libgo: update to Go1.10beta1

[official-gcc.git] / libgo / go / syscall / exec_linux.go

// 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

// 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)
        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
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])
                err := writeUidGidMappings(pid, sys)
                var err2 Errno
                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
}

// 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
        )

        // 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 = RawSyscall6(SYS_PRCTL, PR_SET_KEEPCAPS, 1, 0, 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 = 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
                }
        }

        // 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
                }
                // 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
                }
        }

        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_dup2(pipe, nextfd)
                if err1 != 0 {
                        goto childerror
                }
                raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
                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_dup2(fd[i], nextfd)
                        if err1 != 0 {
                                goto childerror
                        }
                        raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
                        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, sys.Ctty)
                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, nil, nil)
                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
}

// 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
}

// 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
}