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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/comp"
"hakurei.app/container/seccomp"
"hakurei.app/hst"
"hakurei.app/message"
)
//#include "shim-signal.h"
import "C"
// shimEnv is the name of the environment variable storing decimal representation of
// setup pipe fd for [container.Receive].
const shimEnv = "HAKUREI_SHIM"
// shimParams is embedded in outcomeState and transmitted from priv side to shim.
type shimParams struct {
// Priv side pid, checked against ppid in signal handler for the syscall.SIGCONT hack.
PrivPID int
// Duration to wait for after the initial process receives os.Interrupt before the container is killed.
// Limits are enforced on the priv side.
WaitDelay time.Duration
// Verbosity pass through from [message.Msg].
Verbose bool
// Outcome setup ops, contains setup state. Populated by outcome.finalise.
Ops []outcomeOp
}
// valid checks shimParams to be safe for use.
func (p *shimParams) valid() bool { return p != nil && p.PrivPID > 0 }
// ShimMain is the main function of the shim process and runs as the unconstrained target user.
func ShimMain() {
log.SetPrefix("shim: ")
log.SetFlags(0)
msg := message.NewMsg(log.Default())
if err := container.SetDumpable(container.SUID_DUMP_DISABLE); err != nil {
log.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
}
var (
state outcomeState
closeSetup func() error
)
if f, err := container.Receive(shimEnv, &state, nil); err != nil {
if errors.Is(err, syscall.EBADF) {
log.Fatal("invalid config descriptor")
}
if errors.Is(err, container.ErrReceiveEnv) {
log.Fatal(shimEnv + " not set")
}
log.Fatalf("cannot receive shim setup params: %v", err)
} else {
msg.SwapVerbose(state.Shim.Verbose)
closeSetup = f
if err = state.populateLocal(direct{}, msg); err != nil {
if m, ok := message.GetMessage(err); ok {
log.Fatal(m)
} else {
log.Fatalf("cannot populate local state: %v", err)
}
}
}
// the Go runtime does not expose siginfo_t so SIGCONT is handled in C to check si_pid
var signalPipe io.ReadCloser
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(state.Shim.PrivPID), 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)
}
stateParams := state.newParams()
for _, op := range state.Shim.Ops {
if err := op.toContainer(stateParams); err != nil {
if m, ok := message.GetMessage(err); ok {
log.Fatal(m)
} else {
log.Fatalf("cannot create container state: %v", err)
}
}
}
// shim exit outcomes
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(); stateParams.params.ForwardCancel && fp != nil && *fp != nil {
(*fp)()
// shim now bound by ShimWaitDelay, implemented below
continue
}
// setup has not completed, terminate immediately
msg.Resume()
os.Exit(hst.ExitRequest)
return
case 1: // got SIGCONT after adoption: monitor died before delivering signal
msg.BeforeExit()
os.Exit(hst.ExitOrphan)
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 stateParams.params.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
}
ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
cancelContainer.Store(&stop)
z := container.New(ctx, msg)
z.Params = *stateParams.params
z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr
// bounds and default enforced in finalise.go
z.WaitDelay = state.Shim.WaitDelay
if err := z.Start(); err != nil {
printMessageError("cannot start container:", err)
os.Exit(hst.ExitFailure)
}
if err := z.Serve(); err != nil {
printMessageError("cannot configure container:", err)
}
if err := seccomp.Load(
seccomp.Preset(comp.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(hst.ExitCancel)
}
log.Printf("wait: %v", err)
os.Exit(127)
}
os.Exit(exitError.ExitCode())
}
}
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