[CSI] Do not allow stage_publish_base_dir to be a sub-directory of mount_dir

[ggriffiths]

Nomad version

Any nomad version 1.3.0 or greater

Operating system and Environment details

Any OS

Issue

If a CSI plugin uses mount_dir = /var/lib/test and stage_publish_base_dir = /var/lib/test/publish, then this line will cause all mount points and underlying data to be at risk:
https://github.com/hashicorp/nomad/blob/v1.3.0/client/allocrunner/taskrunner/plugin_supervisor_hook.go#L427-L430

Reproduction steps

Use mount_dir = /var/lib/test and stage_publish_base_dir = /var/lib/test/publish for any CSI driver, and the mount point will not resolve properly and data could be at risk on CSI Plugin restart.

Expected Result

CSI Plugin Stanza validation should fail if stage_publish_base_dir is inside of mount_dir

Actual Result

CSI plugin stanza validation succeeds

Job file (if appropriate)

n/a - CSI plugin and job configuration

Nomad Server logs (if appropriate)

n/a

Nomad Client logs (if appropriate)

n/a

[tgross]

Hi @ggriffiths! This makes sense to me. I've reviewed your PR and made some comments.

[tgross]

#19441 has been merged and will ship in Nomad 1.7.2 (plus backports to 1.6 and 1.5)

[ggriffiths]

Thank you @tgross !

[github-actions]

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