Fix kubelet cadvisor stats runtime panic

Fixing a kubelet runtime panic when the runtime returns incomplete data:

```
E0729 08:17:47.260393    5218 panic.go:115] "Observed a panic" panic="runtime error: index out of range [0] with length 0" panicGoValue="runtime.boundsError{x:0, y:0, signed:true, code:0x0}" stacktrace=<
        goroutine 174 [running]:
        k8s.io/apimachinery/pkg/util/runtime.logPanic({0x33631e8, 0x4ddf5c0}, {0x2c9bfe0, 0xc000a563f0})
                k8s.io/apimachinery/pkg/util/runtime/runtime.go:107 +0xbc
        k8s.io/apimachinery/pkg/util/runtime.handleCrash({0x33631e8, 0x4ddf5c0}, {0x2c9bfe0, 0xc000a563f0}, {0x4ddf5c0, 0x0, 0x10000000043c9e5?})
                k8s.io/apimachinery/pkg/util/runtime/runtime.go:82 +0x5e
        k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0xc000ae08c0?})
                k8s.io/apimachinery/pkg/util/runtime/runtime.go:59 +0x108
        panic({0x2c9bfe0?, 0xc000a563f0?})
                runtime/panic.go:785 +0x132
        k8s.io/kubernetes/pkg/kubelet/stats.(*cadvisorStatsProvider).ImageFsStats(0xc000535d10, {0x3363348, 0xc000afa330})
                k8s.io/kubernetes/pkg/kubelet/stats/cadvisor_stats_provider.go:277 +0xaba
        k8s.io/kubernetes/pkg/kubelet/images.(*realImageGCManager).GarbageCollect(0xc000a3c820, {0x33631e8?, 0x4ddf5c0?}, {0x0?, 0x0?, 0x4dbca20?})
                k8s.io/kubernetes/pkg/kubelet/images/image_gc_manager.go:354 +0x1d3
        k8s.io/kubernetes/pkg/kubelet.(*Kubelet).StartGarbageCollection.func2()
                k8s.io/kubernetes/pkg/kubelet/kubelet.go:1472 +0x58
        k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0x30?)
                k8s.io/apimachinery/pkg/util/wait/backoff.go:226 +0x33
        k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc000add110, {0x3330380, 0xc000afa300}, 0x1, 0xc0000ac150)
                k8s.io/apimachinery/pkg/util/wait/backoff.go:227 +0xaf
        k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc000add110, 0x45d964b800, 0x0, 0x1, 0xc0000ac150)
                k8s.io/apimachinery/pkg/util/wait/backoff.go:204 +0x7f
        k8s.io/apimachinery/pkg/util/wait.Until(...)
                k8s.io/apimachinery/pkg/util/wait/backoff.go:161
        created by k8s.io/kubernetes/pkg/kubelet.(*Kubelet).StartGarbageCollection in goroutine 1
                k8s.io/kubernetes/pkg/kubelet/kubelet.go:1470 +0x247
```

This commit fixes panics if:

- `len(imageStats.ImageFilesystems) == 0`
- `len(imageStats.ContainerFilesystems) == 0`
- `imageStats.ImageFilesystems[0].FsId == nil`
- `imageStats.ContainerFilesystems[0].FsId == nil`
- `imageStats.ImageFilesystems[0].UsedBytes == nil`
- `imageStats.ContainerFilesystems[0].UsedBytes == nil`

It also fixes the wrapped `nil` error for the check: `err != nil ||
imageStats == nil` in case that `imageStats == nil`.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

pkg/kubelet/stats/cadvisor_stats_provider.go

@@ -270,26 +270,34 @@ func (p *cadvisorStatsProvider) ImageFsStats(ctx context.Context) (imageFsRet *s
 		return imageFs, imageFs, nil
 	}
 	imageStats, err := p.imageService.ImageFsInfo(ctx)
-	if err != nil || imageStats == nil {
+	if err != nil {
-		return nil, nil, fmt.Errorf("failed to get image stats: %v", err)
+		return nil, nil, fmt.Errorf("failed to get image stats: %w", err)
+	}
+	if imageStats == nil || len(imageStats.ImageFilesystems) == 0 || len(imageStats.ContainerFilesystems) == 0 {
+		return nil, nil, fmt.Errorf("missing image stats: %+v", imageStats)
 	}
 	splitFileSystem := false
-	if imageStats.ImageFilesystems[0].FsId.Mountpoint != imageStats.ContainerFilesystems[0].FsId.Mountpoint {
+	imageFs := imageStats.ImageFilesystems[0]
-		klog.InfoS("Detect Split Filesystem", "ImageFilesystems", imageStats.ImageFilesystems[0], "ContainerFilesystems", imageStats.ContainerFilesystems[0])
+	containerFs := imageStats.ContainerFilesystems[0]
+	if imageFs.FsId != nil && containerFs.FsId != nil && imageFs.FsId.Mountpoint != containerFs.FsId.Mountpoint {
+		klog.InfoS("Detect Split Filesystem", "ImageFilesystems", imageFs, "ContainerFilesystems", containerFs)
 		splitFileSystem = true
 	}
-	imageFs := imageStats.ImageFilesystems[0]
 	var imageFsInodesUsed *uint64
 	if imageFsInfo.Inodes != nil && imageFsInfo.InodesFree != nil {
 		imageFsIU := *imageFsInfo.Inodes - *imageFsInfo.InodesFree
 		imageFsInodesUsed = &imageFsIU
 	}
+	var usedBytes uint64
+	if imageFs.GetUsedBytes() != nil {
+		usedBytes = imageFs.GetUsedBytes().GetValue()
+	}
 
 	fsStats := &statsapi.FsStats{
 		Time:           metav1.NewTime(imageFsInfo.Timestamp),
 		AvailableBytes: &imageFsInfo.Available,
 		CapacityBytes:  &imageFsInfo.Capacity,
-		UsedBytes:      &imageFs.UsedBytes.Value,
+		UsedBytes:      &usedBytes,
 		InodesFree:     imageFsInfo.InodesFree,
 		Inodes:         imageFsInfo.Inodes,
 		InodesUsed:     imageFsInodesUsed,
@@ -305,18 +313,21 @@ func (p *cadvisorStatsProvider) ImageFsStats(ctx context.Context) (imageFsRet *s
 		return nil, nil, fmt.Errorf("failed to get container fs info: %w", err)
 	}
 
-	containerFs := imageStats.ContainerFilesystems[0]
 	var containerFsInodesUsed *uint64
 	if containerFsInfo.Inodes != nil && containerFsInfo.InodesFree != nil {
 		containerFsIU := *containerFsInfo.Inodes - *containerFsInfo.InodesFree
 		containerFsInodesUsed = &containerFsIU
 	}
+	var usedContainerBytes uint64
+	if containerFs.GetUsedBytes() != nil {
+		usedContainerBytes = containerFs.GetUsedBytes().GetValue()
+	}
 
 	fsContainerStats := &statsapi.FsStats{
 		Time:           metav1.NewTime(containerFsInfo.Timestamp),
 		AvailableBytes: &containerFsInfo.Available,
 		CapacityBytes:  &containerFsInfo.Capacity,
-		UsedBytes:      &containerFs.UsedBytes.Value,
+		UsedBytes:      &usedContainerBytes,
 		InodesFree:     containerFsInfo.InodesFree,
 		Inodes:         containerFsInfo.Inodes,
 		InodesUsed:     containerFsInodesUsed,

pkg/kubelet/stats/cadvisor_stats_provider_test.go

@@ -23,6 +23,7 @@ import (
 
 	cadvisorapiv2 "github.com/google/cadvisor/info/v2"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -546,6 +547,86 @@ func TestCadvisorImagesFsStatsKubeletSeparateDiskOff(t *testing.T) {
 	assert.Equal(*imageFsInfo.Inodes-*imageFsInfo.InodesFree, *stats.InodesUsed)
 }
 
+func TestImageFsStatsCustomResponse(t *testing.T) {
+	featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.KubeletSeparateDiskGC, true)
+	for desc, tc := range map[string]struct {
+		response                       *runtimeapi.ImageFsInfoResponse
+		callContainerFsInfo, shouldErr bool
+	}{
+		"image stats are nil": {
+			shouldErr: true,
+		},
+		"no image filesystems in image stats": {
+			response: &runtimeapi.ImageFsInfoResponse{
+				ImageFilesystems:     []*runtimeapi.FilesystemUsage{},
+				ContainerFilesystems: []*runtimeapi.FilesystemUsage{{}},
+			},
+			shouldErr: true,
+		},
+		"no container filesystems in image stats": {
+			response: &runtimeapi.ImageFsInfoResponse{
+				ImageFilesystems:     []*runtimeapi.FilesystemUsage{{}},
+				ContainerFilesystems: []*runtimeapi.FilesystemUsage{},
+			},
+			shouldErr: true,
+		},
+		"image and container filesystem identifiers are nil": {
+			response: &runtimeapi.ImageFsInfoResponse{
+				ImageFilesystems:     []*runtimeapi.FilesystemUsage{{}},
+				ContainerFilesystems: []*runtimeapi.FilesystemUsage{{}},
+			},
+			shouldErr: false,
+		},
+		"using different mountpoints but no used bytes set": {
+			response: &runtimeapi.ImageFsInfoResponse{
+				ImageFilesystems: []*runtimeapi.FilesystemUsage{{
+					FsId: &runtimeapi.FilesystemIdentifier{Mountpoint: "mnt-1"},
+				}},
+				ContainerFilesystems: []*runtimeapi.FilesystemUsage{{
+					FsId: &runtimeapi.FilesystemIdentifier{Mountpoint: "mnt-2"},
+				}},
+			},
+			callContainerFsInfo: true,
+			shouldErr:           false,
+		},
+		"using different mountpoints and set used bytes": {
+			response: &runtimeapi.ImageFsInfoResponse{
+				ImageFilesystems: []*runtimeapi.FilesystemUsage{{
+					FsId:      &runtimeapi.FilesystemIdentifier{Mountpoint: "mnt-1"},
+					UsedBytes: &runtimeapi.UInt64Value{Value: 10},
+				}},
+				ContainerFilesystems: []*runtimeapi.FilesystemUsage{{
+					FsId:      &runtimeapi.FilesystemIdentifier{Mountpoint: "mnt-2"},
+					UsedBytes: &runtimeapi.UInt64Value{Value: 20},
+				}},
+			},
+			callContainerFsInfo: true,
+			shouldErr:           false,
+		},
+	} {
+		ctx := context.Background()
+		mockCadvisor := cadvisortest.NewMockInterface(t)
+		mockRuntime := containertest.NewMockRuntime(t)
+
+		res := getTestFsInfo(1000)
+		mockCadvisor.EXPECT().ImagesFsInfo().Return(res, nil)
+		mockRuntime.EXPECT().ImageFsInfo(ctx).Return(tc.response, nil)
+		if tc.callContainerFsInfo {
+			mockCadvisor.EXPECT().ContainerFsInfo().Return(res, nil)
+		}
+
+		provider := newCadvisorStatsProvider(mockCadvisor, &fakeResourceAnalyzer{}, mockRuntime, nil, NewFakeHostStatsProvider())
+		stats, containerfs, err := provider.ImageFsStats(ctx)
+		if tc.shouldErr {
+			require.Error(t, err, desc)
+			assert.Nil(t, stats)
+			assert.Nil(t, containerfs)
+		} else {
+			assert.NoError(t, err, desc)
+		}
+	}
+}
+
 func TestCadvisorImagesFsStats(t *testing.T) {
 	ctx := context.Background()
 	var (