hakurei/container/syscall.go

package container

import (
	. "syscall"
	"unsafe"

	"hakurei.app/container/std"
)

// Prctl manipulates various aspects of the behavior of the calling thread or process.
func Prctl(op, arg2, arg3 uintptr) error {
	r, _, errno := Syscall(SYS_PRCTL, op, arg2, arg3)
	if r < 0 {
		return errno
	}
	return nil
}

// SetPtracer allows processes to ptrace(2) the calling process.
func SetPtracer(pid uintptr) error { return Prctl(PR_SET_PTRACER, pid, 0) }

// linux/sched/coredump.h
const (
	SUID_DUMP_DISABLE = iota
	SUID_DUMP_USER
)

// SetDumpable sets the "dumpable" attribute of the calling process.
func SetDumpable(dumpable uintptr) error { return Prctl(PR_SET_DUMPABLE, dumpable, 0) }

// SetNoNewPrivs sets the calling thread's no_new_privs attribute.
func SetNoNewPrivs() error { return Prctl(PR_SET_NO_NEW_PRIVS, 1, 0) }

// Isatty tests whether a file descriptor refers to a terminal.
func Isatty(fd int) bool {
	var buf [8]byte
	r, _, _ := Syscall(
		SYS_IOCTL,
		uintptr(fd),
		TIOCGWINSZ,
		uintptr(unsafe.Pointer(&buf[0])),
	)
	return r == 0
}

// include/uapi/linux/sched.h
const (
	SCHED_NORMAL = iota
	SCHED_FIFO
	SCHED_RR
	SCHED_BATCH
	_ // SCHED_ISO: reserved but not implemented yet
	SCHED_IDLE
	SCHED_DEADLINE
	SCHED_EXT
)

// schedParam is equivalent to struct sched_param from include/linux/sched.h.
type schedParam struct {
	// sched_priority
	priority std.ScmpInt
}

// schedSetscheduler sets both the scheduling policy and parameters for the
// thread whose ID is specified in tid. If tid equals zero, the scheduling
// policy and parameters of the calling thread will be set.
//
// This function is unexported because it is [very subtle to use correctly]. The
// function signature in libc is misleading: pid actually refers to a thread ID.
// The glibc wrapper for this system call ignores this semantic and exposes
// this counterintuitive behaviour.
//
// This function is only called from the container setup thread. Do not reuse
// this if you do not have something similar in place!
//
// [very subtle to use correctly]: https://www.openwall.com/lists/musl/2016/03/01/4
func schedSetscheduler(tid, policy int, param *schedParam) error {
	if r, _, errno := Syscall(
		SYS_SCHED_SETSCHEDULER,
		uintptr(tid),
		uintptr(policy),
		uintptr(unsafe.Pointer(param)),
	); r < 0 {
		return errno
	}
	return nil
}

// IgnoringEINTR makes a function call and repeats it if it returns an
// EINTR error. This appears to be required even though we install all
// signal handlers with SA_RESTART: see #22838, #38033, #38836, #40846.
// Also #20400 and #36644 are issues in which a signal handler is
// installed without setting SA_RESTART. None of these are the common case,
// but there are enough of them that it seems that we can't avoid
// an EINTR loop.
func IgnoringEINTR(fn func() error) error {
	for {
		err := fn()
		if err != EINTR {
			return err
		}
	}
}