Create the persisted session cache file with owner-only permissions

[gasbytes]

Description

On POSIX builds wolfssl_save_session_cache now opens the file with open in 0600 mode + fdopen.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[wolfSSL-Bot]

Can one of the admins verify this patch?

[Copilot]

Pull request overview

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This PR tightens permissions for persisted session cache files on POSIX builds by opening the cache file with owner-only permissions, and documents the security implications of writing session secrets to disk.

Changes:

• Added a POSIX-specific SaveSessionCacheOpen() helper that uses open(…, 0600) + fchmod() + fdopen().
• Switched wolfSSL_save_session_cache() to use SaveSessionCacheOpen() instead of XFOPEN().
• Added Doxygen warning about plaintext secrets and platform-specific file permissions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/ssl_sess.c	Adds POSIX open+chmod path to ensure the cache file is owner-only (0600).
doc/dox_comments/header_files/ssl.h	Documents plaintext secret risk and notes 0600 behavior on POSIX.

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[github-actions]

retest this please

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-openssl-compat
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m4-tls13
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753

[gasbytes]

Jenkins retest this please (lost logs)

[gasbytes]

Jenkins retest this please

[gasbytes]

Jenkins retest this please

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #11291

Scan targets checked: wolfcrypt-rs-bugs, wolfssl-bugs, wolfssl-src

Findings: 1
1 finding(s) posted as inline comments (see file-level comments below)

This review was generated automatically by Fenrir. Reported findings require changes before merge.

[philljj]

I think this looks good.

I would just suggest to use the wc_open_cloexec wrapper, and see if the fchmod can be refactored to a new or existing wrapper in wc_port.c

[gasbytes]

Jenkins retest this please (timeout)

[gasbytes]

Jenkins retest this please (lost logs)

[gasbytes]

Jenkins retest this please (timeout)

[gasbytes]

Jenkins retest this please (timeout)

[gasbytes]

Jenkins retest this please (timeout)

changes addressed