PVF: potential "could not create a temporary directory" error

[mrcnski]

It is possible to run into this warning. It is caused by us doing security checks in the PVF cache directory (/tmp/.tmpIcLriO in the warning) before creating this cache directory.

WARN parachain::pvf: 🚨 Some security issues have been detected. 
Running validation of malicious PVF code has a higher risk of compromising this machine.
  - Optional: Cannot unshare user namespace and change root, which are Linux-specific kernel security features: could not create a temporary directory in "/tmp/.tmpIcLriO": No such file or directory (os error 2) at path "/tmp/.tmpIcLriO/check-can-unshare-4XnFgA"

Severity: annoyance

This should only occur if the PVF cache path (/tmp/.tmpIcLriO above) doesn't exist, i.e. the node is running for the first time.

On Linux 5.13+ it will be only a warning. On Linux 5.12- it's an error forcing shutdown of the node.

Mitigation: The validator will have to make sure the directory exists and restart the node.

This is a mild annoyance and should be mentioned in the release notes, but not worth a backport.

[infrachris]

1. I found that simply restarting the node resolves the 'no such file or directory' error.
2. My error message was slightly different than what was described. In my error, the first portion 'could not create temp directory in' references: '.../pvf-artifacts'

could not create a temporary directory in "/home/polkadot/.local/share/polkadot/chains/ksmcc3/db/full/pvf-artifacts": No such file or directory (os error 2) at path "/home/polkadot/.local/share/polkadot/chains/ksmcc3/db/full/pvf-artifacts/check-can-unshare-M7pL8f"

[mrcnski]

Good to hear. Thanks for letting us know @yayoi-k!