[riot-notifications] [RIOT-OS/RIOT] Add MUD URL option to DHCPv6 client (#15508)

Jan Romann notifications at github.com
Thu Nov 26 13:18:08 CET 2020

The RIOT community cares a lot about code quality.
Therefore, before describing what your contribution is about, we would like
you to make sure that your modifications are compliant with the RIOT
coding conventions, see https://github.com/RIOT-OS/RIOT/wiki/Coding-conventions.

### Contribution description

Put here the description of your contribution:
- describe which part(s) of RIOT is (are) involved
- if it's a bug fix, describe the bug that it solves and how it is solved
- you can also give more information to reviewers about how to test your changes

This contribution adds MUD (Manufacturer Usage Description) support to RIOTs DHCPv6-Client (as defined in [RFC 8520, section 10](https://tools.ietf.org/html/rfc8520#section-10)). If a MUD URL pointing to a MUD file is defined in the makefile, a MUD URL option is added to the DHCP packages sent by the client. This option contains the option code 112, the length of the URL, and the URL itself. 

This information can then be used by a MUD manager at the receiving end to retrieve a so called MUD file (using the MUD URL) and to extract information about the device's intended behavior, especially when it comes to communicating via the internet. Integrating MUD support into RIOT can enhance its capabilities for achieving a more secure Internet of Things.

### Testing procedure

Details steps to test your contribution:
- which test/example to compile for which board and is there a 'test' command
- how to know that it was not working/available in master
- the expected success test output

Using `scapy`, we added a test case under `tests/gnrc_dhcpv6_client_6lbr` that asserts a correct emission of a MUD URL as part of a DHCP option by checking for the corresponding option code (112), the specified `mudString` and the correct option length. The tests can be performed by executing the shell commands `make flash` (or `make all`), followed by `sudo make test` in the `tests/gnrc_dhcpv6_client_6lbr` directory. 

So far, `scapy` does not supported a direct check for the MUD URL option (hence the use of the generic `DHCP6OptUnknown` class) but we succesfully suggested its inclusion in `scapy`'s DHCP module in a [Pull Request](https://github.com/secdev/scapy/pull/2964). We will integrate the new class for the MUD option once a new version of scapy has been released. 

Furthermore, our changes can be tested manually by defining a MUD URL in the makefile under `tests/gnrc_dhcpv6_client_6lbr` or `tests/gnrc_dhcpv6_client/`, running `make all` and `make term`, and verifying the DHCP packages sent using software like Wireshark. When analyzing the packages sent in a network, RIOT devices should emit DHCP packages that contain the MUD option (see the screenshot below) when they are using the DHCP module and have a MUD URL defined.

![Example wireshark DHCP package analysis.](https://hackmd.informatik.uni-bremen.de/uploads/upload_e1e78fa9b24f6f6da4f73d45d4349954.png)

Before performing one of the tests described above, it is necessary to create a tap bridge by running 

sudo ./dist/tools/tapsetup/tapsetup

inside of RIOT's root directory.

### Issues/PRs references

To our knowledge, MUD or RFC 8520 in general have not been mentioned in any issues or pull requests so far.

Examples: Fixes #1234. See also #5678. Depends on PR #9876.

Please use keywords (e.g., fixes, resolve) with the links to the issues you
resolved, this way they will be automatically closed when your pull request
is merged. See https://help.github.com/articles/closing-issues-using-keywords/.
You can view, comment on, or merge this pull request online at:


-- Commit Summary --

  * net/dhcpv6: Add DHCPv6 option for MUD URL (RFC 8520)
  * tests/gnrc_dhcpv6_client_6lbr: Add MUD URL test

-- File Changes --

    M sys/include/net/dhcpv6.h (1)
    M sys/net/application_layer/dhcpv6/_dhcpv6.h (11)
    M sys/net/application_layer/dhcpv6/client.c (28)
    M tests/gnrc_dhcpv6_client_6lbr/Makefile (7)
    M tests/gnrc_dhcpv6_client_6lbr/tests/01-run.py (12)

-- Patch Links --


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