blob: 0da6c9649668819193798af3c692458f25858bbd [file] [log] [blame]
// 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"
)
//sysnb raw_prctl(option int, arg2 int, arg3 int, arg4 int, arg5 int) (ret int, err Errno)
//prctl(option _C_int, arg2 _C_long, arg3 _C_long, arg4 _C_long, arg5 _C_long) _C_int
//sysnb rawUnshare(flags int) (err Errno)
//unshare(flags _C_int) _C_int
//sysnb rawMount(source *byte, target *byte, fstype *byte, flags uintptr, data *byte) (err Errno)
//mount(source *byte, target *byte, fstype *byte, flags _C_long, data *byte) _C_int
//sysnb rawOpenat(dirfd int, pathname *byte, flags int, perm uint32) (fd int, err Errno)
//__go_openat(dirfd _C_int, pathname *byte, flags _C_int, perm Mode_t) _C_int
// 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 tells the child to call ptrace(PTRACE_TRACEME).
// Call runtime.LockOSThread before starting a process with this set,
// and don't call UnlockOSThread until done with PtraceSyscall calls.
Ptrace bool
Setsid bool // Create session.
// Setpgid sets the process group ID of the child to Pgid,
// or, if Pgid == 0, to the new child's process ID.
Setpgid bool
// Setctty sets the controlling terminal of the child to
// file descriptor Ctty. Ctty must be a descriptor number
// in the child process: an index into ProcAttr.Files.
// This is only meaningful if Setsid is true.
Setctty bool
Noctty bool // Detach fd 0 from controlling terminal
Ctty int // Controlling TTY fd
// Foreground places the child process group in the foreground.
// This implies Setpgid. The Ctty field must be set to
// the descriptor of the controlling TTY.
// Unlike Setctty, in this case Ctty must be a descriptor
// number in the parent process.
Foreground bool
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)
Unshareflags uintptr // Flags for unshare calls (Linux only)
UidMappings []SysProcIDMap // User ID mappings for user namespaces.
GidMappings []SysProcIDMap // Group ID mappings for user namespaces.
// GidMappingsEnableSetgroups enabling setgroups syscall.
// If false, then setgroups syscall will be disabled for the child process.
// This parameter is no-op if GidMappings == nil. Otherwise for unprivileged
// users this should be set to false for mappings work.
GidMappingsEnableSetgroups bool
AmbientCaps []uintptr // Ambient capabilities (Linux only)
}
var (
none = [...]byte{'n', 'o', 'n', 'e', 0}
slash = [...]byte{'/', 0}
)
// Implemented in runtime package.
func runtime_BeforeFork()
func runtime_AfterFork()
func runtime_AfterForkInChild()
// Implemented in clone_linux.c
//go:noescape
func rawClone(flags _C_ulong, child_stack *byte, ptid *Pid_t, ctid *Pid_t, regs unsafe.Pointer) _C_long
// 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.
//go:norace
func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
// Set up and fork. This returns immediately in the parent or
// if there's an error.
r1, err1, p, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe)
if locked {
runtime_AfterFork()
}
if err1 != 0 {
return 0, err1
}
// parent; return PID
pid = int(r1)
if sys.UidMappings != nil || sys.GidMappings != nil {
Close(p[0])
var err2 Errno
// uid/gid mappings will be written after fork and unshare(2) for user
// namespaces.
if sys.Unshareflags&CLONE_NEWUSER == 0 {
if err := writeUidGidMappings(pid, sys); err != nil {
err2 = err.(Errno)
}
}
raw_write(p[1], (*byte)(unsafe.Pointer(&err2)), int(unsafe.Sizeof(err2)))
Close(p[1])
}
return pid, 0
}
const _LINUX_CAPABILITY_VERSION_3 = 0x20080522
type capHeader struct {
version uint32
pid int32
}
type capData struct {
effective uint32
permitted uint32
inheritable uint32
}
type caps struct {
hdr capHeader
data [2]capData
}
// See CAP_TO_INDEX in linux/capability.h:
func capToIndex(cap uintptr) uintptr { return cap >> 5 }
// See CAP_TO_MASK in linux/capability.h:
func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) }
// forkAndExecInChild1 implements the body of forkAndExecInChild up to
// the parent's post-fork path. This is a separate function so we can
// separate the child's and parent's stack frames if we're using
// vfork.
//
// This is go:noinline because the point is to keep the stack frames
// of this and forkAndExecInChild separate.
//
//go:noinline
//go:norace
func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (r1 uintptr, err1 Errno, p [2]int, locked bool) {
// Defined in linux/prctl.h starting with Linux 4.3.
const (
PR_CAP_AMBIENT = 0x2f
PR_CAP_AMBIENT_RAISE = 0x2
)
// vfork requires that the child not touch any of the parent's
// active stack frames. Hence, the child does all post-fork
// processing in this stack frame and never returns, while the
// parent returns immediately from this frame and does all
// post-fork processing in the outer frame.
// Declare all variables at top in case any
// declarations require heap allocation (e.g., err1).
var (
err2 Errno
nextfd int
i int
r2 int
caps caps
fd1 int
puid, psetgroups, pgid []byte
uidmap, setgroups, gidmap []byte
)
if sys.UidMappings != nil {
puid = []byte("/proc/self/uid_map\000")
uidmap = formatIDMappings(sys.UidMappings)
}
if sys.GidMappings != nil {
psetgroups = []byte("/proc/self/setgroups\000")
pgid = []byte("/proc/self/gid_map\000")
if sys.GidMappingsEnableSetgroups {
setgroups = []byte("allow\000")
} else {
setgroups = []byte("deny\000")
}
gidmap = formatIDMappings(sys.GidMappings)
}
// Record parent PID so child can test if it has died.
ppid := raw_getpid()
// 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 {
err1 = err.(Errno)
return
}
}
// About to call fork.
// No more allocation or calls of non-assembly functions.
runtime_BeforeFork()
locked = true
r2 = int(rawClone(_C_ulong(uintptr(SIGCHLD)|sys.Cloneflags), nil, nil, nil, unsafe.Pointer(nil)))
if r2 < 0 {
err1 = GetErrno()
}
if r2 != 0 {
// If we're in the parent, we must return immediately
// so we're not in the same stack frame as the child.
// This can at most use the return PC, which the child
// will not modify, and the results of
// rawVforkSyscall, which must have been written after
// the child was replaced.
r1 = uintptr(r2)
return
}
// Fork succeeded, now in child.
runtime_AfterForkInChild()
// Enable the "keep capabilities" flag to set ambient capabilities later.
if len(sys.AmbientCaps) > 0 {
_, err1 = raw_prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
// Wait for User ID/Group ID mappings to be written.
if sys.UidMappings != nil || sys.GidMappings != nil {
if err1 = raw_close(p[1]); err1 != 0 {
goto childerror
}
r2, err1 = raw_read(p[0], (*byte)(unsafe.Pointer(&err2)), int(unsafe.Sizeof(err2)))
if err1 != 0 {
goto childerror
}
if r2 != int(unsafe.Sizeof(err2)) {
err1 = EINVAL
goto childerror
}
if err2 != 0 {
err1 = err2
goto childerror
}
}
// Session ID
if sys.Setsid {
err1 = raw_setsid()
if err1 != 0 {
goto childerror
}
}
// Set process group
if sys.Setpgid || sys.Foreground {
// Place child in process group.
err1 = raw_setpgid(0, sys.Pgid)
if err1 != 0 {
goto childerror
}
}
if sys.Foreground {
pgrp := Pid_t(sys.Pgid)
if pgrp == 0 {
pgrp = raw_getpid()
}
// Place process group in foreground.
_, err1 = raw_ioctl_ptr(sys.Ctty, TIOCSPGRP, unsafe.Pointer(&pgrp))
if err1 != 0 {
goto childerror
}
}
// Unshare
if sys.Unshareflags != 0 {
err1 = rawUnshare(int(sys.Unshareflags))
if err1 != 0 {
goto childerror
}
if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.GidMappings != nil {
dirfd := int(_AT_FDCWD)
if fd1, err1 = rawOpenat(dirfd, &psetgroups[0], O_WRONLY, 0); err1 != 0 {
goto childerror
}
_, err1 = raw_write(fd1, &setgroups[0], len(setgroups))
if err1 != 0 {
goto childerror
}
if err1 = raw_close(fd1); err1 != 0 {
goto childerror
}
if fd1, err1 = rawOpenat(dirfd, &pgid[0], O_WRONLY, 0); err1 != 0 {
goto childerror
}
_, err1 = raw_write(fd1, &gidmap[0], len(gidmap))
if err1 != 0 {
goto childerror
}
if err1 = raw_close(fd1); err1 != 0 {
goto childerror
}
}
if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.UidMappings != nil {
dirfd := int(_AT_FDCWD)
if fd1, err1 = rawOpenat(dirfd, &puid[0], O_WRONLY, 0); err1 != 0 {
goto childerror
}
_, err1 = raw_write(fd1, &uidmap[0], len(uidmap))
if err1 != 0 {
goto childerror
}
if err1 = raw_close(fd1); err1 != 0 {
goto childerror
}
}
// The unshare system call in Linux doesn't unshare mount points
// mounted with --shared. Systemd mounts / with --shared. For a
// long discussion of the pros and cons of this see debian bug 739593.
// The Go model of unsharing is more like Plan 9, where you ask
// to unshare and the namespaces are unconditionally unshared.
// To make this model work we must further mark / as MS_PRIVATE.
// This is what the standard unshare command does.
if sys.Unshareflags&CLONE_NEWNS == CLONE_NEWNS {
err1 = rawMount(&none[0], &slash[0], nil, MS_REC|MS_PRIVATE, nil)
if err1 != 0 {
goto childerror
}
}
}
// Chroot
if chroot != nil {
err1 = raw_chroot(chroot)
if err1 != 0 {
goto childerror
}
}
// User and groups
if cred := sys.Credential; cred != nil {
ngroups := len(cred.Groups)
var groups unsafe.Pointer
if ngroups > 0 {
groups = unsafe.Pointer(&cred.Groups[0])
}
if !(sys.GidMappings != nil && !sys.GidMappingsEnableSetgroups && ngroups == 0) && !cred.NoSetGroups {
err1 = raw_setgroups(ngroups, groups)
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
}
}
if len(sys.AmbientCaps) != 0 {
// Ambient capabilities were added in the 4.3 kernel,
// so it is safe to always use _LINUX_CAPABILITY_VERSION_3.
caps.hdr.version = _LINUX_CAPABILITY_VERSION_3
if _, _, err1 = RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
goto childerror
}
for _, c := range sys.AmbientCaps {
// Add the c capability to the permitted and inheritable capability mask,
// otherwise we will not be able to add it to the ambient capability mask.
caps.data[capToIndex(c)].permitted |= capToMask(c)
caps.data[capToIndex(c)].inheritable |= capToMask(c)
}
if _, _, err1 = RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
goto childerror
}
for _, c := range sys.AmbientCaps {
_, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
}
// Chdir
if dir != nil {
err1 = raw_chdir(dir)
if err1 != 0 {
goto childerror
}
}
// Parent death signal
if sys.Pdeathsig != 0 {
_, err1 = raw_prctl(PR_SET_PDEATHSIG, int(sys.Pdeathsig), 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 := raw_getppid()
if r1 != ppid {
pid := raw_getpid()
err1 = raw_kill(pid, sys.Pdeathsig)
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 = raw_dup3(pipe, nextfd, O_CLOEXEC)
if err1 == ENOSYS {
err1 = raw_dup2(pipe, nextfd)
if err1 != 0 {
goto childerror
}
raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
} else if err1 != 0 {
goto childerror
}
pipe = nextfd
nextfd++
}
for i = 0; i < len(fd); i++ {
if fd[i] >= 0 && fd[i] < int(i) {
if nextfd == pipe { // don't stomp on pipe
nextfd++
}
err1 = raw_dup3(fd[i], nextfd, O_CLOEXEC)
if err1 == ENOSYS {
err1 = raw_dup2(fd[i], nextfd)
if err1 != 0 {
goto childerror
}
raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
} else if err1 != 0 {
goto childerror
}
fd[i] = nextfd
nextfd++
}
}
// Pass 2: dup fd[i] down onto i.
for i = 0; i < len(fd); i++ {
if fd[i] == -1 {
raw_close(i)
continue
}
if fd[i] == int(i) {
// dup2(i, i) won't clear close-on-exec flag on Linux,
// probably not elsewhere either.
_, err1 = raw_fcntl(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 = raw_dup2(fd[i], i)
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++ {
raw_close(i)
}
// Detach fd 0 from tty
if sys.Noctty {
_, err1 = raw_ioctl(0, TIOCNOTTY, 0)
if err1 != 0 {
goto childerror
}
}
// Set the controlling TTY to Ctty
if sys.Setctty {
_, err1 = raw_ioctl(sys.Ctty, TIOCSCTTY, 1)
if err1 != 0 {
goto childerror
}
}
// Enable tracing if requested.
// Do this right before exec so that we don't unnecessarily trace the runtime
// setting up after the fork. See issue #21428.
if sys.Ptrace {
err1 = raw_ptrace(_PTRACE_TRACEME, 0, 0, 0)
if err1 != 0 {
goto childerror
}
}
// Time to exec.
err1 = raw_execve(argv0, &argv[0], &envv[0])
childerror:
// send error code on pipe
raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
for {
raw_exit(253)
}
}
// 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
}
func formatIDMappings(idMap []SysProcIDMap) []byte {
var data []byte
for _, im := range idMap {
data = append(data, []byte(itoa(im.ContainerID)+" "+itoa(im.HostID)+" "+itoa(im.Size)+"\n")...)
}
return data
}
// 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
}
if _, err := Write(fd, formatIDMappings(idMap)); err != nil {
Close(fd)
return err
}
if err := Close(fd); err != nil {
return err
}
return nil
}
// writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false
// and "allow" if enable is true.
// This is needed since kernel 3.19, because you can't write gid_map without
// disabling setgroups() system call.
func writeSetgroups(pid int, enable bool) error {
sgf := "/proc/" + itoa(pid) + "/setgroups"
fd, err := Open(sgf, O_RDWR, 0)
if err != nil {
return err
}
var data []byte
if enable {
data = []byte("allow")
} else {
data = []byte("deny")
}
if _, err := Write(fd, data); err != nil {
Close(fd)
return err
}
return Close(fd)
}
// 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 {
// If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK.
if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT {
return err
}
gidf := "/proc/" + itoa(pid) + "/gid_map"
if err := writeIDMappings(gidf, sys.GidMappings); err != nil {
return err
}
}
return nil
}