src/pkg/syscall/exec_linux.go - go - Git at Google

 // 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"
 )

 type SysProcAttr struct {
 	Chroot     string      // Chroot.
 	Credential *Credential // Credential.
 	Ptrace     bool        // Enable tracing.
 	Setsid     bool        // Create session.
 	Setpgid    bool        // Set process group ID to new pid (SYSV setpgrp)
 	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 (Linux only)
 	Pdeathsig  Signal      // Signal that the process will get when its parent dies (Linux only)
 	Cloneflags uintptr     // Flags for clone calls (Linux only)
 }

 // 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
 		nextfd int
 		i      int
 	)

 	// 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++

 	// 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()
 		return int(r1), 0
 	}

 	// Fork succeeded, now in child.

 	// 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 == 1 {
 			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 {
 		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
 		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_DUP2, 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_DUP2, 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_DUP2, 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 && sys.Ctty >= 0 {
 		_, _, 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
 }
	// 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"
	)

	type SysProcAttr struct {
	Chroot string // Chroot.
	Credential *Credential // Credential.
	Ptrace bool // Enable tracing.
	Setsid bool // Create session.
	Setpgid bool // Set process group ID to new pid (SYSV setpgrp)
	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 (Linux only)
	Pdeathsig Signal // Signal that the process will get when its parent dies (Linux only)
	Cloneflags uintptr // Flags for clone calls (Linux only)
	}

	// 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
	nextfd int
	i int
	)

	// 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++

	// 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()
	return int(r1), 0
	}

	// Fork succeeded, now in child.

	// 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 == 1 {
	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 {
	_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
	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_DUP2, 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_DUP2, 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_DUP2, 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 && sys.Ctty >= 0 {
	_, _, 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
	}