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Samuel Karp
7f5d3c5f4d
A nil CRIImplementation field can cause a nil pointer dereference and
panic during startup recovery.
Prior to this change, the nri.API struct would have a nil cri
(CRIImplementation) field after nri.NewAPI until nri.Register was
called. Register is called mid-way through initialization of the CRI
plugin, but recovery for containers occurs prior to that. Container
recovery includes establishing new exit monitors for existing containers
that were discovered. When a container exits, NRI plugins are given the
opportunity to be notified about the lifecycle event, and this is done
by accessing that CRIImplementation field inside the nri.API. If a
container exits prior to nri.Register being called, access to the
CRIImplementation field can cause a panic.
Here's the call-path:
* The CRI plugin starts running
[here](https://github.com/containerd/containerd/blob/ae71819c4f5e67bb4d5ae76a6b735f29cc25774e/pkg/cri/server/service.go#L222)
* It then [calls into](https://github.com/containerd/containerd/blob/ae71819c4f5e67bb4d5ae76a6b735f29cc25774e/pkg/cri/server/service.go#L227)
`recover()` to recover state from previous runs of containerd
* `recover()` then attempts to recover all containers through
[`loadContainer()`](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/server/restart.go#L175)
* When `loadContainer()` finds a container that is still running, it waits
for the task (internal containerd object) to exit and sets up
[exit monitoring](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/server/restart.go#L391)
* Any exit that then happens must be
[handled](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/server/events.go#L145)
* Handling an exit includes
[deleting the Task](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/server/events.go#L188)
and specifying [`nri.WithContainerExit`](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/nri/nri_api_linux.go#L348)
to [notify](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/nri/nri_api_linux.go#L356)
any subscribed NRI plugins
* NRI plugins need to know information about the pod (not just the sandbox),
so before a plugin is notified the NRI API package
[queries the Sandbox Store](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/nri/nri_api_linux.go#L232)
through the CRI implementation
* The `cri` implementation member field in the `nri.API` struct is set as part of the
[`Register()`](https://github.com/containerd/containerd/blob/ae7d74b9e21bd08260586db104a1fe04af754545/internal/cri/nri/nri_api_linux.go#L66) method
* The `nri.Register()` method is only called
[much further down in the CRI `Run()` method](https://github.com/containerd/containerd/blob/ae71819c4f5e67bb4d5ae76a6b735f29cc25774e/pkg/cri/server/service.go#L279)
(manually backported from commit 10aec359a0)
Signed-off-by: Samuel Karp <samuelkarp@google.com>