lib/httpserver: revert 9b7e532172

Reason for revert: this commit doesn't resolve real security issues,
while it complicates the resulting code in subtle ways (aka security circus).

Comparison of two strings (passwords, auth keys) takes a few nanoseconds.
This comparison is performed in non-trivial http handler, which takes thousands
of nanoseconds, and the request handler timing is non-deterministic because of Go runtime,
Go GC and other concurrently executed goroutines. The request handler timing is even
more non-deterministic when the application is executed in shared environments
such as Kubernetes, where many other applications may run on the same host and use
shared resources of this host (CPU, RAM bandwidth, network bandwidth).

Additionally, it is expected that the passwords and auth keys are passed via TLS-encrypted connections.
Establishing TLS connections takes additional non-trivial time (millions of nanoseconds),
which depends on many factors such as network latency, network congestion, etc.

This makes impossible to conduct timing attack on passwords and auth keys in VictoriaMetrics components.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6423/files
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6392

docs/CHANGELOG.md

@@ -37,7 +37,6 @@ Released at 2024-06-24
 
 **Update note 2: `*.passwordFile` and similar flags are no longer trimming trailing whitespaces at the end of content. Make sure to update the templating of password files or HTTP endpoints to not include trailing whitespaces before the upgrade. See [this](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6503) PR for the details.**
 
-* FEATURE: all VictoriaMetrics components: use constant-time comparison for comparing HTTP basic auth credentials and auth keys. This should prevent timing attacks when comparing these credentials. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6392) for details. Thanks to @wasim-nihal for [the pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6423).
 * FEATURE: [alerts-vmagent](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/deployment/docker/alerts-vmagent.yml): add new alerting rules `StreamAggrFlushTimeout` and `StreamAggrDedupFlushTimeout` to notify about issues during stream aggregation.
 * FEATURE: [dashboards/vmagent](https://grafana.com/grafana/dashboards/12683): add row `Streaming aggregation` with panels related to [streaming aggregation](https://docs.victoriametrics.com/stream-aggregation/) process.
 * FEATURE: [vmauth](https://docs.victoriametrics.com/vmauth/): add `idleConnTimeout` flag set to 50s by default. It should reduce the probability of `broken pipe` or `connection reset by peer` errors in vmauth logs.

lib/httpserver/httpserver.go

@@ -2,7 +2,6 @@ package httpserver
 
 import (
 	"context"
-	"crypto/subtle"
 	"crypto/tls"
 	_ "embed"
 	"errors"
@@ -443,7 +442,7 @@ func CheckAuthFlag(w http.ResponseWriter, r *http.Request, flagValue string, fla
 	if flagValue == "" {
 		return CheckBasicAuth(w, r)
 	}
-	if !constantTimeEqual(r.FormValue("authKey"), flagValue) {
+	if r.FormValue("authKey") != flagValue {
 		authKeyRequestErrors.Inc()
 		http.Error(w, fmt.Sprintf("The provided authKey doesn't match -%s", flagName), http.StatusUnauthorized)
 		return false
@@ -460,7 +459,7 @@ func CheckBasicAuth(w http.ResponseWriter, r *http.Request) bool {
 	}
 	username, password, ok := r.BasicAuth()
 	if ok {
-		if constantTimeEqual(username, *httpAuthUsername) && constantTimeEqual(password, httpAuthPassword.Get()) {
+		if username == *httpAuthUsername && password == httpAuthPassword.Get() {
 			return true
 		}
 		authBasicRequestErrors.Inc()
@@ -713,16 +712,3 @@ func LogError(req *http.Request, errStr string) {
 	remoteAddr := GetQuotedRemoteAddr(req)
 	logger.Errorf("uri: %s, remote address: %q: %s", uri, remoteAddr, errStr)
 }
-
-// constantTimeEqual compares two strings in constant-time.
-//
-// It returns true if they are equal, else it returns false.
-func constantTimeEqual(s1, s2 string) bool {
-	a := []byte(s1)
-	b := []byte(s2)
-	// check length explicitly because ConstantTimeCompare doesn't spend time on comparing length
-	if subtle.ConstantTimeEq(int32(len(a)), int32(len(b))) == 0 {
-		return false
-	}
-	return subtle.ConstantTimeCompare(a, b) == 1
-}