Explicitly bind endpoint to a NIC

Previously, any time a datagram-based network endpoint (e.g. UDP) was
bound, the bound NIC is always set based on the bound address (if
specified). However, we should only consider the endpoint bound to
an NIC if a NIC was explicitly bound to.

If an endpoint has been bound to an address and attempts to send packets
to an unconnected remote, the endpoint will default to sending packets
through the bound address' NIC if not explicitly bound to a NIC.

Updates #6565.

PiperOrigin-RevId: 396712415

1 files changed, 61 insertions, 0 deletions

diff --git a/test/syscalls/linux/udp_socket.cc b/test/syscalls/linux/udp_socket.cc
index d58b57c8b..b9af5cbdd 100644
--- a/test/syscalls/linux/udp_socket.cc
+++ b/test/syscalls/linux/udp_socket.cc
@@ -602,6 +602,67 @@ TEST_P(UdpSocketTest, DisconnectAfterBind) {
               SyscallFailsWithErrno(ENOTCONN));
 }
 
+void ConnectThenDisconnect(const FileDescriptor& sock,
+                           const sockaddr* bind_addr,
+                           const socklen_t expected_addrlen) {
+  // Connect the bound socket.
+  ASSERT_THAT(connect(sock.get(), bind_addr, expected_addrlen),
+              SyscallSucceeds());
+
+  // Disconnect.
+  {
+    sockaddr_storage unspec = {.ss_family = AF_UNSPEC};
+    ASSERT_THAT(connect(sock.get(), AsSockAddr(&unspec), sizeof(unspec)),
+                SyscallSucceeds());
+  }
+  {
+    // Check that we're not in a bound state.
+    sockaddr_storage addr;
+    socklen_t addrlen = sizeof(addr);
+    ASSERT_THAT(getsockname(sock.get(), AsSockAddr(&addr), &addrlen),
+                SyscallSucceeds());
+    ASSERT_EQ(addrlen, expected_addrlen);
+    // Everything should be the zero value except the address family.
+    sockaddr_storage expected = {
+        .ss_family = bind_addr->sa_family,
+    };
+    EXPECT_EQ(memcmp(&expected, &addr, expected_addrlen), 0);
+  }
+
+  {
+    // We are not connected so we have no peer.
+    sockaddr_storage addr;
+    socklen_t addrlen = sizeof(addr);
+    EXPECT_THAT(getpeername(sock.get(), AsSockAddr(&addr), &addrlen),
+                SyscallFailsWithErrno(ENOTCONN));
+  }
+}
+
+TEST_P(UdpSocketTest, DisconnectAfterBindToUnspecAndConnect) {
+  ASSERT_NO_ERRNO(BindLoopback());
+
+  sockaddr_storage unspec = {.ss_family = AF_UNSPEC};
+  int bind_res = bind(sock_.get(), AsSockAddr(&unspec), sizeof(unspec));
+  if (IsRunningOnGvisor() && !IsRunningWithHostinet()) {
+    // TODO(https://gvisor.dev/issue/6575): Match Linux's behaviour.
+    ASSERT_THAT(bind_res, SyscallFailsWithErrno(EINVAL));
+  } else if (GetFamily() == AF_INET) {
+    // Linux allows this for undocumented compatibility reasons:
+    // https://github.com/torvalds/linux/commit/29c486df6a208432b370bd4be99ae1369ede28d8.
+    ASSERT_THAT(bind_res, SyscallSucceeds());
+  } else {
+    ASSERT_THAT(bind_res, SyscallFailsWithErrno(EAFNOSUPPORT));
+  }
+
+  ASSERT_NO_FATAL_FAILURE(ConnectThenDisconnect(sock_, bind_addr_, addrlen_));
+}
+
+TEST_P(UdpSocketTest, DisconnectAfterConnectWithoutBind) {
+  ASSERT_NO_ERRNO(BindLoopback());
+
+  ASSERT_NO_FATAL_FAILURE(ConnectThenDisconnect(sock_, bind_addr_, addrlen_));
+}
+
 TEST_P(UdpSocketTest, BindToAnyConnnectToLocalhost) {
   ASSERT_NO_ERRNO(BindAny());