Set psk to NULL in ssl_psk_remove

[lhuang04]

Summary: set the psk to NULL after it is released. ssl_remove_psk will freessl->handshake->psk. If we don't set it to NULL. It may be used or free again in other conditions.

Test Plan:

Reviewers:

Subscribers: ronald.cron@arm.com

Tasks:

Tags:

Description

Address an issue that psk is not set to NULL after it is released.

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

• [x] changelog not required (robustness improvement)
• [x] 3.6 backport #9245
• [x] 2.28 backport #9246
• [x] tests not required (robustness improvement)

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[tom-cosgrove-arm]

Could you please raise backports against the mbedtls-2.28 and mbedtls-3.6 branches as well, please?

[lhuang04]

Backport PR 9245 for 3.6 branch, and PR 9246 for 2.8 branch.