go-sandbox/pkg/forkexec/fork_darwin.go
2022-04-03 02:45:53 -07:00

140 lines
3.3 KiB
Go

package forkexec
import (
"syscall"
"unsafe"
"golang.org/x/sys/unix"
)
// Start will fork, load seccomp and execve and being traced by ptrace
// Return pid and potential error
// The runtime OS thread must be locked before calling this function
// if ptrace is set to true
func (r *Runner) Start() (int, error) {
argv0, argv, env, err := prepareExec(r.Args, r.Env)
if err != nil {
return 0, err
}
// prepare work dir
workdir, err := syscallStringFromString(r.WorkDir)
if err != nil {
return 0, err
}
// prepare sandbox profile
profile, err := syscallStringFromString(r.SandboxProfile)
if err != nil {
return 0, err
}
// ensure the socketpair created did not leak to child
syscall.ForkLock.Lock()
// socketpair p is also used to sync with parent before final execve
// p[0] is used by parent and p[1] is used by child
var p [2]int
if err := forkExecSocketPair(&p); err != nil {
syscall.ForkLock.Unlock()
return 0, err
}
// fork in child
pid, err1 := forkAndExecInChild(r, argv0, argv, env, workdir, profile, p)
// restore all signals
afterFork()
syscall.ForkLock.Unlock()
return syncWithChild(r, p, int(pid), err1)
}
func forkExecSocketPair(p *[2]int) error {
var err error
*p, err = syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM, 0)
if err != nil {
return err
}
_, err = fcntl(p[0], syscall.F_SETFD, syscall.FD_CLOEXEC)
if err != nil {
return err
}
_, err = fcntl(p[1], syscall.F_SETFD, syscall.FD_CLOEXEC)
if err != nil {
return err
}
return nil
}
func syncWithChild(r *Runner, p [2]int, pid int, err1 syscall.Errno) (int, error) {
var (
r1 uintptr
err2 syscall.Errno
err error
)
// sync with child
unix.Close(p[1])
// clone syscall failed
if err1 != 0 {
unix.Close(p[0])
return 0, syscall.Errno(err1)
}
r1, _, err1 = syscall3(libc_read_trampoline_addr, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
// child returned error code
if r1 != unsafe.Sizeof(err2) || err2 != 0 || err1 != 0 {
err = handlePipeError(r1, err2)
goto fail
}
// if syncfunc return error, then fail child immediately
if r.SyncFunc != nil {
if err = r.SyncFunc(int(pid)); err != nil {
goto fail
}
}
// otherwise, ack child (err1 == 0)
r1, _, err1 = syscall3(libc_write_trampoline_addr, uintptr(p[0]), uintptr(unsafe.Pointer(&err1)), uintptr(unsafe.Sizeof(err1)))
if err1 != 0 {
goto fail
}
// if read anything mean child failed after sync (close_on_exec so it should not block)
r1, _, err1 = syscall3(libc_read_trampoline_addr, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
unix.Close(p[0])
if r1 != 0 || err1 != 0 {
err = handlePipeError(r1, err2)
goto failAfterClose
}
return int(pid), nil
fail:
unix.Close(p[0])
failAfterClose:
handleChildFailed(int(pid))
return 0, err
}
// check pipe error
func handlePipeError(r1 uintptr, errno syscall.Errno) error {
if r1 == unsafe.Sizeof(errno) {
return syscall.Errno(errno)
}
return syscall.EPIPE
}
func handleChildFailed(pid int) {
var wstatus syscall.WaitStatus
// make sure not blocked
syscall.Kill(pid, syscall.SIGKILL)
// child failed; wait for it to exit, to make sure the zombies don't accumulate
_, err := syscall.Wait4(pid, &wstatus, 0, nil)
for err == syscall.EINTR {
_, err = syscall.Wait4(pid, &wstatus, 0, nil)
}
}