Setup cgroup.subtree_control controllers when necessary in cgroupsv2 #208
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ndrewh
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This commit adds extra setup when cgroupsv2 is enabled. In particular, we make sure that the root namespace has setup cgroup.subtree_control with the controllers we need. If the necessary controller are not listed, we have to move all processes out of the root namespace before we can change this (the 'no internal processes' rule: https://unix.stackexchange.com/a/713343). Currently we only handle the case where the nsjail process is the only process in the cgroup. It seems like this would be relatively rare, but since nsjail is frequently the root process in a Docker container (e.g. for hosting CTF challenges), I think this case is common enough to make it worth implementing. This also adds `--detect_cgroupv2`, which will attempt to detect whether `--cgroupv2_mount` is a valid cgroupv2 mount, and if so it will set `use_cgroupv2`. This is useful in containerized environments where you may not know the kernel version ahead of time. References: https://github.com/redpwn/jail/blob/master/internal/cgroup/cgroup2.go
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Thanks, I'll pull it. There're a couple of things which I might rework later - things like the style of comments, but it doesn't affect the logic of the PR, so let's do it. |
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This commit adds extra setup when cgroupsv2 is enabled. In particular, we make sure that the root cgroup (whatever
cgroupv2_mountis set to) has setup cgroup.subtree_control with the controllers we need.If the necessary controller are not listed, we have to move all processes out of the root cgroup before we can change this (the 'no internal processes' rule: https://unix.stackexchange.com/a/713343). Currently this handles the case where the nsjail process is the only process in the cgroup. It seems like this would be relatively rare, but since nsjail is frequently the root process in a Docker container (e.g. for hosting CTF challenges), I think this case is common enough to make it worth implementing.
This also adds
--detect_cgroupv2, which will attempt to detect whether--cgroupv2_mountis a valid cgroupv2 mount, and will setuse_cgroupv2accordingly. This is useful in containerized environments where you may not know the configuration ahead of time.References:
https://github.com/redpwn/jail/blob/master/internal/cgroup/cgroup2.go
See #196