iptables: support SO_ORIGINAL_DST

Envoy (#170) uses this to get the original destination of redirected
packets.

1 files changed, 63 insertions, 0 deletions

diff --git a/test/iptables/iptables_unsafe.go b/test/iptables/iptables_unsafe.go
new file mode 100644
index 000000000..bd85a8fea
--- /dev/null
+++ b/test/iptables/iptables_unsafe.go
@@ -0,0 +1,63 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iptables
+
+import (
+	"fmt"
+	"syscall"
+	"unsafe"
+)
+
+type originalDstError struct {
+	errno syscall.Errno
+}
+
+func (e originalDstError) Error() string {
+	return fmt.Sprintf("errno (%d) when calling getsockopt(SO_ORIGINAL_DST): %v", int(e.errno), e.errno.Error())
+}
+
+// SO_ORIGINAL_DST gets the original destination of a redirected packet via
+// getsockopt.
+const SO_ORIGINAL_DST = 80
+
+func originalDestination4(connfd int) (syscall.RawSockaddrInet4, error) {
+	var addr syscall.RawSockaddrInet4
+	var addrLen uint32 = syscall.SizeofSockaddrInet4
+	if errno := originalDestination(connfd, syscall.SOL_IP, unsafe.Pointer(&addr), &addrLen); errno != 0 {
+		return syscall.RawSockaddrInet4{}, originalDstError{errno}
+	}
+	return addr, nil
+}
+
+func originalDestination6(connfd int) (syscall.RawSockaddrInet6, error) {
+	var addr syscall.RawSockaddrInet6
+	var addrLen uint32 = syscall.SizeofSockaddrInet6
+	if errno := originalDestination(connfd, syscall.SOL_IPV6, unsafe.Pointer(&addr), &addrLen); errno != 0 {
+		return syscall.RawSockaddrInet6{}, originalDstError{errno}
+	}
+	return addr, nil
+}
+
+func originalDestination(connfd int, level uintptr, optval unsafe.Pointer, optlen *uint32) syscall.Errno {
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_GETSOCKOPT,
+		uintptr(connfd),
+		level,
+		SO_ORIGINAL_DST,
+		uintptr(optval),
+		uintptr(unsafe.Pointer(optlen)),
+		0)
+	return errno
+}