New() can panic on OCI specs with a missing root section

[Utkarsh-sharma47]

Description

New() currently validates that the parsed OCI spec contains a linux section, but does not validate that spec.Root is present.

A syntactically valid but structurally incomplete config.json, such as:

{
  "linux": {}
}

can therefore reach code paths that dereference spec.Root.Path, resulting in a nil pointer panic instead of returning a validation error.

I also found that when valid unikernel annotations are present, New() can return successfully while u.Spec.Root == nil, leaving an invalid Unikontainer that may panic later.

Relevant code

New() currently checks:

if spec == nil || spec.Linux == nil {
    return nil, fmt.Errorf("invalid OCI spec: linux section is required")
}

but GetUnikernelConfig() later uses:

rootFSDir := spec.Root.Path

and other paths such as InitialSetup() and Exec() also access u.Spec.Root.Path.

Minimal reproducer

Create a bundle containing:

{
  "linux": {}
}

as config.json and call New() with that bundle.

Actual behavior

urunc can panic with a nil pointer dereference when the configuration fallback path accesses spec.Root.Path.

A spec containing valid unikernel annotations but no root section can also be accepted by New(), leaving Spec.Root == nil.

Expected behavior

Structurally incomplete OCI specs should be be rejected with a validation error, for example:

invalid OCI spec: root section is required

Possible direction

Validate that spec.Root is present before returning from New() / Get(), alongside the existing validation of spec.Linux.

A regression test using a minimal spec with linux present and root missing could cover this case.

[cmainas]

Hello @Utkarsh-sharma47 ,

can you please format the description of the issue correctly, you can use code blocks.

[Utkarsh-sharma47]

Hi @cmainas, thanks again for the formatting suggestion—I’ve updated the issue accordingly.

I also opened PR #903 with a proposed fix and regression tests for this issue. Whenever you have time, I’d appreciate any feedback or review. Thanks!