From 35c1a1f38d6b28d51f00fd5dbf7777475c89aa54 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maxime=20Soul=C3=A9?= <btik-git@scoubidou.com>
Date: Fri, 26 Apr 2024 16:59:20 +0200
Subject: [PATCH] Add (*afpacket.TPacket).SetPromiscuous
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Closes #564.

Signed-off-by: Maxime Soulé <btik-git@scoubidou.com>
---
 afpacket/afpacket.go | 45 ++++++++++++++++++++++++++++++++------------
 afpacket/options.go  |  2 ++
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/afpacket/afpacket.go b/afpacket/afpacket.go
index 6600ae25e..f7921dd66 100644
--- a/afpacket/afpacket.go
+++ b/afpacket/afpacket.go
@@ -135,20 +135,20 @@ type TPacket struct {
 
 var _ gopacket.ZeroCopyPacketDataSource = &TPacket{}
 
-// bindToInterface binds the TPacket socket to a particular named interface.
-func (h *TPacket) bindToInterface(ifaceName string) error {
-	ifIndex := 0
+// bindToInterface binds the TPacket socket to the configured interface.
+func (h *TPacket) bindToInterface() error {
+	h.opts.ifaceIdx = 0
 	// An empty string here means to listen to all interfaces
-	if ifaceName != "" {
-		iface, err := net.InterfaceByName(ifaceName)
+	if h.opts.iface != "" {
+		iface, err := net.InterfaceByName(h.opts.iface)
 		if err != nil {
 			return fmt.Errorf("InterfaceByName: %v", err)
 		}
-		ifIndex = iface.Index
+		h.opts.ifaceIdx = iface.Index
 	}
 	s := &unix.SockaddrLinklayer{
 		Protocol: htons(uint16(unix.ETH_P_ALL)),
-		Ifindex:  ifIndex,
+		Ifindex:  h.opts.ifaceIdx,
 	}
 	return unix.Bind(h.fd, s)
 }
@@ -242,7 +242,7 @@ func NewTPacket(opts ...interface{}) (h *TPacket, err error) {
 		return nil, err
 	}
 	h.fd = fd
-	if err = h.bindToInterface(h.opts.iface); err != nil {
+	if err = h.bindToInterface(); err != nil {
 		goto errlbl
 	}
 	if err = h.setRequestedTPacketVersion(); err != nil {
@@ -279,6 +279,26 @@ func (h *TPacket) SetEBPF(progFd int32) error {
 	return setsockopt(h.fd, unix.SOL_SOCKET, unix.SO_ATTACH_BPF, unsafe.Pointer(&progFd), 4)
 }
 
+// SetPromiscuous sets promiscous mode to the required value. If it is
+// enabled, traffic not destined for the interface will also be
+// captured.
+//
+// Non empty OptInterface options is required, otherwise an error is returned.
+func (h *TPacket) SetPromiscuous(on bool) error {
+	if h.opts.ifaceIdx == 0 {
+		return errors.New("SetPromiscuous needs non empty OptInterface option")
+	}
+	mreq := unix.PacketMreq{
+		Ifindex: int32(h.opts.ifaceIdx),
+		Type:    unix.PACKET_MR_PROMISC,
+	}
+	opt := unix.PACKET_DROP_MEMBERSHIP
+	if on {
+		opt = unix.PACKET_ADD_MEMBERSHIP
+	}
+	return unix.SetsockoptPacketMreq(h.fd, unix.SOL_PACKET, opt, &mreq)
+}
+
 func (h *TPacket) releaseCurrentPacket() error {
 	h.current.clearStatus()
 	h.offset++
@@ -293,10 +313,11 @@ func (h *TPacket) releaseCurrentPacket() error {
 // to old bytes when using ZeroCopyReadPacketData... if you need to keep data past
 // the next time you call ZeroCopyReadPacketData, use ReadPacketData, which copies
 // the bytes into a new buffer for you.
-//  tp, _ := NewTPacket(...)
-//  data1, _, _ := tp.ZeroCopyReadPacketData()
-//  // do everything you want with data1 here, copying bytes out of it if you'd like to keep them around.
-//  data2, _, _ := tp.ZeroCopyReadPacketData()  // invalidates bytes in data1
+//
+//	tp, _ := NewTPacket(...)
+//	data1, _, _ := tp.ZeroCopyReadPacketData()
+//	// do everything you want with data1 here, copying bytes out of it if you'd like to keep them around.
+//	data2, _, _ := tp.ZeroCopyReadPacketData()  // invalidates bytes in data1
 func (h *TPacket) ZeroCopyReadPacketData() (data []byte, ci gopacket.CaptureInfo, err error) {
 	h.mu.Lock()
 retry:
diff --git a/afpacket/options.go b/afpacket/options.go
index 3e305c4d6..44cea8db3 100644
--- a/afpacket/options.go
+++ b/afpacket/options.go
@@ -4,6 +4,7 @@
 // that can be found in the LICENSE file in the root of the source
 // tree.
 
+//go:build linux
 // +build linux
 
 package afpacket
@@ -126,6 +127,7 @@ type options struct {
 	version        OptTPacketVersion
 	socktype       OptSocketType
 	iface          string
+	ifaceIdx       int
 }
 
 var defaultOpts = options{