wip

internal/firewall/nftables/input.go

@@ -0,0 +1,170 @@
+package nftables
+
+import (
+	"context"
+	"fmt"
+	"net/netip"
+
+	"github.com/google/nftables"
+	"github.com/google/nftables/expr"
+)
+
+func (f *Firewall) AcceptInputThroughInterface(_ context.Context, intf string) error {
+	f.mutex.Lock()
+	defer f.mutex.Unlock()
+
+	conn, err := nftables.New()
+	if err != nil {
+		return fmt.Errorf("creating nftables connection: %w", err)
+	}
+
+	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
+
+	rule := &nftables.Rule{
+		Table: table,
+		Chain: inputChain,
+		Exprs: []expr.Any{
+			&expr.Meta{
+				Key:      expr.MetaKeyIIFNAME,
+				Register: 1,
+			},
+			&expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     []byte(intf + "\x00"),
+			},
+			&expr.Verdict{
+				Kind: expr.VerdictAccept,
+			},
+		},
+	}
+
+	conn.AddRule(rule)
+
+	err = conn.Flush()
+	if err != nil {
+		return fmt.Errorf("flushing: %w", err)
+	}
+
+	return nil
+}
+
+// AcceptInputToPort accepts incoming traffic on the specified port, for both TCP and UDP
+// protocols, on the interface intf. If intf is empty or "*", the interface is not used as a filter.
+// If remove is true, the rule is removed instead of added. This is used for port forwarding, with
+// intf set to the VPN tunnel interface.
+func (f *Firewall) AcceptInputToPort(_ context.Context, intf string, port uint16, remove bool) error {
+	f.mutex.Lock()
+	defer f.mutex.Unlock()
+
+	conn, err := nftables.New()
+	if err != nil {
+		return fmt.Errorf("creating nftables connection: %w", err)
+	}
+
+	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
+	portBytes := []byte{byte(port >> 8), byte(port)} //nolint:mnd
+	const tcp, udp uint8 = 6, 17
+	protocols := []uint8{tcp, udp}
+
+	for _, protocol := range protocols {
+		const maxExprsLen = 7
+		exprs := make([]expr.Any, 0, maxExprsLen)
+		if intf != "" && intf != "*" {
+			exprs = append(exprs,
+				&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+				&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte(intf + "\x00")},
+			)
+		}
+		exprs = append(exprs,
+			&expr.Payload{DestRegister: 1, Base: expr.PayloadBaseNetworkHeader, Offset: 9, Len: 1}, //nolint:mnd
+			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte{protocol}},
+			&expr.Payload{DestRegister: 1, Base: expr.PayloadBaseTransportHeader, Offset: 2, Len: 2}, //nolint:mnd
+			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: portBytes},
+			&expr.Verdict{Kind: expr.VerdictAccept},
+		)
+
+		rule := &nftables.Rule{
+			Table: table,
+			Chain: inputChain,
+			Exprs: exprs,
+		}
+
+		if !remove {
+			conn.AddRule(rule)
+			f.rules = append(f.rules, rule)
+			continue
+		}
+		err = f.deleteRule(conn, rule)
+		if err != nil {
+			return fmt.Errorf("deleting rule: %w", err)
+		}
+	}
+
+	err = conn.Flush()
+	if err != nil {
+		f.rules = f.rules[:len(f.rules)-len(protocols)]
+		return fmt.Errorf("flushing: %w", err)
+	}
+
+	return nil
+}
+
+func (f *Firewall) AcceptInputToSubnet(_ context.Context, intf string, subnet netip.Prefix) error {
+	f.mutex.Lock()
+	defer f.mutex.Unlock()
+
+	conn, err := nftables.New()
+	if err != nil {
+		return fmt.Errorf("creating nftables connection: %w", err)
+	}
+
+	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
+
+	const maxExprsLen = 5
+	exprs := make([]expr.Any, 0, maxExprsLen)
+
+	if intf != "" && intf != "*" {
+		exprs = append(exprs,
+			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte(intf + "\x00")},
+		)
+	}
+
+	var payloadOffset uint32
+	if subnet.Addr().Is4() {
+		payloadOffset = 16
+	} else {
+		payloadOffset = 24
+	}
+
+	exprs = append(exprs,
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseNetworkHeader,
+			Offset:       payloadOffset,
+			Len:          uint32(len(subnet.Addr().AsSlice())), //nolint:gosec
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     subnet.Addr().AsSlice(),
+		},
+		&expr.Verdict{Kind: expr.VerdictAccept},
+	)
+
+	rule := &nftables.Rule{
+		Table: table,
+		Chain: inputChain,
+		Exprs: exprs,
+	}
+
+	conn.AddRule(rule)
+
+	err = conn.Flush()
+	if err != nil {
+		return fmt.Errorf("flushing: %w", err)
+	}
+
+	return nil
+}