Return correct buffer size for ioctl(socket, FIONREAD)

Ioctl was returning just the buffer size from epsocket.endpoint
and it was not considering data from epsocket.SocketOperations
that was read from the endpoint, but not yet sent to the caller.

PiperOrigin-RevId: 266485461

pkg/sentry/socket/epsocket/epsocket.go

@@ -2104,7 +2104,8 @@ func (s *SocketOperations) Ioctl(ctx context.Context, _ *fs.File, io usermem.IO,
 	// SIOCGSTAMP is implemented by epsocket rather than all commonEndpoint
 	// sockets.
 	// TODO(b/78348848): Add a commonEndpoint method to support SIOCGSTAMP.
-	if int(args[1].Int()) == syscall.SIOCGSTAMP {
+	switch args[1].Int() {
+	case syscall.SIOCGSTAMP:
 		s.readMu.Lock()
 		defer s.readMu.Unlock()
 		if !s.timestampValid {
@@ -2116,6 +2117,25 @@ func (s *SocketOperations) Ioctl(ctx context.Context, _ *fs.File, io usermem.IO,
 			AddressSpaceActive: true,
 		})
 		return 0, err
+
+	case linux.TIOCINQ:
+		v, terr := s.Endpoint.GetSockOptInt(tcpip.ReceiveQueueSizeOption)
+		if terr != nil {
+			return 0, syserr.TranslateNetstackError(terr).ToError()
+		}
+
+		// Add bytes removed from the endpoint but not yet sent to the caller.
+		v += len(s.readView)
+
+		if v > math.MaxInt32 {
+			v = math.MaxInt32
+		}
+
+		// Copy result to user-space.
+		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(v), usermem.IOOpts{
+			AddressSpaceActive: true,
+		})
+		return 0, err
 	}
 
 	return Ioctl(ctx, s.Endpoint, io, args)

test/syscalls/linux/tcp_socket.cc

@@ -579,7 +579,7 @@ TEST_P(TcpSocketTest, TcpInq) {
     if (size == sizeof(buf)) {
       break;
     }
-    usleep(10000);
+    absl::SleepFor(absl::Milliseconds(10));
   }
 
   struct msghdr msg = {};
@@ -610,6 +610,25 @@ TEST_P(TcpSocketTest, TcpInq) {
   }
 }
 
+TEST_P(TcpSocketTest, Tiocinq) {
+  char buf[1024];
+  size_t size = sizeof(buf);
+  ASSERT_THAT(RetryEINTR(write)(s_, buf, size), SyscallSucceedsWithValue(size));
+
+  uint32_t seed = time(nullptr);
+  const size_t max_chunk = size / 10;
+  while (size > 0) {
+    size_t chunk = (rand_r(&seed) % max_chunk) + 1;
+    ssize_t read = RetryEINTR(recvfrom)(t_, buf, chunk, 0, nullptr, nullptr);
+    ASSERT_THAT(read, SyscallSucceeds());
+    size -= read;
+
+    int inq = 0;
+    ASSERT_THAT(ioctl(t_, TIOCINQ, &inq), SyscallSucceeds());
+    ASSERT_EQ(inq, size);
+  }
+}
+
 TEST_P(TcpSocketTest, TcpSCMPriority) {
   char buf[1024];
   ASSERT_THAT(RetryEINTR(write)(s_, buf, sizeof(buf)),