This PR fixes the non-root macOS use case where artifact downloads
stopped working. It seems setting a Credential on a SysProcAttr
used by the exec package will always cause fork/exec to fail -
even if the credential contains our own UID/GID or nil UID/GID.
Technically we do not need to set this as the child process will
inherit the parent UID/GID anyway... and not setting it makes
things work again ... /shrug
This PR fixes the artifact sandbox (new in Nomad 1.5) to allow downloading
artifacts into the shared 'alloc' directory made available to each task in
a common allocation. Previously we assumed the 'alloc' dir would be mounted
under the 'task' dir, but this is only the case in fs isolation: chroot; in
other modes the alloc dir is elsewhere.
* artifact: enable inheriting environment variables from client
This PR adds client configuration for specifying environment variables that
should be inherited by the artifact sandbox process from the Nomad Client agent.
Most users should not need to set these values but the configuration is provided
to ensure backwards compatability. Configuration of go-getter should ideally be
done through the artifact block in a jobspec task.
e.g.
```hcl
client {
artifact {
set_environment_variables = "TMPDIR,GIT_SSH_OPTS"
}
}
```
Closes#15498
* website: update set_environment_variables text to mention PATH
* client: sandbox go-getter subprocess with landlock
This PR re-implements the getter package for artifact downloads as a subprocess.
Key changes include
On all platforms, run getter as a child process of the Nomad agent.
On Linux platforms running as root, run the child process as the nobody user.
On supporting Linux kernels, uses landlock for filesystem isolation (via go-landlock).
On all platforms, restrict environment variables of the child process to a static set.
notably TMP/TEMP now points within the allocation's task directory
kernel.landlock attribute is fingerprinted (version number or unavailable)
These changes make Nomad client more resilient against a faulty go-getter implementation that may panic, and more secure against bad actors attempting to use artifact downloads as a privilege escalation vector.
Adds new e2e/artifact suite for ensuring artifact downloading works.
TODO: Windows git test (need to modify the image, etc... followup PR)
* landlock: fixup items from cr
* cr: fixup tests and go.mod file
