249,17 @@ func (s *Server) router(cookieSecret []byte, dcrd rpc.DcrdConnect, wallets rpc.W
 	login := router.Group("/admin").Use(
 		s.withSession(cookieStore),
 	)
-	login.POST("", s.adminLogin)
+
+	// Limit login attempts to 3 per second.
+	loginRateLmiter := rateLimit(3, func(c *gin.Context) {
+		s.log.Warnf("Login rate limit exceeded by %s", c.ClientIP())
+		c.HTML(http.StatusTooManyRequests, "login.html", gin.H{
+			"WebApiCache":    s.cache.getData(),
+			"WebApiCfg":      s.cfg,
+			"FailedLoginMsg": "Rate limit exceeded",
+		})
+	})
+	login.POST("", loginRateLmiter, s.adminLogin)
 
 	admin := router.Group("/admin").Use(
 		s.withWalletClients(wallets), s.withSession(cookieStore), s.requireAdmin,