syscall: use dup3 in forkAndExecInChild on OpenBSD

Use dup3(oldfd, newfd, O_CLOEXEC) to atomically duplicate the file
descriptor and mark is as close-on-exec instead of dup2 & fcntl.

The dup3 system call first appeared in OpenBSD 5.7.

Change-Id: Ic06c2c7089dcdbd931ee24e5e8c316879d81474e
Reviewed-on: https://go-review.googlesource.com/c/go/+/389974
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/exec_bsd.go

@@ -181,18 +181,17 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	// 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 {
-		switch runtime.GOOS {
-		case "netbsd":
+		if runtime.GOOS == "netbsd" || (runtime.GOOS == "openbsd" && runtime.GOARCH == "mips64") {
 			_, _, err1 = RawSyscall(_SYS_DUP3, uintptr(pipe), uintptr(nextfd), O_CLOEXEC)
-			if err1 != 0 {
-				goto childerror
-			}
-		default:
+		} else {
 			_, _, err1 = RawSyscall(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
 			if err1 != 0 {
 				goto childerror
 			}
-			RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+		}
+		if err1 != 0 {
+			goto childerror
 		}
 		pipe = nextfd
 		nextfd++
@@ -202,18 +201,17 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 			if nextfd == pipe { // don't stomp on pipe
 				nextfd++
 			}
-			switch runtime.GOOS {
-			case "netbsd":
+			if runtime.GOOS == "netbsd" || (runtime.GOOS == "openbsd" && runtime.GOARCH == "mips64") {
 				_, _, err1 = RawSyscall(_SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC)
-				if err1 != 0 {
-					goto childerror
-				}
-			default:
+			} else {
 				_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
 				if err1 != 0 {
 					goto childerror
 				}
-				RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+				_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+			}
+			if err1 != 0 {
+				goto childerror
 			}
 			fd[i] = nextfd
 			nextfd++

src/syscall/exec_libc2.go

@@ -8,6 +8,7 @@ package syscall
 
 import (
 	"internal/abi"
+	"runtime"
 	"unsafe"
 )
 
@@ -180,11 +181,18 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	// 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(abi.FuncPCABI0(libc_dup2_trampoline), uintptr(pipe), uintptr(nextfd), 0)
+		if runtime.GOOS == "openbsd" {
+			_, _, err1 = rawSyscall(dupTrampoline, uintptr(pipe), uintptr(nextfd), O_CLOEXEC)
+		} else {
+			_, _, err1 = rawSyscall(dupTrampoline, uintptr(pipe), uintptr(nextfd), 0)
+			if err1 != 0 {
+				goto childerror
+			}
+			_, _, err1 = rawSyscall(abi.FuncPCABI0(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+		}
 		if err1 != 0 {
 			goto childerror
 		}
-		rawSyscall(abi.FuncPCABI0(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
 		pipe = nextfd
 		nextfd++
 	}
@@ -193,11 +201,18 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 			if nextfd == pipe { // don't stomp on pipe
 				nextfd++
 			}
-			_, _, err1 = rawSyscall(abi.FuncPCABI0(libc_dup2_trampoline), uintptr(fd[i]), uintptr(nextfd), 0)
+			if runtime.GOOS == "openbsd" {
+				_, _, err1 = rawSyscall(dupTrampoline, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC)
+			} else {
+				_, _, err1 = rawSyscall(dupTrampoline, uintptr(fd[i]), uintptr(nextfd), 0)
+				if err1 != 0 {
+					goto childerror
+				}
+				_, _, err1 = rawSyscall(abi.FuncPCABI0(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+			}
 			if err1 != 0 {
 				goto childerror
 			}
-			rawSyscall(abi.FuncPCABI0(libc_fcntl_trampoline), uintptr(nextfd), F_SETFD, FD_CLOEXEC)
 			fd[i] = nextfd
 			nextfd++
 		}

src/syscall/syscall_darwin.go

@@ -17,6 +17,8 @@ import (
 	"unsafe"
 )
 
+var dupTrampoline = abi.FuncPCABI0(libc_dup2_trampoline)
+
 type SockaddrDatalink struct {
 	Len    uint8
 	Family uint8

src/syscall/syscall_openbsd.go

@@ -136,6 +136,7 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, err error) {
 //sys	Close(fd int) (err error)
 //sys	Dup(fd int) (nfd int, err error)
 //sys	Dup2(from int, to int) (err error)
+//sys	dup3(from int, to int, flags int) (err error)
 //sys	Fchdir(fd int) (err error)
 //sys	Fchflags(fd int, flags int) (err error)
 //sys	Fchmod(fd int, mode uint32) (err error)

src/syscall/syscall_openbsd_libc.go

@@ -10,6 +10,8 @@ import (
 	"internal/abi"
 )
 
+var dupTrampoline = abi.FuncPCABI0(libc_dup3_trampoline)
+
 func init() {
 	execveOpenBSD = execve
 }

src/syscall/syscall_openbsd_mips64.go

@@ -4,7 +4,7 @@
 
 package syscall
 
-const _SYS_DUP3 = 0
+const _SYS_DUP3 = SYS_DUP3
 
 func setTimespec(sec, nsec int64) Timespec {
 	return Timespec{Sec: sec, Nsec: nsec}

src/syscall/zsyscall_openbsd_386.go

@@ -551,6 +551,20 @@ func libc_dup2_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func dup3(from int, to int, flags int) (err error) {
+	_, _, e1 := syscall(abi.FuncPCABI0(libc_dup3_trampoline), uintptr(from), uintptr(to), uintptr(flags))
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+func libc_dup3_trampoline()
+
+//go:cgo_import_dynamic libc_dup3 dup3 "libc.so"
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchdir(fd int) (err error) {
 	_, _, e1 := syscall(abi.FuncPCABI0(libc_fchdir_trampoline), uintptr(fd), 0, 0)
 	if e1 != 0 {

src/syscall/zsyscall_openbsd_386.s

@@ -69,6 +69,8 @@ TEXT ·libc_dup_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup(SB)
 TEXT ·libc_dup2_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup2(SB)
+TEXT ·libc_dup3_trampoline(SB),NOSPLIT,$0-0
+	JMP	libc_dup3(SB)
 TEXT ·libc_fchdir_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_fchdir(SB)
 TEXT ·libc_fchflags_trampoline(SB),NOSPLIT,$0-0

src/syscall/zsyscall_openbsd_amd64.go

@@ -551,6 +551,20 @@ func libc_dup2_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func dup3(from int, to int, flags int) (err error) {
+	_, _, e1 := syscall(abi.FuncPCABI0(libc_dup3_trampoline), uintptr(from), uintptr(to), uintptr(flags))
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+func libc_dup3_trampoline()
+
+//go:cgo_import_dynamic libc_dup3 dup3 "libc.so"
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchdir(fd int) (err error) {
 	_, _, e1 := syscall(abi.FuncPCABI0(libc_fchdir_trampoline), uintptr(fd), 0, 0)
 	if e1 != 0 {

src/syscall/zsyscall_openbsd_amd64.s

@@ -69,6 +69,8 @@ TEXT ·libc_dup_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup(SB)
 TEXT ·libc_dup2_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup2(SB)
+TEXT ·libc_dup3_trampoline(SB),NOSPLIT,$0-0
+	JMP	libc_dup3(SB)
 TEXT ·libc_fchdir_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_fchdir(SB)
 TEXT ·libc_fchflags_trampoline(SB),NOSPLIT,$0-0

src/syscall/zsyscall_openbsd_arm.go

@@ -551,6 +551,20 @@ func libc_dup2_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func dup3(from int, to int, flags int) (err error) {
+	_, _, e1 := syscall(abi.FuncPCABI0(libc_dup3_trampoline), uintptr(from), uintptr(to), uintptr(flags))
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+func libc_dup3_trampoline()
+
+//go:cgo_import_dynamic libc_dup3 dup3 "libc.so"
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchdir(fd int) (err error) {
 	_, _, e1 := syscall(abi.FuncPCABI0(libc_fchdir_trampoline), uintptr(fd), 0, 0)
 	if e1 != 0 {

src/syscall/zsyscall_openbsd_arm.s

@@ -69,6 +69,8 @@ TEXT ·libc_dup_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup(SB)
 TEXT ·libc_dup2_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup2(SB)
+TEXT ·libc_dup3_trampoline(SB),NOSPLIT,$0-0
+	JMP	libc_dup3(SB)
 TEXT ·libc_fchdir_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_fchdir(SB)
 TEXT ·libc_fchflags_trampoline(SB),NOSPLIT,$0-0

src/syscall/zsyscall_openbsd_arm64.go

@@ -551,6 +551,20 @@ func libc_dup2_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func dup3(from int, to int, flags int) (err error) {
+	_, _, e1 := syscall(abi.FuncPCABI0(libc_dup3_trampoline), uintptr(from), uintptr(to), uintptr(flags))
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+func libc_dup3_trampoline()
+
+//go:cgo_import_dynamic libc_dup3 dup3 "libc.so"
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Fchdir(fd int) (err error) {
 	_, _, e1 := syscall(abi.FuncPCABI0(libc_fchdir_trampoline), uintptr(fd), 0, 0)
 	if e1 != 0 {

src/syscall/zsyscall_openbsd_arm64.s

@@ -69,6 +69,8 @@ TEXT ·libc_dup_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup(SB)
 TEXT ·libc_dup2_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_dup2(SB)
+TEXT ·libc_dup3_trampoline(SB),NOSPLIT,$0-0
+	JMP	libc_dup3(SB)
 TEXT ·libc_fchdir_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_fchdir(SB)
 TEXT ·libc_fchflags_trampoline(SB),NOSPLIT,$0-0