ig panics when it fails to create container-collection

[alban]

Description

ig panics when it fails to create container-collection

Impact

time="2024-05-07T10:43:32Z" level=info msg="Experimental features enabled"
time="2024-05-07T10:43:36Z" level=warning msg="Failed to create container-collection"
time="2024-05-07T10:43:37Z" level=warning msg="Failed to create container-collection"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1fd12bd]

goroutine 1 [running]:
github.com/inspektor-gadget/inspektor-gadget/pkg/operators/localmanager.(*localManagerTraceWrapper).PreStart(0xc003914180, {0x2f5d840, 0xc0036de000})
        /go/src/github.com/inspektor-gadget/inspektor-gadget/pkg/operators/localmanager/localmanager.go:532 +0xbd
github.com/inspektor-gadget/inspektor-gadget/pkg/gadget-context.(*GadgetContext).run(0xc0036de000, {0xc0036dc0f0, 0x4, 0xc0015c7a00?})
        /go/src/github.com/inspektor-gadget/inspektor-gadget/pkg/gadget-context/run.go:101 +0x1a7
github.com/inspektor-gadget/inspektor-gadget/pkg/gadget-context.(*GadgetContext).Run(0xc0036de000, 0xc0036d20f0?)
        /go/src/github.com/inspektor-gadget/inspektor-gadget/pkg/gadget-context/run.go:158 +0x9e
github.com/inspektor-gadget/inspektor-gadget/pkg/runtime/local.(*Runtime).RunOCIGadget(0x22257e0?, {0x2f868a0?, 0xc0036de000?}, 0xd?, 0xc0015c7b18?)
        /go/src/github.com/inspektor-gadget/inspektor-gadget/pkg/runtime/local/oci.go:35 +0x27
github.com/inspektor-gadget/inspektor-gadget/cmd/common.NewRunCommand.func2(0xc00067c000, {0xc00061b8c0?, 0x3?, 0x3?})
        /go/src/github.com/inspektor-gadget/inspektor-gadget/cmd/common/oci.go:174 +0x697
github.com/spf13/cobra.(*Command).execute(0xc00067c000, {0xc00061b8c0, 0x3, 0x3})
        /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:983 +0xabc
github.com/spf13/cobra.(*Command).ExecuteC(0xc000005b00)
        /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1115 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
        /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1039
main.main()
        /go/src/github.com/inspektor-gadget/inspektor-gadget/cmd/ig/main.go:89 +0x374

Environment and steps to reproduce

I don't have the steps or the environment, I'll try to find more details.

Start ig in a Kubernetes pod:

ig run albantest.azurecr.io/trace_udns:t1 -o json

Expected behavior

ig should not panic.

Additional information

https://github.com/inspektor-gadget/inspektor-gadget/blob/v0.27.0/pkg/operators/localmanager/localmanager.go#L532

func (l *localManagerTraceWrapper) PreStart(gadgetCtx operators.GadgetContext) error {
	// hack - this makes it possible to use the Attacher interface
	var ok bool
	l.gadgetInstance, ok = gadgetCtx.GetVar("ebpfInstance")
	if !ok {
		return fmt.Errorf("getting ebpfInstance")
	}

	compat.Subscribe(
		l.eventWrappers,
		l.manager.igManager.ContainerCollection.EnrichEventByMntNs,
		l.manager.igManager.ContainerCollection.EnrichEventByNetNs,
		0,
	)

Presumably, l.manager.igManager.ContainerCollection is nil. The function PreStart should check this.

cc @flyth

[alban]

I tried to synthetise the error with:

--- a/pkg/container-collection/options.go
+++ b/pkg/container-collection/options.go
@@ -672,7 +672,7 @@ func WithContainerFanotifyEbpf() ContainerCollectionOption {
                        }
                        return true
                })
-               return nil
+               return fmt.Errorf("lets fail on WithContainerFanotifyEbpf")
        }
 }
 

And then run:

go run -exec 'sudo -E' ./cmd/ig/... trace exec --host -c mycontainer

So I get the warnings:

WARN[0000] Failed to create container-collection        
WARN[0000] container-collection isn't available: container enrichment and filtering won't work 

But localManagerTraceWrapper.PreStart is not called in my tests. PreStart has the same interface as other PreStart functions. In fact, when I add a panic() in GadgetContext.run, it is not called.

I am not sure of the differences between LocalManager, localManagerTrace and localManagerTraceWrapper.