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

coordinator/internal/storage/sqlite/sqlite.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"os"
 	"time"
 
 	_ "modernc.org/sqlite"
@@ -37,9 +38,29 @@ func Open(path string) (*sql.DB, error) {
 		_ = db.Close()
 		return nil, fmt.Errorf("ping sqlite database: %w", err)
 	}
+	if err := lockDownDatabase(path); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("lock down sqlite database: %w", err)
+	}
 	return db, nil
 }
 
+// lockDownDatabase restricts the database files to the owner: sqlite creates
+// them with the process umask (0644), which would let any local user read job
+// metadata and password hashes. WAL/SHM siblings inherit the main file's mode,
+// so existing ones are corrected too. Best-effort: failures only warn callers
+// via the returned error, never corrupt state.
+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
+}
+
 // querier is satisfied by both *sql.DB and *sql.Tx, letting every repository
 // method run identically inside or outside a transaction.
 type querier interface {

coordinator/internal/storage/sqlite/sqlite_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"errors"
+	"os"
 	"path/filepath"
 	"testing"
 	"time"
@@ -347,3 +348,19 @@ func TestCancelByJobInvalidatesTasks(t *testing.T) {
 		t.Errorf("cancelled task = %+v", got)
 	}
 }
+
+func TestOpenRestrictsDatabasePermissions(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "locked.db")
+	db, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = db.Close()
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if perm := info.Mode().Perm(); perm != 0o600 {
+		t.Errorf("db perms = %o, want 600", perm)
+	}
+}