Update RX sequence number after refusing TCP FIN packet.

source/FreeRTOS_TCP_State_Handling.c

@@ -584,6 +584,8 @@
             {
                 /* Peer is requesting to stop, see if we're really finished. */
                 xMayClose = pdTRUE;
+                ulIntermediateResult = ulSequenceNumber + ulReceiveLength - pxTCPWindow->rx.ulCurrentSequenceNumber;
+                lDistance = ( int32_t ) ulIntermediateResult;
 
                 /* Checks are only necessary if we haven't sent a FIN yet. */
                 if( pxSocket->u.xTCP.bits.bFinSent == pdFALSE_UNSIGNED )
@@ -601,22 +603,28 @@
                                                  ( int ) bRxComplete,
                                                  ( int ) bTxDone ) );
                         xMayClose = pdFALSE;
-                    }
-                    else
-                    {
-                        ulIntermediateResult = ulSequenceNumber + ulReceiveLength - pxTCPWindow->rx.ulCurrentSequenceNumber;
-                        lDistance = ( int32_t ) ulIntermediateResult;
 
-                        if( lDistance > 1 )
+                        /* This action is necessary to ensure proper handling of any subsequent packets that
+                         * may arrive after the refused FIN packet. Note that we only update it when the sequence
+                         * of FIN packet is correct. Otherwise, we wait for re-transmission. */
+                        if( lDistance <= 1 )
                         {
-                            FreeRTOS_debug_printf( ( "Refusing FIN: Rx not complete %d (cur %u high %u)\n",
-                                                     ( int ) lDistance,
-                                                     ( unsigned ) ( pxTCPWindow->rx.ulCurrentSequenceNumber - pxTCPWindow->rx.ulFirstSequenceNumber ),
-                                                     ( unsigned ) ( pxTCPWindow->rx.ulHighestSequenceNumber - pxTCPWindow->rx.ulFirstSequenceNumber ) ) );
-
-                            xMayClose = pdFALSE;
+                            pxTCPWindow->rx.ulCurrentSequenceNumber = pxTCPWindow->rx.ulFINSequenceNumber + 1U;
                         }
                     }
+                    else if( lDistance > 1 )
+                    {
+                        FreeRTOS_debug_printf( ( "Refusing FIN: Rx not complete %d (cur %u high %u)\n",
+                                                 ( int ) lDistance,
+                                                 ( unsigned ) ( pxTCPWindow->rx.ulCurrentSequenceNumber - pxTCPWindow->rx.ulFirstSequenceNumber ),
+                                                 ( unsigned ) ( pxTCPWindow->rx.ulHighestSequenceNumber - pxTCPWindow->rx.ulFirstSequenceNumber ) ) );
+
+                        xMayClose = pdFALSE;
+                    }
+                    else
+                    {
+                        /* Empty else marker. */
+                    }
                 }
 
                 if( xTCPWindowLoggingLevel > 0 )

test/Coverity/README.md

@@ -1,6 +1,6 @@
 # Static code analysis for FreeRTOS-Plus-TCP library
 This directory is made for the purpose of statically testing the MISRA C:2012 compliance of FreeRTOS+TCP using
-[Synopsys Coverity](https://www.synopsys.com/software-integrity/security-testing/static-analysis-sast.html) static analysis tool.
+[Synopsys Coverity](https://www.blackduck.com/static-analysis-tools-sast/coverity.html) static analysis tool.
 To that end, this directory provides a [CMake](https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/test/Coverity/CMakeLists.txt)
 file and [configuration files](https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/tree/main/test/Coverity/ConfigFiles) required to build
 an application for the tool to analyze.

test/unit-test/FreeRTOS_TCP_State_Handling/FreeRTOS_TCP_State_Handling_utest.c

@@ -821,6 +821,47 @@ void test_prvHandleEstablished_FINNotSentRXComplete( void )
     TEST_ASSERT_EQUAL( 40, xSendLength );
 }
 
+/**
+ * @brief Data left for receiving when receiving TCP packet with FIN/ACK.
+ */
+void test_prvHandleEstablished_FINNotSentRXNotCompleteNotExpectedSeq( void )
+{
+    BaseType_t xSendLength = 0;
+
+    pxSocket = &xSocket;
+
+    pxNetworkBuffer = &xNetworkBuffer;
+    pxNetworkBuffer->pucEthernetBuffer = ucEthernetBuffer;
+
+    /* Map the buffer onto the ProtocolHeader_t struct for easy access to the fields. */
+    ProtocolHeaders_t * pxProtocolHeaders = ( ( ProtocolHeaders_t * )
+                                              &( pxNetworkBuffer->pucEthernetBuffer[ ipSIZE_OF_ETH_HEADER + ipSIZE_OF_IPv4_HEADER ] ) );
+    TCPHeader_t * pxTCPHeader = &pxProtocolHeaders->xTCPHeader;
+    TCPWindow_t * pxTCPWindow = &pxSocket->u.xTCP.xTCPWindow;
+
+    ulCalled = 0;
+    pxTCPHeader->ucTCPFlags = tcpTCP_FLAG_FIN | tcpTCP_FLAG_ACK;
+    pxTCPHeader->ulSequenceNumber = FreeRTOS_htonl( 1502 );
+    pxTCPHeader->usWindow = 1000;
+    pxSocket->u.xTCP.txStream = ( StreamBuffer_t * ) 0x12345678;
+    pxSocket->u.xTCP.pxHandleSent = NULL;
+    pxSocket->u.xTCP.bits.bFinSent = pdFALSE;
+    pxTCPWindow->rx.ulCurrentSequenceNumber = 1500;
+
+    uxIPHeaderSizeSocket_IgnoreAndReturn( ipSIZE_OF_IPv4_HEADER );
+    ulTCPWindowTxAck_ExpectAnyArgsAndReturn( 0 );
+    prvTCPAddTxData_ExpectAnyArgs();
+    xTCPWindowRxEmpty_ExpectAnyArgsAndReturn( pdFALSE );
+    xTCPWindowTxDone_ExpectAnyArgsAndReturn( pdTRUE );
+    prvTCPPrepareSend_ExpectAnyArgsAndReturn( 0 );
+
+    xSendLength = prvHandleEstablished( pxSocket,
+                                        &pxNetworkBuffer,
+                                        0,
+                                        0 );
+    TEST_ASSERT_EQUAL( 0, xSendLength );
+}
+
 /**
  * @brief Data left for receiving when receiving TCP packet with FIN/ACK.
  */
@@ -846,7 +887,7 @@ void test_prvHandleEstablished_FINNotSentRXNotComplete( void )
     pxSocket->u.xTCP.txStream = ( StreamBuffer_t * ) 0x12345678;
     pxSocket->u.xTCP.pxHandleSent = NULL;
     pxSocket->u.xTCP.bits.bFinSent = pdFALSE;
-    pxTCPWindow->rx.ulCurrentSequenceNumber = 2501;
+    pxTCPWindow->rx.ulCurrentSequenceNumber = 1500;
 
     uxIPHeaderSizeSocket_IgnoreAndReturn( ipSIZE_OF_IPv4_HEADER );
     ulTCPWindowTxAck_ExpectAnyArgsAndReturn( 0 );