Allow reading IP_MULTICAST_LOOP and IP_MULTICAST_TTL on TCP sockets.

I am not really sure what the point of this is, but someone filed a bug about
it, so I assume something relies on it.

PiperOrigin-RevId: 316225127

2 files changed, 30 insertions, 0 deletions

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 6e4d607da..f225b00e7 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1855,6 +1855,9 @@ func (e *endpoint) GetSockOptBool(opt tcpip.SockOptBool) (bool, *tcpip.Error) {
 
 		return v, nil
 
+	case tcpip.MulticastLoopOption:
+		return true, nil
+
 	default:
 		return false, tcpip.ErrUnknownProtocolOption
 	}
@@ -1922,6 +1925,9 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 		e.UnlockUser()
 		return v, nil
 
+	case tcpip.MulticastTTLOption:
+		return 1, nil
+
 	default:
 		return -1, tcpip.ErrUnknownProtocolOption
 	}
diff --git a/test/syscalls/linux/socket_ip_tcp_generic.cc b/test/syscalls/linux/socket_ip_tcp_generic.cc
index 15adc8d0e..c2ecb639f 100644
--- a/test/syscalls/linux/socket_ip_tcp_generic.cc
+++ b/test/syscalls/linux/socket_ip_tcp_generic.cc
@@ -994,6 +994,30 @@ TEST_P(TCPSocketPairTest, SetTCPWindowClampBelowMinRcvBufConnectedSocket) {
   }
 }
 
+TEST_P(TCPSocketPairTest, IpMulticastTtlDefault) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  EXPECT_THAT(getsockopt(sockets->first_fd(), IPPROTO_IP, IP_MULTICAST_TTL,
+                         &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_GT(get, 0);
+}
+
+TEST_P(TCPSocketPairTest, IpMulticastLoopDefault) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  EXPECT_THAT(getsockopt(sockets->first_fd(), IPPROTO_IP, IP_MULTICAST_LOOP,
+                         &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_EQ(get, 1);
+}
+
 TEST_P(TCPSocketPairTest, TCPResetDuringClose_NoRandomSave) {
   DisableSave ds;  // Too many syscalls.
   constexpr int kThreadCount = 1000;