ulApplicationGetNextSequenceNumber undefined

Kernel
1

thomasnauw wrote on Tuesday, August 28, 2018:

I’m porting FreeRTOS V10.1.0 and FreeRTOS +TCP V2.0.7 to our STM32F217.
I’m now having an issue that doesn’t seem to be documented.
ulApplicationGetNextSequenceNumber, used in FreeRTOS_TCP_IP.c is undefined. It is defined in FreeRTOS_TCP_IP.c as an external function. The only info I can find is commented: “Generate a randomized TCP Initial Sequence Number per RFC.”
Problem seems to be the same in the examples.

Some help will be needed. Thank you.

Best regards
Thomas

2

rtel wrote on Tuesday, August 28, 2018:

The change improves security by enabling less predictability of sequence
numbers - abut apologies - it seems the update to the demo application
that demonstrated how to do this somehow got reverted and didn’t make it
into the release - the docs also need updating.

In the mean time, if you want a quick and dirty implementation of
ulApplicationGetNextSequenceNumber() you can ignore the input parameters
and just return a random number, thus:

/*
* Callback that provides the inputs necessary to generate a randomized TCP
* Initial Sequence Number per RFC 6528.  In this case just a psuedo random
* number is used so THIS IS NOT RECOMMENDED FOR PRODUCTION SYSTEMS.
*/
extern uint32_t ulApplicationGetNextSequenceNumber( uint32_t 
ulSourceAddress,
     uint16_t usSourcePort,
     uint32_t ulDestinationAddress,
     uint16_t usDestinationPort )
{
     ( void ) ulSourceAddress;
     ( void ) usSourcePort;
     ( void ) ulDestinationAddress;
     ( void ) usDestinationPort;

     return uxRand();
}

If you want a full implementation as per the RFC then have a look here,
although this implementation has dependencies on other libraries it
gives a reference:
https://github.com/aws/amazon-freertos/blob/master/lib/secure_sockets/portable/freertos_plus_tcp/aws_secure_sockets.c#L625

Also, if you are using a version of FreeRTOS prior to V10.1.0 you will
also need to set configENABLE_BACKWARD_COMPATIBILITY to 1 in
FreeRTOSConfig.h.

3

heinbali01 wrote on Tuesday, August 28, 2018:

Another remark, in addition to what Richard is writing: if you define your own version of uxRand(), please make sure that the seed gets a random value after each reboot.
You may use a randomiser peripheral in the CPU, or measure some analogue input, or the current time ( if you have ) to generate a random seed.