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|
package app
import (
"context"
"errors"
"log"
"os"
"os/exec"
"os/signal"
"syscall"
"time"
"hakurei.app/container"
"hakurei.app/container/seccomp"
"hakurei.app/internal"
"hakurei.app/internal/hlog"
)
/*
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <signal.h>
static pid_t hakurei_shim_param_ppid = -1;
// this cannot unblock hlog since Go code is not async-signal-safe
static void hakurei_shim_sigaction(int sig, siginfo_t *si, void *ucontext) {
if (sig != SIGCONT || si == NULL) {
// unreachable
fprintf(stderr, "sigaction: sa_sigaction got invalid siginfo\n");
return;
}
// monitor requests shim exit
if (si->si_pid == hakurei_shim_param_ppid)
exit(254);
fprintf(stderr, "sigaction: got SIGCONT from process %d\n", si->si_pid);
// shim orphaned before monitor delivers a signal
if (getppid() != hakurei_shim_param_ppid)
exit(3);
}
void hakurei_shim_setup_cont_signal(pid_t ppid) {
struct sigaction new_action = {0}, old_action = {0};
if (sigaction(SIGCONT, NULL, &old_action) != 0)
return;
if (old_action.sa_handler != SIG_DFL) {
errno = ENOTRECOVERABLE;
return;
}
new_action.sa_sigaction = hakurei_shim_sigaction;
if (sigemptyset(&new_action.sa_mask) != 0)
return;
new_action.sa_flags = SA_ONSTACK | SA_SIGINFO;
if (sigaction(SIGCONT, &new_action, NULL) != 0)
return;
errno = 0;
hakurei_shim_param_ppid = ppid;
}
*/
import "C"
const shimEnv = "HAKUREI_SHIM"
type shimParams struct {
// monitor pid, checked against ppid in signal handler
Monitor int
// finalised container params
Container *container.Params
// path to outer home directory
Home string
// verbosity pass through
Verbose bool
}
// 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
// the Go runtime does not expose siginfo_t so SIGCONT is handled in C to check si_pid
if _, err = C.hakurei_shim_setup_cont_signal(C.pid_t(params.Monitor)); err != nil {
log.Fatalf("cannot install SIGCONT handler: %v", err)
}
// 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)
}
}
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)
defer stop() // unreachable
z := container.New(ctx, name)
z.Params = *params.Container
z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr
z.Cancel = func(cmd *exec.Cmd) error { return cmd.Process.Signal(os.Interrupt) }
z.WaitDelay = 2 * time.Second
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())
}
}
|
