diff --git a/libcontainer/nsinit/init.go b/libcontainer/nsinit/init.go index ceea294..dc98316 100644 --- a/libcontainer/nsinit/init.go +++ b/libcontainer/nsinit/init.go @@ -185,15 +185,33 @@ func setupRoute(container *libcontainer.Container) error { // and working dir, and closes any leaky file descriptors // before execing the command inside the namespace func FinalizeNamespace(container *libcontainer.Container) error { - if err := capabilities.DropCapabilities(container); err != nil { - return fmt.Errorf("drop capabilities %s", err) - } if err := system.CloseFdsFrom(3); err != nil { return fmt.Errorf("close open file descriptors %s", err) } + + // drop capabilities in bounding set before changing user + if err := capabilities.DropBoundingSet(container); err != nil { + return fmt.Errorf("drop bounding set %s", err) + } + + // preserve existing capabilities while we change users + if err := system.SetKeepCaps(); err != nil { + return fmt.Errorf("set keep caps %s", err) + } + if err := SetupUser(container.User); err != nil { return fmt.Errorf("setup user %s", err) } + + if err := system.ClearKeepCaps(); err != nil { + return fmt.Errorf("clear keep caps %s", err) + } + + // drop all other capabilities + if err := capabilities.DropCapabilities(container); err != nil { + return fmt.Errorf("drop capabilities %s", err) + } + if container.WorkingDir != "" { if err := system.Chdir(container.WorkingDir); err != nil { return fmt.Errorf("chdir to %s %s", container.WorkingDir, err) diff --git a/libcontainer/security/capabilities/capabilities.go b/libcontainer/security/capabilities/capabilities.go index ba72070..64ea961 100644 --- a/libcontainer/security/capabilities/capabilities.go +++ b/libcontainer/security/capabilities/capabilities.go @@ -9,6 +9,25 @@ import ( const allCapabilityTypes = capability.CAPS | capability.BOUNDS +// DropBoundingSet drops the capability bounding set to those specified in the +// container configuration. +func DropBoundingSet(container *libcontainer.Container) error { + c, err := capability.NewPid(os.Getpid()) + if err != nil { + return err + } + + keep := getEnabledCapabilities(container) + c.Clear(capability.BOUNDS) + c.Set(capability.BOUNDS, keep...) + + if err := c.Apply(capability.BOUNDS); err != nil { + return err + } + + return nil +} + // DropCapabilities drops all capabilities for the current process expect those specified in the container configuration. func DropCapabilities(container *libcontainer.Container) error { c, err := capability.NewPid(os.Getpid()) diff --git a/system/calls_linux.go b/system/calls_linux.go index faead01..6986051 100644 --- a/system/calls_linux.go +++ b/system/calls_linux.go @@ -135,6 +135,22 @@ func GetParentDeathSignal() (int, error) { return sig, nil } +func SetKeepCaps() error { + if _, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_KEEPCAPS, 1, 0); err != 0 { + return err + } + + return nil +} + +func ClearKeepCaps() error { + if _, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_KEEPCAPS, 0, 0); err != 0 { + return err + } + + return nil +} + func Setctty() error { if _, _, err := syscall.RawSyscall(syscall.SYS_IOCTL, 0, uintptr(syscall.TIOCSCTTY), 0); err != 0 { return err