Add support for SO_REUSEADDR to UDP sockets/endpoints.

On UDP sockets, SO_REUSEADDR allows multiple sockets to bind to the same
address, but only delivers packets to the most recently bound socket. This
differs from the behavior of SO_REUSEADDR on TCP sockets. SO_REUSEADDR for TCP
sockets will likely need an almost completely independent implementation.

SO_REUSEADDR has some odd interactions with the similar SO_REUSEPORT. These
interactions are tested fairly extensively and all but one particularly odd
one (that honestly seems like a bug) behave the same on gVisor and Linux.

PiperOrigin-RevId: 315844832

5 files changed, 72 insertions, 51 deletions

diff --git a/test/syscalls/linux/socket_bind_to_device_sequence.cc b/test/syscalls/linux/socket_bind_to_device_sequence.cc
index 1967329ee..4b2cb0606 100644
--- a/test/syscalls/linux/socket_bind_to_device_sequence.cc
+++ b/test/syscalls/linux/socket_bind_to_device_sequence.cc
@@ -363,8 +363,9 @@ TEST_P(BindToDeviceSequenceTest, BindTwiceWithReuseOnce) {
 }
 
 TEST_P(BindToDeviceSequenceTest, BindWithReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
+  // FIXME(b/158253835): Support SO_REUSEADDR on TCP sockets.
+  SKIP_IF(IsRunningOnGvisor() &&
+          (GetParam().type & SOCK_STREAM) == SOCK_STREAM);
 
   ASSERT_NO_FATAL_FAILURE(
       BindSocket(/* reusePort */ false, /* reuse_addr */ true));
@@ -405,8 +406,9 @@ TEST_P(BindToDeviceSequenceTest, BindReuseAddrReusePortThenReusePort) {
 }
 
 TEST_P(BindToDeviceSequenceTest, BindReuseAddrReusePortThenReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
+  // FIXME(b/158253835): Support SO_REUSEADDR on TCP sockets.
+  SKIP_IF(IsRunningOnGvisor() &&
+          (GetParam().type & SOCK_STREAM) == SOCK_STREAM);
 
   ASSERT_NO_FATAL_FAILURE(BindSocket(/* reuse_port */ true,
                                      /* reuse_addr */ true,
@@ -434,8 +436,9 @@ TEST_P(BindToDeviceSequenceTest, BindDoubleReuseAddrReusePortThenReusePort) {
 }
 
 TEST_P(BindToDeviceSequenceTest, BindDoubleReuseAddrReusePortThenReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
+  // FIXME(b/158253835): Support SO_REUSEADDR on TCP sockets.
+  SKIP_IF(IsRunningOnGvisor() &&
+          (GetParam().type & SOCK_STREAM) == SOCK_STREAM);
 
   ASSERT_NO_FATAL_FAILURE(BindSocket(
       /* reuse_port */ true, /* reuse_addr */ true, /* bind_to_device */ 0));
@@ -469,10 +472,20 @@ TEST_P(BindToDeviceSequenceTest, BindReuseAddrThenReuseAddr) {
                                      /* bind_to_device */ 0, EADDRINUSE));
 }
 
-// This behavior seems like a bug?
 TEST_P(BindToDeviceSequenceTest,
        BindReuseAddrThenReuseAddrReusePortThenReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
+  // The behavior described in this test seems like a Linux bug. It doesn't
+  // make any sense and it is unlikely that any applications rely on it.
+  //
+  // Both SO_REUSEADDR and SO_REUSEPORT allow binding multiple UDP sockets to
+  // the same address and deliver each packet to exactly one of the bound
+  // sockets. If both are enabled, one of the strategies is selected to route
+  // packets. The strategy is selected dynamically based on the settings of the
+  // currently bound sockets. Usually, the strategy is selected based on the
+  // common setting (SO_REUSEADDR or SO_REUSEPORT) amongst the sockets, but for
+  // some reason, Linux allows binding sets of sockets with no overlapping
+  // settings in some situations. In this case, it is not obvious which strategy
+  // would be selected as the configured setting is a contradiction.
   SKIP_IF(IsRunningOnGvisor());
 
   ASSERT_NO_FATAL_FAILURE(BindSocket(
diff --git a/test/syscalls/linux/socket_inet_loopback.cc b/test/syscalls/linux/socket_inet_loopback.cc
index fa890ec98..a914d9a12 100644
--- a/test/syscalls/linux/socket_inet_loopback.cc
+++ b/test/syscalls/linux/socket_inet_loopback.cc
@@ -1900,9 +1900,6 @@ TEST_P(SocketMultiProtocolInetLoopbackTest, V6EphemeralPortReserved) {
 TEST_P(SocketMultiProtocolInetLoopbackTest, V6EphemeralPortReservedReuseAddr) {
   auto const& param = GetParam();
 
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor() && param.type == SOCK_DGRAM);
-
   // Bind the v6 loopback on a dual stack socket.
   TestAddress const& test_addr = V6Loopback();
   sockaddr_storage bound_addr = test_addr.addr;
@@ -2091,9 +2088,6 @@ TEST_P(SocketMultiProtocolInetLoopbackTest,
        V4MappedEphemeralPortReservedResueAddr) {
   auto const& param = GetParam();
 
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor() && param.type == SOCK_DGRAM);
-
   // Bind the v4 loopback on a dual stack socket.
   TestAddress const& test_addr = V4MappedLoopback();
   sockaddr_storage bound_addr = test_addr.addr;
@@ -2283,9 +2277,6 @@ TEST_P(SocketMultiProtocolInetLoopbackTest, V4EphemeralPortReserved) {
 TEST_P(SocketMultiProtocolInetLoopbackTest, V4EphemeralPortReservedReuseAddr) {
   auto const& param = GetParam();
 
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor() && param.type == SOCK_DGRAM);
-
   // Bind the v4 loopback on a v4 socket.
   TestAddress const& test_addr = V4Loopback();
   sockaddr_storage bound_addr = test_addr.addr;
diff --git a/test/syscalls/linux/socket_ip_udp_generic.cc b/test/syscalls/linux/socket_ip_udp_generic.cc
index 1c533fdf2..edb86aded 100644
--- a/test/syscalls/linux/socket_ip_udp_generic.cc
+++ b/test/syscalls/linux/socket_ip_udp_generic.cc
@@ -225,9 +225,6 @@ TEST_P(UDPSocketPairTest, ReuseAddrDefault) {
 TEST_P(UDPSocketPairTest, SetReuseAddr) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
 
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   ASSERT_THAT(setsockopt(sockets->first_fd(), SOL_SOCKET, SO_REUSEADDR,
                          &kSockOptOn, sizeof(kSockOptOn)),
               SyscallSucceeds());
@@ -292,9 +289,6 @@ TEST_P(UDPSocketPairTest, SetReusePort) {
 TEST_P(UDPSocketPairTest, SetReuseAddrReusePort) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
 
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   ASSERT_THAT(setsockopt(sockets->first_fd(), SOL_SOCKET, SO_REUSEADDR,
                          &kSockOptOn, sizeof(kSockOptOn)),
               SyscallSucceeds());
diff --git a/test/syscalls/linux/socket_ip_unbound.cc b/test/syscalls/linux/socket_ip_unbound.cc
index af8dda19c..5536ab53a 100644
--- a/test/syscalls/linux/socket_ip_unbound.cc
+++ b/test/syscalls/linux/socket_ip_unbound.cc
@@ -157,7 +157,7 @@ TEST_P(IPUnboundSocketTest, TOSDefault) {
   int get = -1;
   socklen_t get_sz = sizeof(get);
   constexpr int kDefaultTOS = 0;
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, kDefaultTOS);
@@ -173,7 +173,7 @@ TEST_P(IPUnboundSocketTest, SetTOS) {
 
   int get = -1;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, set);
@@ -188,7 +188,7 @@ TEST_P(IPUnboundSocketTest, ZeroTOS) {
               SyscallSucceedsWithValue(0));
   int get = -1;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, set);
@@ -210,7 +210,7 @@ TEST_P(IPUnboundSocketTest, InvalidLargeTOS) {
   }
   int get = -1;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, kDefaultTOS);
@@ -229,7 +229,7 @@ TEST_P(IPUnboundSocketTest, CheckSkipECN) {
   }
   int get = -1;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, expect);
@@ -249,7 +249,7 @@ TEST_P(IPUnboundSocketTest, ZeroTOSOptionSize) {
   }
   int get = -1;
   socklen_t get_sz = 0;
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, 0);
   EXPECT_EQ(get, -1);
@@ -276,7 +276,7 @@ TEST_P(IPUnboundSocketTest, SmallTOSOptionSize) {
     }
     uint get = -1;
     socklen_t get_sz = i;
-    EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+    ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
                 SyscallSucceedsWithValue(0));
     EXPECT_EQ(get_sz, expect_sz);
     // Account for partial copies by getsockopt, retrieve the lower
@@ -297,7 +297,7 @@ TEST_P(IPUnboundSocketTest, LargeTOSOptionSize) {
     // We expect the system call handler to only copy atmost sizeof(int) bytes
     // as asserted by the check below. Hence, we do not expect the copy to
     // overflow in getsockopt.
-    EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+    ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
                 SyscallSucceedsWithValue(0));
     EXPECT_EQ(get_sz, sizeof(int));
     EXPECT_EQ(get, set);
@@ -325,7 +325,7 @@ TEST_P(IPUnboundSocketTest, NegativeTOS) {
   }
   int get = -1;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, expect);
@@ -338,20 +338,20 @@ TEST_P(IPUnboundSocketTest, InvalidNegativeTOS) {
   TOSOption t = GetTOSOption(GetParam().domain);
   int expect;
   if (GetParam().domain == AF_INET) {
-    EXPECT_THAT(setsockopt(socket->get(), t.level, t.option, &set, set_sz),
+    ASSERT_THAT(setsockopt(socket->get(), t.level, t.option, &set, set_sz),
                 SyscallSucceedsWithValue(0));
     expect = static_cast<uint8_t>(set);
     if (GetParam().protocol == IPPROTO_TCP) {
       expect &= ~INET_ECN_MASK;
     }
   } else {
-    EXPECT_THAT(setsockopt(socket->get(), t.level, t.option, &set, set_sz),
+    ASSERT_THAT(setsockopt(socket->get(), t.level, t.option, &set, set_sz),
                 SyscallFailsWithErrno(EINVAL));
     expect = 0;
   }
   int get = 0;
   socklen_t get_sz = sizeof(get);
-  EXPECT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
+  ASSERT_THAT(getsockopt(socket->get(), t.level, t.option, &get, &get_sz),
               SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_sz, sizeof(get));
   EXPECT_EQ(get, expect);
@@ -422,6 +422,38 @@ TEST_P(IPUnboundSocketTest, InsufficientBufferTOS) {
   EXPECT_THAT(sendmsg(socket->get(), &msg, 0), SyscallFailsWithErrno(EINVAL));
 }
 
+TEST_P(IPUnboundSocketTest, ReuseAddrDefault) {
+  auto socket = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
+
+  // FIXME(b/76031995): gVisor TCP sockets default to SO_REUSEADDR enabled.
+  SKIP_IF(IsRunningOnGvisor() &&
+          (GetParam().type & SOCK_STREAM) == SOCK_STREAM);
+
+  int get = -1;
+  socklen_t get_sz = sizeof(get);
+  ASSERT_THAT(
+      getsockopt(socket->get(), SOL_SOCKET, SO_REUSEADDR, &get, &get_sz),
+      SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get, kSockOptOff);
+  EXPECT_EQ(get_sz, sizeof(get));
+}
+
+TEST_P(IPUnboundSocketTest, SetReuseAddr) {
+  auto socket = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
+
+  ASSERT_THAT(setsockopt(socket->get(), SOL_SOCKET, SO_REUSEADDR, &kSockOptOn,
+                         sizeof(kSockOptOn)),
+              SyscallSucceedsWithValue(0));
+
+  int get = -1;
+  socklen_t get_sz = sizeof(get);
+  ASSERT_THAT(
+      getsockopt(socket->get(), SOL_SOCKET, SO_REUSEADDR, &get, &get_sz),
+      SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get, kSockOptOn);
+  EXPECT_EQ(get_sz, sizeof(get));
+}
+
 INSTANTIATE_TEST_SUITE_P(
     IPUnboundSockets, IPUnboundSocketTest,
     ::testing::ValuesIn(VecCat<SocketKind>(VecCat<SocketKind>(
diff --git a/test/syscalls/linux/socket_ipv4_udp_unbound.cc b/test/syscalls/linux/socket_ipv4_udp_unbound.cc
index 1294d9050..4db9553e1 100644
--- a/test/syscalls/linux/socket_ipv4_udp_unbound.cc
+++ b/test/syscalls/linux/socket_ipv4_udp_unbound.cc
@@ -1672,10 +1672,10 @@ TEST_P(IPv4UDPUnboundSocketTest, TestBindToBcastThenSend) {
 }
 
 // Check that SO_REUSEADDR always delivers to the most recently bound socket.
-TEST_P(IPv4UDPUnboundSocketTest, ReuseAddrDistribution) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
+//
+// FIXME(gvisor.dev/issue/873): Endpoint order is not restored correctly. Enable
+// random and co-op save (below) once that is fixed.
+TEST_P(IPv4UDPUnboundSocketTest, ReuseAddrDistribution_NoRandomSave) {
   std::vector<std::unique_ptr<FileDescriptor>> sockets;
   sockets.emplace_back(ASSERT_NO_ERRNO_AND_VALUE(NewSocket()));
 
@@ -1696,6 +1696,9 @@ TEST_P(IPv4UDPUnboundSocketTest, ReuseAddrDistribution) {
 
   constexpr int kMessageSize = 200;
 
+  // FIXME(gvisor.dev/issue/873): Endpoint order is not restored correctly.
+  const DisableSave ds;
+
   for (int i = 0; i < 10; i++) {
     // Add a new receiver.
     sockets.emplace_back(ASSERT_NO_ERRNO_AND_VALUE(NewSocket()));
@@ -1836,9 +1839,6 @@ TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConvertibleToReusePort) {
 }
 
 TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConvertibleToReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   auto socket1 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket2 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket3 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
@@ -1880,9 +1880,6 @@ TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConvertibleToReuseAddr) {
 }
 
 TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConversionReversable1) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   auto socket1 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket2 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket3 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
@@ -1927,9 +1924,6 @@ TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConversionReversable1) {
 }
 
 TEST_P(IPv4UDPUnboundSocketTest, BindReuseAddrReusePortConversionReversable2) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   auto socket1 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket2 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket3 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
@@ -2020,9 +2014,6 @@ TEST_P(IPv4UDPUnboundSocketTest, BindDoubleReuseAddrReusePortThenReusePort) {
 }
 
 TEST_P(IPv4UDPUnboundSocketTest, BindDoubleReuseAddrReusePortThenReuseAddr) {
-  // FIXME(b/129164367): Support SO_REUSEADDR on UDP sockets.
-  SKIP_IF(IsRunningOnGvisor());
-
   auto socket1 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket2 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());
   auto socket3 = ASSERT_NO_ERRNO_AND_VALUE(NewSocket());