[16.0-stable] pillar/containerd: drop bogus scheduler from debug container exec

[christoph-zededa]

Description

Backport of #6231 to 16.0-stable.

The process spec used for execs into the debug container sets
Scheduler.Deadline, but leaves Scheduler.Policy empty. runc rejects that in
ToSchedAttr(), so the container init fails before it can execute the requested
program:

OCI runtime exec failed: exec failed: unable to start container process: invalid scheduler policy:: unknown

Both users of RunInDebugContainer() are affected on this branch:

• the collect-info run triggered through a local operator console (collectinfo
  agent) — the bug was reported from the field on 17.0.0-rc5, but this branch
  carries the same defect
• the bpftrace endpoint of pillar's http-debug interface

runc ignored process.scheduler on the exec path until v1.3.0-rc1
(opencontainers/runc#4585), so the bogus spec stayed unnoticed until the rootfs
moved from runc 1.1.12 to 1.3.3. This branch ships runc 1.3.3, so it is
affected.

Rather than completing the scheduler spec, this drops it. Scheduler.Deadline
is a SCHED_DEADLINE bandwidth parameter in nanoseconds, not a limit on how
long a process may run, and it was assigned a unix timestamp in seconds, so it
never did what it looks like it does — the kernel does not kill tasks for
missing a deadline either. The timeout that matters is enforced by
RunInDebugContainer() itself, which kills the process once its timer fires.
See #6231 for the full rationale.

Cherry-picked with git cherry-pick -x from
b7d446377a5a69712d9c1f57427961b9bdc042aa (the squash-merge of #6231 on
master). It applies cleanly and with no adaptation — the hunk in
pkg/pillar/containerd/run.go is identical on this branch.

How to test and validate this PR

Not covered by an automated test — the path needs a real containerd/runc, and
there is currently no unit or Eden coverage for execs into the debug container.

Reproduction of the bug (fails without this PR):

1. Configure a collect-info datastore of type HTTP/HTTPS with auth enabled on
   the local operator console.
2. Trigger collect info for the device.
3. Without this PR, pillar logs
   running [/usr/bin/collect-info.sh -u http://…] failed: process start failed: … invalid scheduler policy:: unknown
   and nothing is uploaded.
4. With this PR, collect-info.sh runs and its tarball appears on the
   datastore.

Please verify the tarball actually lands on the datastore rather than relying on
the pillar log line: RunInDebugContainer() reports failure whenever the script
writes anything to stderr (likely even on a successful run) and reports success
when the 15 min timeout kills the script, and collect-info.sh exits 0 even
when the upload itself fails. Those reporting bugs are pre-existing and out of
scope here.

A second, quicker check that exercises the same code path (no datastore
needed) — run a bpftrace script through pillar's http-debug interface:

# on the device
eve http-debug
# on the dev host - the debug server only listens on localhost, so tunnel it
ssh -p 2222 -L 6543:localhost:6543 root@127.1
bpftrace-compiler run-via-http 127.1:6543 examples/opensnoop.bt

Without this PR the response is
Error happened: process start failed: … invalid scheduler policy:: unknown;
with it the program runs and its JSON output is returned.

Note that bpftrace-compiler run-via-ssh does not exercise this path and
works either way: sshd runs inside the debug container itself, so the program
is started as a plain child of the ssh session, without an OCI exec at all.
Only run-via-http and run-via-edgeview POST to /debug/bpftrace and
therefore go through RunInDebugContainer().

Changelog notes

Fixed collect info triggered from a local operator console, and pillar's
bpftrace debug endpoint, which both failed to start with an
invalid scheduler policy error from the container runtime.

PR Backports

All four current LTS branches ship runc 1.3.3, so all of them are affected
(verified in #6231 by extracting /usr/bin/runc from the linuxkit/runc image
each branch pins). This PR is one of a set of four:

• 17.0-stable: [17.0-stable] pillar/containerd: drop bogus scheduler from debug container exec #6245
• 16.0-stable: this PR.
• 14.5-stable: [14.5-stable] pillar/containerd: drop bogus scheduler from debug container exec #6247
• 13.4-stable: [13.4-stable] pillar/containerd: drop bogus scheduler from debug container exec #6248 — adapted rather than a plain cherry-pick, that branch has
  neither containerd/run.go nor the collectinfo agent.

Checklist

• I've provided a proper description
• I've added the proper documentation — not needed, no user-facing behaviour
  or config surface changes
• I've tested my PR on amd64 device — not re-tested on this branch; the
  identical change was verified on amd64 in pillar/containerd: drop bogus scheduler from debug container exec #6231
• I've tested my PR on arm64 device
• I've written the test verification instructions
• I've set the proper labels to this PR

For backport PRs (remove it if it's not a backport):

• I've added a reference link to the original PR
• PR's title follows the template

And the last but not least:

• I've checked the boxes above, or I've provided a good reason why I didn't
  check them.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 23.55%. Comparing base (9f69150) to head (62a906b).
⚠️ Report is 138 commits behind head on 16.0-stable.

Additional details and impacted files

@@               Coverage Diff               @@
##           16.0-stable    #6246      +/-   ##
===============================================
+ Coverage        19.52%   23.55%   +4.02%     
===============================================
  Files               19       19              
  Lines             3021     2509     -512     
===============================================
+ Hits               590      591       +1     
+ Misses            2310     1787     -523     
- Partials           121      131      +10     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.