Thales Maciel
d73efe6fbc
Replace the shell-string launcher in buildProcessRunner with a direct
exec.Command. The previous sh -c wrapper relied on shellQuote escaping
for every MachineConfig field that flowed into the launch script; any
future field that ever carried an attacker-controlled value would have
become RCE-as-root. The new path passes binary path and flags as
separate argv entries, so there is no shell to interpret anything.
The wrapper also did two things the shell can no longer do for us:
1. umask 077 — moved to syscall.Umask in cmd/bangerd/main.go so every
firecracker child (and any other file the daemon creates) inherits
0600 by default. Single-user dev sandbox state should be private.
2. chown_watcher — the SDK's HTTP probe inside Machine.Start connects
to the API socket the moment it appears. Under sudo the socket is
created root-owned and the daemon's connect(2) gets EACCES, so the
post-Start EnsureSocketAccess never runs. The shell papered over
this with a backgrounded chown loop. Replaced by
fcproc.EnsureSocketAccessForAsync: same race-window guarantee, in
pure Go, kicked off in LaunchFirecracker right before Start and
awaited right after.
Tests updated: shell-substring assertions replaced with cmd-arg
assertions, plus a new fcproc test pinning the async chown sequence.
Smoke (full systemd two-service install + KVM scenarios) passes.
365 lines
12 KiB
Go
365 lines
12 KiB
Go
package daemon
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import (
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"context"
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"errors"
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"log/slog"
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"os"
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"strconv"
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"strings"
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"syscall"
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"banger/internal/daemon/dmsnap"
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"banger/internal/daemon/fcproc"
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"banger/internal/firecracker"
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"banger/internal/hostnat"
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"banger/internal/model"
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"banger/internal/paths"
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"banger/internal/roothelper"
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"banger/internal/system"
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)
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type privilegedOps interface {
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EnsureBridge(context.Context) error
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CreateTap(context.Context, string) error
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DeleteTap(context.Context, string) error
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SyncResolverRouting(context.Context, string) error
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ClearResolverRouting(context.Context) error
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EnsureNAT(context.Context, string, string, bool) error
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CreateDMSnapshot(context.Context, string, string, string) (dmSnapshotHandles, error)
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CleanupDMSnapshot(context.Context, dmSnapshotHandles) error
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RemoveDMSnapshot(context.Context, string) error
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FsckSnapshot(context.Context, string) error
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ReadExt4File(context.Context, string, string) ([]byte, error)
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WriteExt4Files(context.Context, string, []roothelper.Ext4Write) error
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ResolveFirecrackerBinary(context.Context, string) (string, error)
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LaunchFirecracker(context.Context, roothelper.FirecrackerLaunchRequest) (int, error)
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EnsureSocketAccess(context.Context, string, string) error
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FindFirecrackerPID(context.Context, string) (int, error)
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KillProcess(context.Context, int) error
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SignalProcess(context.Context, int, string) error
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ProcessRunning(context.Context, int, string) (bool, error)
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}
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type localPrivilegedOps struct {
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runner system.CommandRunner
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logger *slog.Logger
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config model.DaemonConfig
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layout paths.Layout
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clientUID int
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clientGID int
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}
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func (n *HostNetwork) privOps() privilegedOps {
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if n.priv == nil {
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n.priv = newLocalPrivilegedOps(n.runner, n.logger, n.config, n.layout, os.Getuid(), os.Getgid())
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}
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return n.priv
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}
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func (s *VMService) privOps() privilegedOps {
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if s.priv == nil {
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s.priv = newLocalPrivilegedOps(s.runner, s.logger, s.config, s.layout, os.Getuid(), os.Getgid())
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}
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return s.priv
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}
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func newLocalPrivilegedOps(runner system.CommandRunner, logger *slog.Logger, cfg model.DaemonConfig, layout paths.Layout, clientUID, clientGID int) privilegedOps {
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if clientUID < 0 {
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clientUID = os.Getuid()
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}
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if clientGID < 0 {
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clientGID = os.Getgid()
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}
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return &localPrivilegedOps{
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runner: runner,
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logger: logger,
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config: cfg,
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layout: layout,
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clientUID: clientUID,
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clientGID: clientGID,
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}
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}
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func (o *localPrivilegedOps) EnsureBridge(ctx context.Context) error {
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return o.fc().EnsureBridge(ctx)
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}
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func (o *localPrivilegedOps) CreateTap(ctx context.Context, tapName string) error {
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return o.fc().CreateTapOwned(ctx, tapName, o.clientUID, o.clientGID)
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}
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func (o *localPrivilegedOps) DeleteTap(ctx context.Context, tapName string) error {
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_, err := o.runner.RunSudo(ctx, "ip", "link", "del", tapName)
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return err
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}
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func (o *localPrivilegedOps) SyncResolverRouting(ctx context.Context, serverAddr string) error {
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if strings.TrimSpace(o.config.BridgeName) == "" || strings.TrimSpace(serverAddr) == "" {
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return nil
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}
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if _, err := system.LookupExecutable("resolvectl"); err != nil {
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return nil
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}
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if _, err := o.runner.RunSudo(ctx, "resolvectl", "dns", o.config.BridgeName, serverAddr); err != nil {
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return err
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}
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if _, err := o.runner.RunSudo(ctx, "resolvectl", "domain", o.config.BridgeName, vmResolverRouteDomain); err != nil {
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return err
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}
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_, err := o.runner.RunSudo(ctx, "resolvectl", "default-route", o.config.BridgeName, "no")
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return err
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}
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func (o *localPrivilegedOps) ClearResolverRouting(ctx context.Context) error {
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if strings.TrimSpace(o.config.BridgeName) == "" {
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return nil
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}
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if _, err := system.LookupExecutable("resolvectl"); err != nil {
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return nil
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}
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_, err := o.runner.RunSudo(ctx, "resolvectl", "revert", o.config.BridgeName)
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return err
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}
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func (o *localPrivilegedOps) EnsureNAT(ctx context.Context, guestIP, tap string, enable bool) error {
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return hostnat.Ensure(ctx, o.runner, guestIP, tap, enable)
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}
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func (o *localPrivilegedOps) CreateDMSnapshot(ctx context.Context, rootfsPath, cowPath, dmName string) (dmSnapshotHandles, error) {
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return dmsnap.Create(ctx, o.runner, rootfsPath, cowPath, dmName)
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}
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func (o *localPrivilegedOps) CleanupDMSnapshot(ctx context.Context, handles dmSnapshotHandles) error {
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return dmsnap.Cleanup(ctx, o.runner, handles)
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}
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func (o *localPrivilegedOps) RemoveDMSnapshot(ctx context.Context, target string) error {
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return dmsnap.Remove(ctx, o.runner, target)
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}
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func (o *localPrivilegedOps) FsckSnapshot(ctx context.Context, dmDev string) error {
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if _, err := o.runner.RunSudo(ctx, "e2fsck", "-fy", dmDev); err != nil {
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if code := system.ExitCode(err); code < 0 || code > 1 {
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return err
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}
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}
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return nil
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}
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func (o *localPrivilegedOps) ReadExt4File(ctx context.Context, imagePath, guestPath string) ([]byte, error) {
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return system.ReadExt4File(ctx, o.runner, imagePath, guestPath)
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}
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func (o *localPrivilegedOps) WriteExt4Files(ctx context.Context, imagePath string, files []roothelper.Ext4Write) error {
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for _, file := range files {
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mode := os.FileMode(file.Mode)
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if mode == 0 {
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mode = 0o644
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}
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if err := system.WriteExt4FileOwned(ctx, o.runner, imagePath, file.GuestPath, mode, 0, 0, file.Data); err != nil {
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return err
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}
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}
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return nil
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}
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func (o *localPrivilegedOps) ResolveFirecrackerBinary(_ context.Context, requested string) (string, error) {
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manager := fcproc.New(o.runner, fcproc.Config{FirecrackerBin: normalizeFirecrackerBinary(requested, o.config.FirecrackerBin)}, o.logger)
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return manager.ResolveBinary()
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}
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func (o *localPrivilegedOps) LaunchFirecracker(ctx context.Context, req roothelper.FirecrackerLaunchRequest) (int, error) {
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machine, err := firecracker.NewMachine(ctx, firecracker.MachineConfig{
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BinaryPath: req.BinaryPath,
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VMID: req.VMID,
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SocketPath: req.SocketPath,
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LogPath: req.LogPath,
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MetricsPath: req.MetricsPath,
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KernelImagePath: req.KernelImagePath,
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InitrdPath: req.InitrdPath,
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KernelArgs: req.KernelArgs,
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Drives: req.Drives,
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TapDevice: req.TapDevice,
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VSockPath: req.VSockPath,
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VSockCID: req.VSockCID,
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VCPUCount: req.VCPUCount,
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MemoryMiB: req.MemoryMiB,
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Logger: o.logger,
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})
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if err != nil {
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return 0, err
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}
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// Race the chown against the SDK's HTTP probe inside Start: when the
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// daemon is non-root, firecracker is launched under sudo and the API
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// socket appears root-owned. Without a concurrent chown the SDK's
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// connect(2) gets EACCES and Start times out before our post-Start
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// EnsureSocketAccess can ever run.
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chownDone := o.fc().EnsureSocketAccessForAsync(ctx, []string{req.SocketPath, req.VSockPath}, o.clientUID, o.clientGID)
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startErr := machine.Start(ctx)
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chownErr := <-chownDone
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if startErr != nil {
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if pid := o.fc().ResolvePID(context.Background(), machine, req.SocketPath); pid > 0 {
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_ = o.KillProcess(context.Background(), pid)
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}
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return 0, startErr
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}
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if chownErr != nil {
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return 0, chownErr
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}
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if err := o.EnsureSocketAccess(ctx, req.SocketPath, "firecracker api socket"); err != nil {
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return 0, err
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}
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if strings.TrimSpace(req.VSockPath) != "" {
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if err := o.EnsureSocketAccess(ctx, req.VSockPath, "firecracker vsock socket"); err != nil {
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return 0, err
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}
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}
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pid := o.fc().ResolvePID(context.Background(), machine, req.SocketPath)
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if pid <= 0 {
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return 0, errors.New("firecracker started but pid could not be resolved")
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}
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return pid, nil
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}
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func (o *localPrivilegedOps) EnsureSocketAccess(ctx context.Context, socketPath, label string) error {
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return o.fc().EnsureSocketAccessFor(ctx, socketPath, label, o.clientUID, o.clientGID)
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}
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func (o *localPrivilegedOps) FindFirecrackerPID(ctx context.Context, apiSock string) (int, error) {
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return o.fc().FindPID(ctx, apiSock)
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}
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func (o *localPrivilegedOps) KillProcess(ctx context.Context, pid int) error {
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return o.fc().Kill(ctx, pid)
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}
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func (o *localPrivilegedOps) SignalProcess(ctx context.Context, pid int, signal string) error {
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if strings.TrimSpace(signal) == "" {
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signal = "TERM"
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}
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_, err := o.runner.RunSudo(ctx, "kill", "-"+signal, strconv.Itoa(pid))
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return err
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}
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func (o *localPrivilegedOps) ProcessRunning(_ context.Context, pid int, apiSock string) (bool, error) {
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return system.ProcessRunning(pid, apiSock), nil
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}
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func (o *localPrivilegedOps) fc() *fcproc.Manager {
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return fcproc.New(o.runner, fcproc.Config{
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FirecrackerBin: normalizeFirecrackerBinary("", o.config.FirecrackerBin),
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BridgeName: o.config.BridgeName,
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BridgeIP: o.config.BridgeIP,
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CIDR: o.config.CIDR,
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RuntimeDir: o.layout.RuntimeDir,
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}, o.logger)
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}
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type helperPrivilegedOps struct {
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client *roothelper.Client
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config model.DaemonConfig
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layout paths.Layout
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}
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func newHelperPrivilegedOps(client *roothelper.Client, cfg model.DaemonConfig, layout paths.Layout) privilegedOps {
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return &helperPrivilegedOps{client: client, config: cfg, layout: layout}
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}
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func (o *helperPrivilegedOps) EnsureBridge(ctx context.Context) error {
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return o.client.EnsureBridge(ctx, o.networkConfig())
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}
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func (o *helperPrivilegedOps) CreateTap(ctx context.Context, tapName string) error {
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return o.client.CreateTap(ctx, o.networkConfig(), tapName)
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}
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func (o *helperPrivilegedOps) DeleteTap(ctx context.Context, tapName string) error {
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return o.client.DeleteTap(ctx, tapName)
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}
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func (o *helperPrivilegedOps) SyncResolverRouting(ctx context.Context, serverAddr string) error {
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return o.client.SyncResolverRouting(ctx, o.config.BridgeName, serverAddr)
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}
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func (o *helperPrivilegedOps) ClearResolverRouting(ctx context.Context) error {
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return o.client.ClearResolverRouting(ctx, o.config.BridgeName)
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}
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func (o *helperPrivilegedOps) EnsureNAT(ctx context.Context, guestIP, tap string, enable bool) error {
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return o.client.EnsureNAT(ctx, guestIP, tap, enable)
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}
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func (o *helperPrivilegedOps) CreateDMSnapshot(ctx context.Context, rootfsPath, cowPath, dmName string) (dmSnapshotHandles, error) {
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return o.client.CreateDMSnapshot(ctx, rootfsPath, cowPath, dmName)
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}
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func (o *helperPrivilegedOps) CleanupDMSnapshot(ctx context.Context, handles dmSnapshotHandles) error {
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return o.client.CleanupDMSnapshot(ctx, handles)
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}
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func (o *helperPrivilegedOps) RemoveDMSnapshot(ctx context.Context, target string) error {
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return o.client.RemoveDMSnapshot(ctx, target)
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}
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func (o *helperPrivilegedOps) FsckSnapshot(ctx context.Context, dmDev string) error {
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return o.client.FsckSnapshot(ctx, dmDev)
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}
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func (o *helperPrivilegedOps) ReadExt4File(ctx context.Context, imagePath, guestPath string) ([]byte, error) {
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return o.client.ReadExt4File(ctx, imagePath, guestPath)
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}
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func (o *helperPrivilegedOps) WriteExt4Files(ctx context.Context, imagePath string, files []roothelper.Ext4Write) error {
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return o.client.WriteExt4Files(ctx, imagePath, files)
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}
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func (o *helperPrivilegedOps) ResolveFirecrackerBinary(ctx context.Context, requested string) (string, error) {
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return o.client.ResolveFirecrackerBinary(ctx, normalizeFirecrackerBinary(requested, o.config.FirecrackerBin))
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}
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func (o *helperPrivilegedOps) LaunchFirecracker(ctx context.Context, req roothelper.FirecrackerLaunchRequest) (int, error) {
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req.Network = o.networkConfig()
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return o.client.LaunchFirecracker(ctx, req)
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}
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func (o *helperPrivilegedOps) EnsureSocketAccess(ctx context.Context, socketPath, label string) error {
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if info, err := os.Stat(socketPath); err == nil {
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if stat, ok := info.Sys().(*syscall.Stat_t); ok && int(stat.Uid) == os.Getuid() {
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return os.Chmod(socketPath, 0o600)
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}
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}
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return o.client.EnsureSocketAccess(ctx, socketPath, label)
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}
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func (o *helperPrivilegedOps) FindFirecrackerPID(ctx context.Context, apiSock string) (int, error) {
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return o.client.FindFirecrackerPID(ctx, apiSock)
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}
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func (o *helperPrivilegedOps) KillProcess(ctx context.Context, pid int) error {
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return o.client.KillProcess(ctx, pid)
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}
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func (o *helperPrivilegedOps) SignalProcess(ctx context.Context, pid int, signal string) error {
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return o.client.SignalProcess(ctx, pid, signal)
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}
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func (o *helperPrivilegedOps) ProcessRunning(ctx context.Context, pid int, apiSock string) (bool, error) {
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return o.client.ProcessRunning(ctx, pid, apiSock)
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}
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func (o *helperPrivilegedOps) networkConfig() roothelper.NetworkConfig {
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return roothelper.NetworkConfig{
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BridgeName: o.config.BridgeName,
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BridgeIP: o.config.BridgeIP,
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CIDR: o.config.CIDR,
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}
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}
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func normalizeFirecrackerBinary(requested, configured string) string {
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requested = strings.TrimSpace(requested)
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if requested != "" {
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return requested
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}
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return strings.TrimSpace(configured)
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}
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