Proposal: bindmount init's procfs

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
20/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
go
Domain
operating-systems

Research direction

Start by tracing runc's handling of the initProcessTime check and the /run/runc/[ctr]/init path, then investigate how bind-mounted /proc/[pid] entries behave across PID namespaces. The issue does not name implementation files or tests; done would require choosing and validating a concrete approach for managing containers and detecting the init process without the existing magic.

Written by the indexing model from the issue text.

Description

So, I was playing around with different tricks you can do with persistent namespaces and I noticed that you can bindmount /proc/[pid] directories:

% mount --bind /proc/1 /tmp/init
% cat /tmp/init/stat
1 (systemd) S 0 1 1 0 -1 4210944 91669 332185088 31 11021 346 382 571372 98303 20 0 1 0 2 127012864 1248 18446744073709551615 1 1 0 0 0 0 671173123 4096 1260 0 0 0 17 0 0 0 581 0 0 0 0 0 0 0 0 0 0
% mount --bind /proc/self /tmp/self
% ls /tmp/self
ls: cannot open directory '/tmp/self': No such process

This means there are two things that we can solve with this:

  1. We can manage containers from a different PID namespace, because the /proc/self/stat pseudo-file will generate the correct PID for us. I'm not sure what happens if you try to access it from a different namespace though (probably ESRCH).

  2. We can remove the initProcessTime magic with a simple check to see if /run/runc/[ctr]/init gives us ESRCH. This is a fool-proof method because we're pinning the kernel struct task's procfs entry.

There's also some other cool stuff we could do.

Dominant language
Go
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