snapshot: sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1

Содержимое пина, зафиксированного в go.mod sing-box-lx, одним коммитом
без истории. Полная история SagerNet/gvisor — 1.45 ГБ и клонируется в
каждой CI-джобе; наша дельта — одна вставка в одну функцию, история для
неё не нужна.

Module path github.com/sagernet/gvisor сохранён намеренно: на него
опирается replace-директива суперпроекта.

Патч поверх — отдельным коммитом, чтобы дельта читалась одним git show
и переносилась на новый пин копированием.

SPECS/TASKS/048-GVISOR_HANDSHAKE_NIL_CRASH

pkg/tcpip/link/loopback/loopback.go

@@ -0,0 +1,146 @@
+// Copyright 2018 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 loopback provides the implementation of loopback data-link layer
+// endpoints. Such endpoints just turn outbound packets into inbound ones.
+//
+// Loopback endpoints can be used in the networking stack by calling New() to
+// create a new endpoint, and then passing it as an argument to
+// Stack.CreateNIC().
+package loopback
+
+import (
+	"github.com/sagernet/gvisor/pkg/tcpip"
+	"github.com/sagernet/gvisor/pkg/tcpip/header"
+	"github.com/sagernet/gvisor/pkg/tcpip/stack"
+)
+
+const (
+	loopbackMTU = 65536
+)
+
+// +stateify savable
+type endpoint struct {
+	mu endpointRWMutex `state:"nosave"`
+	// +checklocks:mu
+	dispatcher stack.NetworkDispatcher
+	// +checklocks:mu
+	addr tcpip.LinkAddress
+	// +checklocks:mu
+	mtu uint32
+}
+
+// New creates a new loopback endpoint. This link-layer endpoint just turns
+// outbound packets into inbound packets.
+func New() stack.LinkEndpoint {
+	return &endpoint{
+		mtu: loopbackMTU,
+	}
+}
+
+// Attach implements stack.LinkEndpoint.Attach. It just saves the stack network-
+// layer dispatcher for later use when packets need to be dispatched.
+func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.dispatcher = dispatcher
+}
+
+// IsAttached implements stack.LinkEndpoint.IsAttached.
+func (e *endpoint) IsAttached() bool {
+	e.mu.RLock()
+	defer e.mu.RUnlock()
+	return e.dispatcher != nil
+}
+
+// MTU implements stack.LinkEndpoint.MTU.
+func (e *endpoint) MTU() uint32 {
+	e.mu.RLock()
+	defer e.mu.RUnlock()
+	return e.mtu
+}
+
+// SetMTU implements stack.LinkEndpoint.SetMTU. It has no impact.
+func (e *endpoint) SetMTU(mtu uint32) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.mtu = mtu
+}
+
+// Capabilities implements stack.LinkEndpoint.Capabilities. Loopback advertises
+// itself as supporting checksum offload, but in reality it's just omitted.
+func (*endpoint) Capabilities() stack.LinkEndpointCapabilities {
+	return stack.CapabilityRXChecksumOffload | stack.CapabilityTXChecksumOffload | stack.CapabilitySaveRestore | stack.CapabilityLoopback
+}
+
+// MaxHeaderLength implements stack.LinkEndpoint.MaxHeaderLength. Given that the
+// loopback interface doesn't have a header, it just returns 0.
+func (*endpoint) MaxHeaderLength() uint16 {
+	return 0
+}
+
+// LinkAddress returns the link address of this endpoint.
+func (e *endpoint) LinkAddress() tcpip.LinkAddress {
+	e.mu.RLock()
+	defer e.mu.RUnlock()
+	return e.addr
+}
+
+// SetLinkAddress implements stack.LinkEndpoint.SetLinkAddress.
+func (e *endpoint) SetLinkAddress(addr tcpip.LinkAddress) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.addr = addr
+}
+
+// Wait implements stack.LinkEndpoint.Wait.
+func (*endpoint) Wait() {}
+
+// WritePackets implements stack.LinkEndpoint.WritePackets. If the endpoint is
+// not attached, the packets are not delivered.
+func (e *endpoint) WritePackets(pkts stack.PacketBufferList) (int, tcpip.Error) {
+	e.mu.RLock()
+	d := e.dispatcher
+	e.mu.RUnlock()
+	for _, pkt := range pkts.AsSlice() {
+		// In order to properly loop back to the inbound side we must create a
+		// fresh packet that only contains the underlying payload with no headers
+		// or struct fields set.
+		newPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+			Payload: pkt.ToBuffer(),
+		})
+		if d != nil {
+			d.DeliverNetworkPacket(pkt.NetworkProtocolNumber, newPkt)
+		}
+		newPkt.DecRef()
+	}
+	return pkts.Len(), nil
+}
+
+// ARPHardwareType implements stack.LinkEndpoint.ARPHardwareType.
+func (*endpoint) ARPHardwareType() header.ARPHardwareType {
+	return header.ARPHardwareLoopback
+}
+
+// AddHeader implements stack.LinkEndpoint.
+func (*endpoint) AddHeader(*stack.PacketBuffer) {}
+
+// ParseHeader implements stack.LinkEndpoint.
+func (*endpoint) ParseHeader(*stack.PacketBuffer) bool { return true }
+
+// Close implements stack.LinkEndpoint.
+func (*endpoint) Close() {}
+
+// SetOnCloseAction implements stack.LinkEndpoint.
+func (*endpoint) SetOnCloseAction(func()) {}