Allow creating packet socket bound to any protocol

...even protocols the stack is unaware of.

While I am here, annotate checklocks on stack.packetEndpointList.

PiperOrigin-RevId: 397226754

pkg/tcpip/stack/nic.go

@@ -97,6 +97,8 @@ type packetEndpointList struct {
 	mu sync.RWMutex
 
 	// eps is protected by mu, but the contained PacketEndpoint values are not.
+	//
+	// +checklocks:mu
 	eps []PacketEndpoint
 }
 
@@ -117,6 +119,12 @@ func (p *packetEndpointList) remove(ep PacketEndpoint) {
 	}
 }
 
+func (p *packetEndpointList) len() int {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	return len(p.eps)
+}
+
 // forEach calls fn with each endpoints in p while holding the read lock on p.
 func (p *packetEndpointList) forEach(fn func(PacketEndpoint)) {
 	p.mu.RLock()
@@ -157,14 +165,8 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICC
 
 	resolutionRequired := ep.Capabilities()&CapabilityResolutionRequired != 0
 
-	// Register supported packet and network endpoint protocols.
-	for _, netProto := range header.Ethertypes {
-		nic.packetEPs.eps[netProto] = new(packetEndpointList)
-	}
 	for _, netProto := range stack.networkProtocols {
 		netNum := netProto.Number()
-		nic.packetEPs.eps[netNum] = new(packetEndpointList)
-
 		netEP := netProto.NewEndpoint(nic, nic)
 		nic.networkEndpoints[netNum] = netEP
 
@@ -974,7 +976,8 @@ func (n *nic) registerPacketEndpoint(netProto tcpip.NetworkProtocolNumber, ep Pa
 
 	eps, ok := n.packetEPs.eps[netProto]
 	if !ok {
-		return &tcpip.ErrNotSupported{}
+		eps = new(packetEndpointList)
+		n.packetEPs.eps[netProto] = eps
 	}
 	eps.add(ep)
 
@@ -990,6 +993,9 @@ func (n *nic) unregisterPacketEndpoint(netProto tcpip.NetworkProtocolNumber, ep
 		return
 	}
 	eps.remove(ep)
+	if eps.len() == 0 {
+		delete(n.packetEPs.eps, netProto)
+	}
 }
 
 // isValidForOutgoing returns true if the endpoint can be used to send out a

test/syscalls/BUILD

@@ -366,6 +366,10 @@ syscall_test(
     test = "//test/syscalls/linux:packet_socket_raw_test",
 )
 
+syscall_test(
+    test = "//test/syscalls/linux:packet_socket_test",
+)
+
 syscall_test(
     test = "//test/syscalls/linux:partial_bad_buffer_test",
 )

test/syscalls/linux/BUILD

@@ -7,6 +7,7 @@ package(
 
 exports_files(
     [
+        "packet_socket.cc",
         "packet_socket_dgram.cc",
         "packet_socket_raw.cc",
         "raw_socket.cc",
@@ -1480,6 +1481,20 @@ cc_binary(
     ],
 )
 
+cc_binary(
+    name = "packet_socket_test",
+    testonly = 1,
+    srcs = ["packet_socket.cc"],
+    linkstatic = 1,
+    deps = [
+        "//test/util:capability_util",
+        "//test/util:file_descriptor",
+        "//test/util:socket_util",
+        gtest,
+        "//test/util:test_main",
+    ],
+)
+
 cc_binary(
     name = "pty_test",
     testonly = 1,

test/syscalls/linux/packet_socket.cc

@@ -0,0 +1,60 @@
+// Copyright 2021 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.
+
+#include <net/if.h>
+#include <netinet/if_ether.h>
+
+#include <limits>
+
+#include "gtest/gtest.h"
+#include "test/util/capability_util.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/socket_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+using ::testing::Combine;
+using ::testing::Values;
+
+class PacketSocketTest : public ::testing::TestWithParam<std::tuple<int, int>> {
+ protected:
+  void SetUp() override {
+    if (!ASSERT_NO_ERRNO_AND_VALUE(HavePacketSocketCapability())) {
+      const auto [type, protocol] = GetParam();
+      ASSERT_THAT(socket(AF_PACKET, type, htons(protocol)),
+                  SyscallFailsWithErrno(EPERM));
+      GTEST_SKIP() << "Missing packet socket capability";
+    }
+  }
+};
+
+TEST_P(PacketSocketTest, Create) {
+  const auto [type, protocol] = GetParam();
+  FileDescriptor fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_PACKET, type, htons(protocol)));
+  EXPECT_GE(fd.get(), 0);
+}
+
+INSTANTIATE_TEST_SUITE_P(AllPacketSocketTests, PacketSocketTest,
+                         Combine(Values(SOCK_DGRAM, SOCK_RAW),
+                                 Values(0, 1, 255, ETH_P_IP, ETH_P_IPV6,
+                                        std::numeric_limits<uint16_t>::max())));
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor

test/util/capability_util.h

@@ -17,6 +17,8 @@
 #ifndef GVISOR_TEST_UTIL_CAPABILITY_UTIL_H_
 #define GVISOR_TEST_UTIL_CAPABILITY_UTIL_H_
 
+#include "test/util/posix_error.h"
+
 #if defined(__Fuchsia__)
 // Nothing to include.
 #elif defined(__linux__)