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containers/image: remove signatures when copying in to OCI layout #1664

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May 5, 2025
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containers/image: remove signatures when copying in to OCI layout #1664

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7 changes: 7 additions & 0 deletions pkg/image/containersimageregistry/registry.go
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,13 @@ func (r *Registry) Pull(ctx context.Context, ref orimage.Reference) error {
SourceCtx: sourceCtx,
DestinationCtx: r.cache.getSystemContext(),
OptimizeDestinationImageAlreadyExists: true,

// We use the OCI layout as a temporary storage and
// pushing signatures for OCI images is not supported
// so we remove the source signatures when copying.
// Signature validation will still be performed
// accordingly to a provided policy context.
RemoveSignatures: true,
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Maybe we also want

PreserveDigests: true,

It doesn't impact this particular operation, but it also seems a good option which doesn't default on.
I verified that this works with upstream (unsigned) and downstream (signed) example catalogs.

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GoDoc for that field is:

// Preserve digests, and fail if we cannot.

I'm hesitant about the "fail if we cannot" part. We have similar code in operator-controller that does not set this value, so I don't think it is necessary, and likely not for this bug fix specifically.

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I agree that it's not necessary for resolving this bug. But the bug arose because we didn't consider other fields that might've been pertinent when we introduced the new containers/image registry support, so it felt like we should at least discuss any other possible missed configuration.

I think we can agree that mutating digests across our local copy would be an undesirable side effect.

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On second thought, even skopeo has this option as a non-main-path flag, which suggests that there are conditions under which this is desirable, but not in general.
If we wanted this, we should plumb through a controlling flag. Which I don't think we need to do, at this time.

}); err != nil {
return err
}
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