Kir Kolyshkin
46a1510025
Seccomp's SCMP_ACT_KILL is SECCOMP_RET_KILL_THREAD: it kills the thread
that performed the syscall, not the whole thread group. As "runc init"
locks its main goroutine to the thread group leader, killing that thread
leaves a zombie leader whose remaining Go runtime threads are alive,
keeping the shared descriptor table -- and thus the child ends of the
sync socket and of the exec fifo -- open. The parent therefore never sees
an EOF, and since the thread group is not dead, neither wait(2) nor a
pidfd report anything either, so the parent waits forever.
Add waitForInitWrite, which polls the descriptor with a timeout and, when
nothing arrives, consults /proc/[pid]/stat -- the only thing that reports
a zombie thread group leader. Use it both for reading the sync socket and
for waiting on the exec fifo; the latter replaces the pidfd fast path,
which can not detect this case at all.
Kill and reap the leftover threads once a dead init is detected while
waiting for the exec fifo. They keep the container's stdio descriptors
open, so whoever inherited those would wait for an EOF just as long, and
they keep its cgroup populated, so destroying the container would fail.
Make nonChildProcess.terminate send SIGKILL rather than fail, so that
killDeadInit can use terminate for any init, be it our child ("runc
run") or not ("runc start"). In the latter case, init is only killed,
as reaping it is up to its parent.
Finally, do not wait(2) for the child in the setnsProcess.start error
path: a half-dead child is never reaped, and the deferred error handler
terminates and reaps it anyway.
Fixes #5087
Assisted-by: Claude Opus 5
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
libcontainer
Libcontainer provides a native Go implementation for creating containers with namespaces, cgroups, capabilities, and filesystem access controls. It allows you to manage the lifecycle of the container performing additional operations after the container is created.
Container
A container is a self contained execution environment that shares the kernel of the host system and which is (optionally) isolated from other containers in the system.
Using libcontainer
For a brief overview of using libcontainer, see example_test.go.
Container init
Because containers are spawned in a two step process you will need a binary that will be executed as the init process for the container. In libcontainer, we use the current binary (/proc/self/exe) to be executed as the init process, and use arg "init", we call the first step process "bootstrap", so you always need a "init" function as the entry of "bootstrap".
In addition to the go init function the early stage bootstrap is handled by importing nsenter.
For details on how runc implements such "init", see ../init.go and init_linux.go.
Checkpoint & Restore
libcontainer now integrates CRIU for checkpointing and restoring containers. This lets you save the state of a process running inside a container to disk, and then restore that state into a new process, on the same machine or on another machine.
criu version 1.5.2 or higher is required to use checkpoint and restore.
If you don't already have criu installed, you can build it from source, following the
online instructions. criu is also installed in the docker image
generated when building libcontainer with docker.
Copyright and license
Code and documentation copyright 2014 Docker, inc. The code and documentation are released under the Apache 2.0 license. The documentation is also released under Creative Commons Attribution 4.0 International License. You may obtain a copy of the license, titled CC-BY-4.0, at http://creativecommons.org/licenses/by/4.0/.