Harden the surface: 0600 databases, checksum-verified installs, rate-limited login and key exchange

coordinator/internal/userservice/storage/sqlite/sqlite.go

@@ -7,6 +7,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"os"
 	"time"
 
 	_ "modernc.org/sqlite"
@@ -290,6 +291,17 @@ func indexOf(haystack, needle string) int {
 }
 
 // Open opens (and creates when missing) the userservice database file.
+func lockDownDatabase(path string) error {
+	for _, candidate := range []string{path, path + "-wal", path + "-shm"} {
+		if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
+			if err := os.Chmod(candidate, 0o600); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 func Open(path string) (*sql.DB, error) {
 	dsn := fmt.Sprintf("file:%s?_pragma=busy_timeout(10000)&_pragma=journal_mode(WAL)&_pragma=foreign_keys(1)&_pragma=synchronous(NORMAL)", path)
 	db, err := sql.Open("sqlite", dsn)
@@ -300,5 +312,9 @@ func Open(path string) (*sql.DB, error) {
 		_ = db.Close()
 		return nil, fmt.Errorf("ping userservice database: %w", err)
 	}
+	if err := lockDownDatabase(path); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("lock down userservice database: %w", err)
+	}
 	return db, nil
 }

coordinator/internal/userservice/transport/http/ratelimit.go

@@ -0,0 +1,97 @@
+package http
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// The same per-address token-bucket policy as the coordinator transport:
+// login is the credential brute-force surface, the exchange the only public
+// token-minting one.
+const (
+	loginRatePerMinute    = 10
+	loginBurst            = 5
+	exchangeRatePerMinute = 30
+	exchangeBurst         = 10
+)
+
+type tokenBucket struct {
+	mu     sync.Mutex
+	tokens float64
+	last   time.Time
+	rate   float64
+	burst  float64
+}
+
+func newTokenBucket(ratePerMinute, burst float64) *tokenBucket {
+	return &tokenBucket{tokens: burst, last: time.Now(), rate: ratePerMinute / 60, burst: burst}
+}
+
+func (b *tokenBucket) allow() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	now := time.Now()
+	b.tokens += now.Sub(b.last).Seconds() * b.rate
+	if b.tokens > b.burst {
+		b.tokens = b.burst
+	}
+	b.last = now
+	if b.tokens < 1 {
+		return false
+	}
+	b.tokens--
+	return true
+}
+
+type ipLimiter struct {
+	mu            sync.Mutex
+	buckets       map[string]*tokenBucket
+	ratePerMinute float64
+	burst         float64
+}
+
+func newIPLimiter(ratePerMinute, burst float64) *ipLimiter {
+	return &ipLimiter{buckets: map[string]*tokenBucket{}, ratePerMinute: ratePerMinute, burst: burst}
+}
+
+func (l *ipLimiter) Allow(r *http.Request) bool {
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		host = r.RemoteAddr
+	}
+	l.mu.Lock()
+	if len(l.buckets) > 1024 {
+		cutoff := time.Now().Add(-10 * time.Minute)
+		for addr, bucket := range l.buckets {
+			bucket.mu.Lock()
+			idle := bucket.last.Before(cutoff)
+			bucket.mu.Unlock()
+			if idle {
+				delete(l.buckets, addr)
+			}
+		}
+	}
+	bucket, ok := l.buckets[host]
+	if !ok {
+		bucket = newTokenBucket(l.ratePerMinute, l.burst)
+		l.buckets[host] = bucket
+	}
+	l.mu.Unlock()
+	return bucket.allow()
+}
+
+func rateLimited(limiter *ipLimiter, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !limiter.Allow(r) {
+			w.Header().Set("Retry-After", "60")
+			writeJSON(w, http.StatusTooManyRequests, errorResponse{
+				Error:     "too many requests, try again shortly",
+				RequestID: requestIDFrom(r.Context()),
+			})
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}

coordinator/internal/userservice/transport/http/server.go

@@ -51,14 +51,14 @@ func NewServer(log *slog.Logger, uc UseCases, issuer auth.Issuer) http.Handler {
 	// Method-aware patterns (Go 1.22+): a GET to /register is a 405, not a match.
 	mux.HandleFunc("GET /health", h.handleHealth)
 	mux.HandleFunc("POST /register", h.handleRegister)
-	mux.HandleFunc("POST /login", h.handleLogin)
+	mux.Handle("POST /login", rateLimited(newIPLimiter(loginRatePerMinute, loginBurst), http.HandlerFunc(h.handleLogin)))
 	// /me proves a token round-trips; it sits behind JWT auth.
 	mux.Handle("GET /me", chain(http.HandlerFunc(h.handleMe), withJWT(issuer)))
 
 	// Worker keys: a user mints a long-lived key (JWT-protected), and a worker
 	// trades it for a short-lived JWT on the public exchange endpoint — the key
 	// itself is the credential there, so no prior token is required.
-	mux.HandleFunc("POST /worker-tokens/exchange", h.handleExchangeWorkerKey)
+	mux.Handle("POST /worker-tokens/exchange", rateLimited(newIPLimiter(exchangeRatePerMinute, exchangeBurst), http.HandlerFunc(h.handleExchangeWorkerKey)))
 	mux.Handle("POST /worker-keys", chain(http.HandlerFunc(h.handleCreateWorkerKey), withJWT(issuer)))
 	mux.Handle("GET /worker-keys", chain(http.HandlerFunc(h.handleListWorkerKeys), withJWT(issuer)))
 	mux.Handle("DELETE /worker-keys/{id}", chain(http.HandlerFunc(h.handleRevokeWorkerKey), withJWT(issuer)))