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package app
import (
"context"
"errors"
"io"
"log"
"os"
"os/exec"
"os/signal"
"runtime"
"sync/atomic"
"syscall"
"time"
"hakurei.app/container"
"hakurei.app/container/seccomp"
"hakurei.app/internal"
"hakurei.app/internal/hlog"
)
//#include "shim-signal.h"
import "C"
const shimEnv = "HAKUREI_SHIM"
type shimParams struct {
// monitor pid, checked against ppid in signal handler
Monitor int
// duration to wait for after interrupting a container's initial process before the container is killed;
// zero value defaults to [DefaultShimWaitDelay], values exceeding [MaxShimWaitDelay] becomes [MaxShimWaitDelay]
WaitDelay time.Duration
// finalised container params
Container *container.Params
// path to outer home directory
Home string
// verbosity pass through
Verbose bool
}
const (
// ShimExitRequest is returned when the monitor process requests shim exit.
ShimExitRequest = 254
// ShimExitOrphan is returned when the shim is orphaned before monitor delivers a signal.
ShimExitOrphan = 3
DefaultShimWaitDelay = 5 * time.Second
MaxShimWaitDelay = 30 * time.Second
)
// ShimMain is the main function of the shim process and runs as the unconstrained target user.
func ShimMain() {
hlog.Prepare("shim")
if err := container.SetDumpable(container.SUID_DUMP_DISABLE); err != nil {
log.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
}
var (
params shimParams
closeSetup func() error
)
if f, err := container.Receive(shimEnv, ¶ms, nil); err != nil {
if errors.Is(err, container.ErrInvalid) {
log.Fatal("invalid config descriptor")
}
if errors.Is(err, container.ErrNotSet) {
log.Fatal("HAKUREI_SHIM not set")
}
log.Fatalf("cannot receive shim setup params: %v", err)
} else {
internal.InstallOutput(params.Verbose)
closeSetup = f
}
var signalPipe io.ReadCloser
// the Go runtime does not expose siginfo_t so SIGCONT is handled in C to check si_pid
if r, w, err := os.Pipe(); err != nil {
log.Fatalf("cannot pipe: %v", err)
} else if _, err = C.hakurei_shim_setup_cont_signal(C.pid_t(params.Monitor), C.int(w.Fd())); err != nil {
log.Fatalf("cannot install SIGCONT handler: %v", err)
} else {
defer runtime.KeepAlive(w)
signalPipe = r
}
// pdeath_signal delivery is checked as if the dying process called kill(2), see kernel/exit.c
if _, _, errno := syscall.Syscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGCONT), 0); errno != 0 {
log.Fatalf("cannot set parent-death signal: %v", errno)
}
// signal handler outcome
var cancelContainer atomic.Pointer[context.CancelFunc]
go func() {
buf := make([]byte, 1)
for {
if _, err := signalPipe.Read(buf); err != nil {
log.Fatalf("cannot read from signal pipe: %v", err)
}
switch buf[0] {
case 0: // got SIGCONT from monitor: shim exit requested
if fp := cancelContainer.Load(); params.Container.ForwardCancel && fp != nil && *fp != nil {
(*fp)()
// shim now bound by ShimWaitDelay, implemented below
continue
}
// setup has not completed, terminate immediately
hlog.Resume()
os.Exit(ShimExitRequest)
return
case 1: // got SIGCONT after adoption: monitor died before delivering signal
hlog.BeforeExit()
os.Exit(ShimExitOrphan)
return
case 2: // unreachable
log.Println("sa_sigaction got invalid siginfo")
case 3: // got SIGCONT from unexpected process: hopefully the terminal driver
log.Println("got SIGCONT from unexpected process")
default: // unreachable
log.Fatalf("got invalid message %d from signal handler", buf[0])
}
}
}()
if params.Container == nil || params.Container.Ops == nil {
log.Fatal("invalid container params")
}
// close setup socket
if err := closeSetup(); err != nil {
log.Printf("cannot close setup pipe: %v", err)
// not fatal
}
// ensure home directory as target user
if s, err := os.Stat(params.Home); err != nil {
if os.IsNotExist(err) {
if err = os.Mkdir(params.Home, 0700); err != nil {
log.Fatalf("cannot create home directory: %v", err)
}
} else {
log.Fatalf("cannot access home directory: %v", err)
}
// home directory is created, proceed
} else if !s.IsDir() {
log.Fatalf("path %q is not a directory", params.Home)
}
var name string
if len(params.Container.Args) > 0 {
name = params.Container.Args[0]
}
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
cancelContainer.Store(&stop)
z := container.New(ctx, name)
z.Params = *params.Container
z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr
z.WaitDelay = params.WaitDelay
if z.WaitDelay == 0 {
z.WaitDelay = DefaultShimWaitDelay
}
if z.WaitDelay > MaxShimWaitDelay {
z.WaitDelay = MaxShimWaitDelay
}
if err := z.Start(); err != nil {
hlog.PrintBaseError(err, "cannot start container:")
os.Exit(1)
}
if err := z.Serve(); err != nil {
hlog.PrintBaseError(err, "cannot configure container:")
}
if err := seccomp.Load(
seccomp.Preset(seccomp.PresetStrict, seccomp.AllowMultiarch),
seccomp.AllowMultiarch,
); err != nil {
log.Fatalf("cannot load syscall filter: %v", err)
}
if err := z.Wait(); err != nil {
var exitError *exec.ExitError
if !errors.As(err, &exitError) {
if errors.Is(err, context.Canceled) {
os.Exit(2)
}
log.Printf("wait: %v", err)
os.Exit(127)
}
os.Exit(exitError.ExitCode())
}
}
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