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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build linux
package syscall
import (
"unsafe"
)
// SysProcIDMap holds Container ID to Host ID mappings used for User Namespaces in Linux.
// See user_namespaces(7).
type SysProcIDMap struct {
ContainerID int // Container ID.
HostID int // Host ID.
Size int // Size.
}
type SysProcAttr struct {
Chroot string // Chroot.
Credential *Credential // Credential.
Ptrace bool // Enable tracing.
Setsid bool // Create session.
Setpgid bool // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
Setctty bool // Set controlling terminal to fd Ctty (only meaningful if Setsid is set)
Noctty bool // Detach fd 0 from controlling terminal
Ctty int // Controlling TTY fd
Foreground bool // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
Pgid int // Child's process group ID if Setpgid.
Pdeathsig Signal // Signal that the process will get when its parent dies (Linux only)
Cloneflags uintptr // Flags for clone calls (Linux only)
UidMappings []SysProcIDMap // User ID mappings for user namespaces.
GidMappings []SysProcIDMap // Group ID mappings for user namespaces.
}
// Implemented in runtime package.
func runtime_BeforeFork()
func runtime_AfterFork()
// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
// If a dup or exec fails, write the errno error to pipe.
// (Pipe is close-on-exec so if exec succeeds, it will be closed.)
// In the child, this function must not acquire any locks, because
// they might have been locked at the time of the fork. This means
// no rescheduling, no malloc calls, and no new stack segments.
// For the same reason compiler does not race instrument it.
// The calls to RawSyscall are okay because they are assembly
// functions that do not grow the stack.
func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
// Declare all variables at top in case any
// declarations require heap allocation (e.g., err1).
var (
r1 uintptr
err1 Errno
err2 Errno
nextfd int
i int
p [2]int
)
// Record parent PID so child can test if it has died.
ppid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
// Guard against side effects of shuffling fds below.
// Make sure that nextfd is beyond any currently open files so
// that we can't run the risk of overwriting any of them.
fd := make([]int, len(attr.Files))
nextfd = len(attr.Files)
for i, ufd := range attr.Files {
if nextfd < int(ufd) {
nextfd = int(ufd)
}
fd[i] = int(ufd)
}
nextfd++
// Allocate another pipe for parent to child communication for
// synchronizing writing of User ID/Group ID mappings.
if sys.UidMappings != nil || sys.GidMappings != nil {
if err := forkExecPipe(p[:]); err != nil {
return 0, err.(Errno)
}
}
// About to call fork.
// No more allocation or calls of non-assembly functions.
runtime_BeforeFork()
r1, _, err1 = RawSyscall6(SYS_CLONE, uintptr(SIGCHLD)|sys.Cloneflags, 0, 0, 0, 0, 0)
if err1 != 0 {
runtime_AfterFork()
return 0, err1
}
if r1 != 0 {
// parent; return PID
runtime_AfterFork()
pid = int(r1)
if sys.UidMappings != nil || sys.GidMappings != nil {
Close(p[0])
err := writeUidGidMappings(pid, sys)
if err != nil {
err2 = err.(Errno)
}
RawSyscall(SYS_WRITE, uintptr(p[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2))
Close(p[1])
}
return pid, 0
}
// Fork succeeded, now in child.
// Wait for User ID/Group ID mappings to be written.
if sys.UidMappings != nil || sys.GidMappings != nil {
if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(p[1]), 0, 0); err1 != 0 {
goto childerror
}
r1, _, err1 = RawSyscall(SYS_READ, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2))
if err1 != 0 {
goto childerror
}
if r1 != unsafe.Sizeof(err2) {
err1 = EINVAL
goto childerror
}
if err2 != 0 {
err1 = err2
goto childerror
}
}
// Parent death signal
if sys.Pdeathsig != 0 {
_, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 0, 0, 0)
if err1 != 0 {
goto childerror
}
// Signal self if parent is already dead. This might cause a
// duplicate signal in rare cases, but it won't matter when
// using SIGKILL.
r1, _, _ = RawSyscall(SYS_GETPPID, 0, 0, 0)
if r1 != ppid {
pid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
_, _, err1 := RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0)
if err1 != 0 {
goto childerror
}
}
}
// Enable tracing if requested.
if sys.Ptrace {
_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
if err1 != 0 {
goto childerror
}
}
// Session ID
if sys.Setsid {
_, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
// Set process group
if sys.Setpgid || sys.Foreground {
// Place child in process group.
_, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0)
if err1 != 0 {
goto childerror
}
}
if sys.Foreground {
pgrp := sys.Pgid
if pgrp == 0 {
r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
if err1 != 0 {
goto childerror
}
pgrp = int(r1)
}
// Place process group in foreground.
_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
if err1 != 0 {
goto childerror
}
}
// Chroot
if chroot != nil {
_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)
if err1 != 0 {
goto childerror
}
}
// User and groups
if cred := sys.Credential; cred != nil {
ngroups := uintptr(len(cred.Groups))
var groups unsafe.Pointer
if ngroups > 0 {
groups = unsafe.Pointer(&cred.Groups[0])
}
_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, uintptr(groups), 0)
if err1 != 0 {
goto childerror
}
_, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
if err1 != 0 {
goto childerror
}
_, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
if err1 != 0 {
goto childerror
}
}
// Chdir
if dir != nil {
_, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
if err1 != 0 {
goto childerror
}
}
// Pass 1: look for fd[i] < i and move those up above len(fd)
// so that pass 2 won't stomp on an fd it needs later.
if pipe < nextfd {
_, _, err1 = RawSyscall(_SYS_dup, uintptr(pipe), uintptr(nextfd), 0)
if err1 != 0 {
goto childerror
}
RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
pipe = nextfd
nextfd++
}
for i = 0; i < len(fd); i++ {
if fd[i] >= 0 && fd[i] < int(i) {
_, _, err1 = RawSyscall(_SYS_dup, uintptr(fd[i]), uintptr(nextfd), 0)
if err1 != 0 {
goto childerror
}
RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
fd[i] = nextfd
nextfd++
if nextfd == pipe { // don't stomp on pipe
nextfd++
}
}
}
// Pass 2: dup fd[i] down onto i.
for i = 0; i < len(fd); i++ {
if fd[i] == -1 {
RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
continue
}
if fd[i] == int(i) {
// dup2(i, i) won't clear close-on-exec flag on Linux,
// probably not elsewhere either.
_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_SETFD, 0)
if err1 != 0 {
goto childerror
}
continue
}
// The new fd is created NOT close-on-exec,
// which is exactly what we want.
_, _, err1 = RawSyscall(_SYS_dup, uintptr(fd[i]), uintptr(i), 0)
if err1 != 0 {
goto childerror
}
}
// By convention, we don't close-on-exec the fds we are
// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
// Programs that know they inherit fds >= 3 will need
// to set them close-on-exec.
for i = len(fd); i < 3; i++ {
RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
}
// Detach fd 0 from tty
if sys.Noctty {
_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
if err1 != 0 {
goto childerror
}
}
// Set the controlling TTY to Ctty
if sys.Setctty {
_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
if err1 != 0 {
goto childerror
}
}
// Time to exec.
_, _, err1 = RawSyscall(SYS_EXECVE,
uintptr(unsafe.Pointer(argv0)),
uintptr(unsafe.Pointer(&argv[0])),
uintptr(unsafe.Pointer(&envv[0])))
childerror:
// send error code on pipe
RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
for {
RawSyscall(SYS_EXIT, 253, 0, 0)
}
}
// Try to open a pipe with O_CLOEXEC set on both file descriptors.
func forkExecPipe(p []int) (err error) {
err = Pipe2(p, O_CLOEXEC)
// pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
// might not be implemented.
if err == ENOSYS {
if err = Pipe(p); err != nil {
return
}
if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil {
return
}
_, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
}
return
}
// writeIDMappings writes the user namespace User ID or Group ID mappings to the specified path.
func writeIDMappings(path string, idMap []SysProcIDMap) error {
fd, err := Open(path, O_RDWR, 0)
if err != nil {
return err
}
data := ""
for _, im := range idMap {
data = data + itoa(im.ContainerID) + " " + itoa(im.HostID) + " " + itoa(im.Size) + "\n"
}
bytes, err := ByteSliceFromString(data)
if err != nil {
Close(fd)
return err
}
if _, err := Write(fd, bytes); err != nil {
Close(fd)
return err
}
if err := Close(fd); err != nil {
return err
}
return nil
}
// writeUidGidMappings writes User ID and Group ID mappings for user namespaces
// for a process and it is called from the parent process.
func writeUidGidMappings(pid int, sys *SysProcAttr) error {
if sys.UidMappings != nil {
uidf := "/proc/" + itoa(pid) + "/uid_map"
if err := writeIDMappings(uidf, sys.UidMappings); err != nil {
return err
}
}
if sys.GidMappings != nil {
gidf := "/proc/" + itoa(pid) + "/gid_map"
if err := writeIDMappings(gidf, sys.GidMappings); err != nil {
return err
}
}
return nil
}