net: filter GetAddr netlink requests by interface index

src/net/interface_linux.go

@@ -6,6 +6,7 @@ package net
 
 import (
 	"os"
+	"sync"
 	"syscall"
 	"unsafe"
 )
@@ -121,7 +122,11 @@ func linkFlags(rawFlags uint32) Flags {
 // network interfaces. Otherwise it returns addresses for a specific
 // interface.
 func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
-	tab, err := syscall.NetlinkRIB(syscall.RTM_GETADDR, syscall.AF_UNSPEC)
+	var ifindex int
+	if ifi != nil {
+		ifindex = ifi.Index
+	}
+	tab, err := netlinkRIB(getAddrRequest(syscall.AF_UNSPEC, ifindex))
 	if err != nil {
 		return nil, os.NewSyscallError("netlinkrib", err)
 	}
@@ -255,3 +260,87 @@ func parseProcNetIGMP6(path string, ifi *Interface) []Addr {
 	}
 	return ifmat
 }
+
+func getAddrRequest(family, ifindex int) []byte {
+	reqLen := syscall.NLMSG_HDRLEN + syscall.SizeofIfAddrmsg
+	req := make([]byte, reqLen)
+	h := (*syscall.NlMsghdr)(unsafe.Pointer(&req[0]))
+	h.Len = uint32(reqLen)
+	h.Flags = uint16(syscall.NLM_F_REQUEST | syscall.NLM_F_DUMP)
+	h.Type = uint16(syscall.RTM_GETADDR)
+	h.Seq = uint32(1)
+	iam := (*syscall.IfAddrmsg)(unsafe.Pointer(&req[syscall.NLMSG_HDRLEN]))
+	iam.Family = uint8(family)
+	iam.Index = uint32(ifindex)
+	return req
+}
+
+var pageBufPool = &sync.Pool{New: func() any {
+	b := make([]byte, syscall.Getpagesize())
+	return &b
+}}
+
+// These constants aren't in the syscall package, which is frozen.
+// Values taken from golang.org/x/sys/unix.
+const (
+	_SOL_NETLINK            = 0x10e
+	_NETLINK_GET_STRICT_CHK = 0x0c
+)
+
+// Modified version of syscall.NetlinkRIB that sets NETLINK_GET_STRICT_CHK and
+// sends request bytes directly to the socket.
+func netlinkRIB(req []byte) ([]byte, error) {
+	s, err := syscall.Socket(syscall.AF_NETLINK, syscall.SOCK_RAW|syscall.SOCK_CLOEXEC, syscall.NETLINK_ROUTE)
+	if err != nil {
+		return nil, err
+	}
+	defer syscall.Close(s)
+	_ = syscall.SetsockoptInt(s, _SOL_NETLINK, _NETLINK_GET_STRICT_CHK, 1)
+	sa := &syscall.SockaddrNetlink{Family: syscall.AF_NETLINK}
+	if err := syscall.Bind(s, sa); err != nil {
+		return nil, err
+	}
+	if err := syscall.Sendto(s, req, 0, sa); err != nil {
+		return nil, err
+	}
+	lsa, err := syscall.Getsockname(s)
+	if err != nil {
+		return nil, err
+	}
+	lsanl, ok := lsa.(*syscall.SockaddrNetlink)
+	if !ok {
+		return nil, syscall.EINVAL
+	}
+	var tab []byte
+	rbNew := pageBufPool.Get().(*[]byte)
+	defer pageBufPool.Put(rbNew)
+done:
+	for {
+		rb := *rbNew
+		nr, _, err := syscall.Recvfrom(s, rb, 0)
+		if err != nil {
+			return nil, err
+		}
+		if nr < syscall.NLMSG_HDRLEN {
+			return nil, syscall.EINVAL
+		}
+		rb = rb[:nr]
+		tab = append(tab, rb...)
+		msgs, err := syscall.ParseNetlinkMessage(rb)
+		if err != nil {
+			return nil, err
+		}
+		for _, m := range msgs {
+			if m.Header.Seq != 1 || m.Header.Pid != lsanl.Pid {
+				return nil, syscall.EINVAL
+			}
+			if m.Header.Type == syscall.NLMSG_DONE {
+				break done
+			}
+			if m.Header.Type == syscall.NLMSG_ERROR {
+				return nil, syscall.EINVAL
+			}
+		}
+	}
+	return tab, nil
+}