net: pass MSG_CMSG_CLOEXEC flag in ReadMsgUnix

As mentioned in golang#42765, calling "recvmsg" syscall on Linux should come
with "MSG_CMSG_CLOEXEC" flag.

For other systems which not supports "MSG_CMSG_CLOEXEC". ReadMsgUnix()
would check the header. If the header type is "syscall.SCM_RIGHTS",
then ReadMsgUnix() would parse the SocketControlMessage and call each
fd with "syscall.CloseOnExec"

Fixes golang#42765

src/internal/poll/fd_unix.go

@@ -231,7 +231,7 @@ func (fd *FD) ReadFrom(p []byte) (int, syscall.Sockaddr, error) {
 }
 
 // ReadMsg wraps the recvmsg network call.
-func (fd *FD) ReadMsg(p []byte, oob []byte) (int, int, int, syscall.Sockaddr, error) {
+func (fd *FD) ReadMsg(p []byte, oob []byte, flags int) (int, int, int, syscall.Sockaddr, error) {
 	if err := fd.readLock(); err != nil {
 		return 0, 0, 0, nil, err
 	}
@@ -240,7 +240,7 @@ func (fd *FD) ReadMsg(p []byte, oob []byte) (int, int, int, syscall.Sockaddr, er
 		return 0, 0, 0, nil, err
 	}
 	for {
-		n, oobn, flags, sa, err := syscall.Recvmsg(fd.Sysfd, p, oob, 0)
+		n, oobn, sysflags, sa, err := syscall.Recvmsg(fd.Sysfd, p, oob, flags)
 		if err != nil {
 			if err == syscall.EINTR {
 				continue
@@ -253,7 +253,7 @@ func (fd *FD) ReadMsg(p []byte, oob []byte) (int, int, int, syscall.Sockaddr, er
 			}
 		}
 		err = fd.eofError(n, err)
-		return n, oobn, flags, sa, err
+		return n, oobn, sysflags, sa, err
 	}
 }
 

src/internal/poll/fd_windows.go

@@ -1013,7 +1013,7 @@ func sockaddrToRaw(sa syscall.Sockaddr) (unsafe.Pointer, int32, error) {
 }
 
 // ReadMsg wraps the WSARecvMsg network call.
-func (fd *FD) ReadMsg(p []byte, oob []byte) (int, int, int, syscall.Sockaddr, error) {
+func (fd *FD) ReadMsg(p []byte, oob []byte, flags int) (int, int, int, syscall.Sockaddr, error) {
 	if err := fd.readLock(); err != nil {
 		return 0, 0, 0, nil, err
 	}
@@ -1028,6 +1028,7 @@ func (fd *FD) ReadMsg(p []byte, oob []byte) (int, int, int, syscall.Sockaddr, er
 	o.rsa = new(syscall.RawSockaddrAny)
 	o.msg.Name = (syscall.Pointer)(unsafe.Pointer(o.rsa))
 	o.msg.Namelen = int32(unsafe.Sizeof(*o.rsa))
+	o.msg.Flags = uint32(flags)
 	n, err := execIO(o, func(o *operation) error {
 		return windows.WSARecvMsg(o.fd.Sysfd, &o.msg, &o.qty, &o.o, nil)
 	})

src/net/fd_posix.go

@@ -64,10 +64,10 @@ func (fd *netFD) readFrom(p []byte) (n int, sa syscall.Sockaddr, err error) {
 	return n, sa, wrapSyscallError(readFromSyscallName, err)
 }
 
-func (fd *netFD) readMsg(p []byte, oob []byte) (n, oobn, flags int, sa syscall.Sockaddr, err error) {
-	n, oobn, flags, sa, err = fd.pfd.ReadMsg(p, oob)
+func (fd *netFD) readMsg(p []byte, oob []byte, flags int) (n, oobn, retflags int, sa syscall.Sockaddr, err error) {
+	n, oobn, retflags, sa, err = fd.pfd.ReadMsg(p, oob, flags)
 	runtime.KeepAlive(fd)
-	return n, oobn, flags, sa, wrapSyscallError(readMsgSyscallName, err)
+	return n, oobn, retflags, sa, wrapSyscallError(readMsgSyscallName, err)
 }
 
 func (fd *netFD) Write(p []byte) (nn int, err error) {

src/net/iprawsock_posix.go

@@ -75,7 +75,7 @@ func stripIPv4Header(n int, b []byte) int {
 
 func (c *IPConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *IPAddr, err error) {
 	var sa syscall.Sockaddr
-	n, oobn, flags, sa, err = c.fd.readMsg(b, oob)
+	n, oobn, flags, sa, err = c.fd.readMsg(b, oob, 0)
 	switch sa := sa.(type) {
 	case *syscall.SockaddrInet4:
 		addr = &IPAddr{IP: sa.Addr[0:]}

src/net/net_fake.go

@@ -268,7 +268,7 @@ func (fd *netFD) readFrom(p []byte) (n int, sa syscall.Sockaddr, err error) {
 	return 0, nil, syscall.ENOSYS
 }
 
-func (fd *netFD) readMsg(p []byte, oob []byte) (n, oobn, flags int, sa syscall.Sockaddr, err error) {
+func (fd *netFD) readMsg(p []byte, oob []byte, flags int) (n, oobn, retflags int, sa syscall.Sockaddr, err error) {
 	return 0, 0, 0, nil, syscall.ENOSYS
 }
 

src/net/udpsock_posix.go

@@ -56,7 +56,7 @@ func (c *UDPConn) readFrom(b []byte, addr *UDPAddr) (int, *UDPAddr, error) {
 
 func (c *UDPConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *UDPAddr, err error) {
 	var sa syscall.Sockaddr
-	n, oobn, flags, sa, err = c.fd.readMsg(b, oob)
+	n, oobn, flags, sa, err = c.fd.readMsg(b, oob, 0)
 	switch sa := sa.(type) {
 	case *syscall.SockaddrInet4:
 		addr = &UDPAddr{IP: sa.Addr[0:], Port: sa.Port}

src/net/unixsock_posix.go

@@ -111,18 +111,6 @@ func (c *UnixConn) readFrom(b []byte) (int, *UnixAddr, error) {
 	return n, addr, err
 }
 
-func (c *UnixConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *UnixAddr, err error) {
-	var sa syscall.Sockaddr
-	n, oobn, flags, sa, err = c.fd.readMsg(b, oob)
-	switch sa := sa.(type) {
-	case *syscall.SockaddrUnix:
-		if sa.Name != "" {
-			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
-		}
-	}
-	return
-}
-
 func (c *UnixConn) writeTo(b []byte, addr *UnixAddr) (int, error) {
 	if c.fd.isConnected {
 		return 0, ErrWriteToConnected

src/net/unixsock_readmsg.go

@@ -0,0 +1,23 @@
+// 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 net
+
+import (
+	"syscall"
+)
+
+func (c *UnixConn) readMsg(b, oob []byte) (n, oobn, flags int, addr *UnixAddr, err error) {
+	var sa syscall.Sockaddr
+	n, oobn, flags, sa, err = c.fd.readMsg(b, oob, readMsgFlags)
+	setCloseOnExec(oob[:oobn])
+
+	switch sa := sa.(type) {
+	case *syscall.SockaddrUnix:
+		if sa.Name != "" {
+			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
+		}
+	}
+	return
+}

src/net/unixsock_readmsg_linux.go

@@ -0,0 +1,18 @@
+// 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.
+
+//go:build linux
+// +build linux
+
+package net
+
+import (
+	"syscall"
+)
+
+const readMsgFlags int = syscall.MSG_CMSG_CLOEXEC
+
+func setCloseOnExec(oob []byte) {
+	return
+}

src/net/unixsock_readmsg_other.go

@@ -0,0 +1,14 @@
+// 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.
+
+//go:build (js && wasm) || windows
+// +build js,wasm windows
+
+package net
+
+const readMsgFlags int = 0
+
+func setCloseOnExec(oob []byte) {
+	return
+}

src/net/unixsock_readmsg_posix.go

@@ -0,0 +1,37 @@
+// 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.
+
+//go:build aix || darwin || dragonfly || freebsd || netbsd || openbsd || solaris
+// +build aix darwin dragonfly freebsd netbsd openbsd solaris
+
+package net
+
+import (
+	"syscall"
+)
+
+const readMsgFlags int = 0
+
+func setCloseOnExec(oob []byte) {
+	if oobn <= 0 {
+		return
+	}
+
+	scms, err := syscall.ParseSocketControlMessage(oob)
+	if err != nil {
+		return
+	}
+
+	for _, scm := range scms {
+		if scm.Header.Level == syscall.SOL_SOCKET && scm.Header.Type == syscall.SCM_RIGHTS {
+			fds, err := syscall.ParseUnixRights(&scm)
+			if err != nil {
+				continue
+			}
+			for _, fd := range fds {
+				syscall.CloseOnExec(fd)
+			}
+		}
+	}
+}

src/net/unixsock_readmsg_test.go

@@ -0,0 +1,105 @@
+// 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.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package net
+
+import (
+	"os"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func TestUnixConnReadMsgUnixSCMRightsCloseOnExec(t *testing.T) {
+	if !testableNetwork("unix") {
+		t.Skip("not unix system")
+	}
+
+	scmFile, err := os.Open(os.DevNull)
+	if err != nil {
+		t.Fatalf("file open: %v", err)
+	}
+	defer scmFile.Close()
+
+	rights := syscall.UnixRights(int(scmFile.Fd()))
+	fds, err := syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		t.Fatalf("Socketpair: %v", err)
+	}
+
+	writeFile := os.NewFile(uintptr(fds[0]), "write-socket")
+	defer writeFile.Close()
+	readFile := os.NewFile(uintptr(fds[1]), "read-socket")
+	defer readFile.Close()
+
+	cw, err := FileConn(writeFile)
+	if err != nil {
+		t.Fatalf("FileConn: %v", err)
+	}
+	defer cw.Close()
+	cr, err := FileConn(readFile)
+	if err != nil {
+		t.Fatalf("FileConn: %v", err)
+	}
+	defer cr.Close()
+
+	ucw, ok := cw.(*UnixConn)
+	if !ok {
+		t.Fatalf("got %T; want UnixConn", cw)
+	}
+	ucr, ok := cr.(*UnixConn)
+	if !ok {
+		t.Fatalf("got %T; want UnixConn", cr)
+	}
+
+	oob := make([]byte, syscall.CmsgSpace(4))
+	err = ucw.SetWriteDeadline(time.Now().Add(5 * time.Second))
+	if err != nil {
+		t.Fatalf("Can't set unix connection timeout: %v", err)
+	}
+	_, _, err = ucw.WriteMsgUnix(nil, rights, nil)
+	if err != nil {
+		t.Fatalf("UnixConn readMsg: %v", err)
+	}
+	err = ucr.SetReadDeadline(time.Now().Add(5 * time.Second))
+	if err != nil {
+		t.Fatalf("Can't set unix connection timeout: %v", err)
+	}
+	_, oobn, _, _, err := ucr.ReadMsgUnix(nil, oob)
+	if err != nil {
+		t.Fatalf("UnixConn readMsg: %v", err)
+	}
+
+	scms, err := syscall.ParseSocketControlMessage(oob[:oobn])
+	if err != nil {
+		t.Fatalf("ParseSocketControlMessage: %v", err)
+	}
+	if len(scms) != 1 {
+		t.Fatalf("got scms = %#v; expected 1 SocketControlMessage", scms)
+	}
+	scm := scms[0]
+	gotFds, err := syscall.ParseUnixRights(&scm)
+	if err != nil {
+		t.Fatalf("syscall.ParseUnixRights: %v", err)
+	}
+	if len(gotFds) != 1 {
+		t.Fatalf("got FDs %#v: wanted only 1 fd", gotFds)
+	}
+	defer func() {
+		if err := syscall.Close(int(gotFds[0])); err != nil {
+			t.Fatalf("fail to close gotFds: %v", err)
+		}
+	}()
+
+	flags, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(gotFds[0]), uintptr(syscall.F_GETFD), 0)
+	if errno != 0 {
+		t.Fatalf("Can't get flags of fd:%#v, with err:%v", gotFds[0], errno)
+	}
+	if flags&syscall.FD_CLOEXEC == 0 {
+		t.Fatalf("got flags %#x, want %#x (FD_CLOEXEC) set", flags, syscall.FD_CLOEXEC)
+	}
+}

src/syscall/creds_test.go

@@ -104,8 +104,8 @@ func TestSCMCredentials(t *testing.T) {
 		if err != nil {
 			t.Fatalf("ReadMsgUnix: %v", err)
 		}
-		if flags != 0 {
-			t.Fatalf("ReadMsgUnix flags = 0x%x, want 0", flags)
+		if flags != syscall.MSG_CMSG_CLOEXEC {
+			t.Fatalf("ReadMsgUnix flags = %#x, want %#x (MSG_CMSG_CLOEXEC)", flags, syscall.MSG_CMSG_CLOEXEC)
 		}
 		if n != tt.dataLen {
 			t.Fatalf("ReadMsgUnix n = %d, want %d", n, tt.dataLen)