csi-snapshot-controller crashes when processing VolumeSnapshot with non-existing PVC

Report Submission Form ## Summary: csi-snapshot-controller crashes when processing VolumeSnapshot with non-existing PVC ## Kubernetes Version: 1.19 ## Component Version: snapshot-controller from external-snapshotter repo ver 3.0.0 https://github.com/kubernetes-csi/external-snapshotter/releases/tag/v3.0.0 ## Steps To Reproduce: 1. Install Kubernetes 1.19 with snapshot-controller v3.0.0 1. Create VolumeSnapshot object with empty spec.volumeSnapshotClass and spec.source.persistentVolumeClaimName = <non-existing PVC name> ``` apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshot metablocked: name: new-snapshot spec: source: persistentVolumeClaimName: blabla ``` 1. watch snapshot-controller die ## Supporting Material/References: [list any additional material (e.g. screenshots, logs, etc.)] snapshot-controller log: ``` E0929 06:42:38.147021 1 snapshot_controller_base.go:338] checkAndUpdateSnapshotClass failed to setDefaultClass the snapshot source PVC name is not specified E0929 06:42:38.147118 1 runtime.go:78] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference) goroutine 161 [running]: k8s.io/apimachinery/pkg/util/runtime.logPanic(0x1446fc0, 0x201e670) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:74 +0xa6 k8s.io/apimachinery/pkg/util/runtime.HandleCrash(0x0, 0x0, 0x0) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:48 +0x89 panic(0x1446fcit sh0, 0x201e670) /usr/lib/golang/src/runtime/panic.go:969 +0x175 github.com/kubernetes-csi/external-snapshotter/v3/pkg/common-controller.(*csiSnapshotCommonController).syncSnapshotByKey(0xc0001f8e00, 0xc0006a6ae0, 0x19, 0x0, 0xbc) /go/src/github.com/kubernetes-csi/external-snapshotter/pkg/common-controller/snapshot_controller_base.go:215 +0x9d7 github.com/kubernetes-csi/external-snapshotter/v3/pkg/common-controller.(*csiSnapshotCommonController).snapshotWorker(0xc0001f8e00) /go/src/github.com/kubernetes-csi/external-snapshotter/pkg/common-controller/snapshot_controller_base.go:188 +0xed k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0xc0006ba8b0) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:155 +0x5f k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc0006ba8b0, 0x1774260, 0xc0001f0030, 0x1, 0xc00002a1e0) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:156 +0xad k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc0006ba8b0, 0x0, 0x0, 0x1, 0xc00002a1e0) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:133 +0x98 k8s.io/apimachinery/pkg/util/wait.Until(0xc0006ba8b0, 0x0, 0xc00002a1e0) /go/src/github.com/kubernetes-csi/external-snapshotter/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:90 +0x4d created by it shgithub.com/kubernetes-csi/external-snapshotter/v3/pkg/common-controller.(*csiSnapshotCommonController).Run /go/src/github.com/kubernetes-csi/external-snapshotter/pkg/common-controller/snapshot_controller_base.go:139 +0x2ae panic: runtime error: invalid memory address or nil pointer dereference [recovered] panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0xa0 pc=0x12b1d97] ``` Note: * This has been already **publicly reported** by Qin Ping, [email protected] at https://bugzilla.redhat.com/show_bug.cgi?id=1883421. She should get credit for discovering the issue and bounty if possible. China has national holiday until Oct 8th, so I'm filling the report. * I already fixed it upstream ( https://github.com/kubernetes-csi/external-snapshotter/issues/380, https://github.com/kubernetes-csi/external-snapshotter/pull/381) and only later realized its security impacts. * Volume snapshots are Beta feature of Kubernetes 1.19 / external-snapshotter 3.0.0. * external-snapshotter 3.0.0 has been released ~14 days ago and it's probably not widely installed yet. ## Impact DoS of snapshot-controller. It's restarted by Kubernetes, but it dies processing the same VolumeSnapshot again and again. * Users can't create snapshots of their volumes. * Kubernetes (snapshot-controller) does not clean up VolumeSnapshotContent objects when user deletes a VolumeSnapshot and its Retain policy is Delete. All other Kubernetes functionality is not impacted.