NAS 5GS refactor
The goal of this MR is to reorganize the NR NAS code into:
- enc/dec library functions (5GS, 5GMM, 5GSM, NR_NAS_defs.h,
nr_fgs_nas_lib.c)
- handlers and callbacks (nr_nas_msg.c)
The following changes are introduced:
1. migrate 5GS enc/dec lib (5GMM and 5GSM) to a dedicated folder
2. add a nested CMakeLists structure
3. refactor NR NAS enc/dec functions
4. refactor NR NAS messages struct definitions
5. remove most of dependency from NAS LTE
6. further refactor of PDU Session Establishment Accept processing to
separate enc/dec from handling
7. made naming of 5GS definitions consistent whenever necessary
8. cleanup unused code
9. remove redundant struct definitions
Also:
1. fix decoding of AMF Set ID in 5G-S-TMSI UE identity
2. replace Byte_t directly with uint8_t
This commit is introducing the following macro changes:
(1) Migrate NAS 5GS lib files to a new 5GS subfolder in NR_UE
and organize NAS 5GS lib messages into 5GMM and 5GSM subfolders.
A nested CMake structure was implemented and CMakeLists.txt were
added whenever necessary. This is effectively separating 5GS
libraries from LTE libraries.
(2) In order to simplify the separation of 5GS libs from LTE libs,
remaining dependencies from NAS LTE (e.g. nas_ue_task.c, ue-idx-standalone)
were removed in the process
(3) ExtendedProtocolDiscriminator.c/.h and SpareHalfOctet.c/.h were deleted
and affected types were replaced with simple integer types
(4) Cleanup: unused definitions and libs (e.g. LIB_5GNAS_GNB)
were removed
(5) Update doc/Doxyfile
(6) clang-formatted the migrated files in the process
(7) Update includes of headers in affected files
Handle IPv6 (and IPv4v6) PDU sessions by correctly instructing
nas_config() to set up the interface with provided IP addresses.
Note that as of now, IPv6 PDU sessions have not been fully tested.
Remove a useless assert at the gNB; to my understanding the gNB does not
care about the IP session type (at least for IP), as it just
transparently tunnels the IP packets from/to GTP.
I added a comment in the code where to change to request a PDU session
different from IPv4. Currently it is hardcoded to IPv4, and it seems
that a default OAI 5GC config would reject a PDU session type different
from IPv4.
These rules & route are necessary to properly send packets on oaitun_ue1
interface:
1. This forces the packets coming from a subnet different than the UE's
subnet to go back through oaitun_ue1 rather than via what the default
route defined on the system (e.g., important if ping from the
internet arrives).
2. On machines setting net.ipv4.conf.oaitun_ue1.rp_filter=1 (e.g.
RHEL), this prevents that source filtering for packets coming back is
applied and those packets be dropped. By default, many hosts have
rp_filter=2, so no strict source filtering is applied, and it would
work; on others, this rule prevents source filter dropping.
Prior to this commit, there was a global variable baseNetAddress that
could be set independently through a setter and also through the
configuration module. This baseNetAddress (16 bits IPv4) would then be
complemented with two more bytes in nas_config().
However, this is counter-productive, as not only we have a global
variable that is avoidable (we can give the entire address to
nas_config() directly), but it also would not work with IPv6. Hence,
modify to give nas_config() the entire address. A follow-up commit will
add IPv6 support.
Before this commit each time the message was captured, it entered the
default switch statement, which is meant to show that we received an
uknown IEI.
Now after the DNN IEI, we set offset=msg_length, to exit the
switch.
Robert Schmidt