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syscall: separate ProcSysAttr and forkAndExecInChild for FreeBSD 

To allow adding fields to ProcSysAttr which are supported on FreeBSD but
not on other BSDs.

For now exec_freebsd.go is an exact copy of exec_bsd.go with adjusted
build tags and copyright year.

For #46258
For #46259

Change-Id: I7667a0cdf1ca86ef64a147b77c06db70c5f8eb90
Reviewed-on: https://go-review.googlesource.com/c/go/+/355569
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Tobias Klauser 2021-10-13 15:42:31 +02:00 committed by Tobias Klauser
parent 9e4dc6f37f
commit 1349c6eb1e
2 changed files with 265 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/syscall/exec_bsd.go
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@ -2,8 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build dragonfly || freebsd || netbsd || (openbsd && mips64)
// +build dragonfly freebsd netbsd openbsd,mips64
//go:build dragonfly || netbsd || (openbsd && mips64)
// +build dragonfly netbsd openbsd,mips64
package syscall

263
src/syscall/exec_freebsd.go Normal file
View File

@ -0,0 +1,263 @@
// Copyright 2021 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.
package syscall
import (
"unsafe"
)
type SysProcAttr struct {
Chroot string // Chroot.
Credential *Credential // Credential.
Ptrace bool // Enable tracing.
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.
}
// Implemented in runtime package.
func runtime_BeforeFork()
func runtime_AfterFork()
func runtime_AfterForkInChild()
// 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) {
// 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 = RawSyscall(SYS_FORK, 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.
// 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 {
// This should really be pid_t, however _C_int (aka int32) is
// generally equivalent.
pgrp := _C_int(sys.Pgid)
if pgrp == 0 {
r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
if err1 != 0 {
goto childerror
}
pgrp = _C_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
}
}
// Restore the signal mask. We do this after TIOCSPGRP to avoid
// having the kernel send a SIGTTOU signal to the process group.
runtime_AfterForkInChild()
// 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))
groups := uintptr(0)
if ngroups > 0 {
groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
}
if !cred.NoSetGroups {
_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, 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) {
if nextfd == pipe { // don't stomp on pipe
nextfd++
}
_, _, 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++
}
}
// 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 {
_, _, 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)
}
}