AMF sends in-valid GUTI in registration accept

[ashithacdac]

Issue:
AMF sends an invalid GUTI in registration accept.

RCA:
During troubleshooting, it was observed that when the UE initiates a Registration Request with an invalid GUTI, the core attempts to fetch the AMF UE context using the received GUTI. Since the GUTI is invalid, the UE cannot be found in the core. As a result, the core creates a new AMF UE context and allocates a new valid GUTI for the UE.

However, during the handling of the Registration Request, when the IEs are decoded, the invalid GUTI received from the UE is set again to the UE context. This incorrectly replaces the valid GUTI that was newly assigned by the core. As a result, the core sends the invalid GUTI in the Registration Accept.

Fix:
Update GUTI only when GUAMI is valid.

Supporting Data:
Invalid-guti.zip

[Copilot]

Pull request overview

This PR addresses an issue where an invalid UE-provided 5G-GUTI could overwrite a newly allocated (valid) ue.Guti, causing the AMF to send an invalid GUTI in Registration Accept.

Changes:

• Only updates ue.Guti from the decoded Registration Request when the GUAMI derived from the UE’s GUTI matches the AMF’s served GUAMI.
• Adds a warning log when the received GUAMI does not match.

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[gab-arrobo]

@ashithacdac,
Thanks for your PR. Please rebase it and address Copilot's comments (if applicable)

[ashithacdac]

Changes have been incorporated, and the PR has been rebased.