CVE-2022-23495: go-merkledag's ProtoNode may be modified such that common method calls may panic

Impact

A ProtoNode may be modified in such a way as to cause various encode errors which will trigger a panic on common method calls that don't allow for error returns.

A ProtoNode should only be able to encode to valid DAG-PB, attempting to encode invalid DAG-PB forms will result in an error from the codec. Manipulation of an existing (newly created or decoded) ProtoNode using the modifier methods did not account for certain states that would place the ProtoNode into an unencodeable form.

Due to conformance with the github.com/ipfs/go-block-format#Block and github.com/ipfs/go-ipld-format#Node interfaces, certain methods, which internally require a re-encode if state has changed, will panic due to the inability to return an error.

Additionally, use of the ProtoNode#SetCidBuilder() method to set a non-functioning CidBuilder (such as one that refers to a multihash where an implementation of that hash function is not available) may cause the same methods to panic as a new CID is required but cannot be created.

Patches

Releases involving fixes for this issue are v0.8.0 and v0.8.1. The recommended minimum version is v0.8.1.

• Additional checks are performed on ProtoNode state changes to avoid the possibility of creating unencodeable forms, errors are returned where this is the case.
• The builder passed in to SetCidBuilder() is inspected to attempt to determine if it is usable to generate CIDs, otherwise an error is returned.
• The panics have been removed and replaced with default values (empty byte slice for RawData() and a default zero-bytes DAG-PB CID for methods involving CIDs).

Workarounds

These workarounds are available when using impacted versions to avoid panic conditions, and may be generally appropriate in order to provide meaningful feedback to users and avoid generating bad, or unexpected encoded data:

• Sanitise inputs when allowing user-input to set a new CidBuilder on a ProtoNode.
• Sanitise Tsize (Link#Size) values such that they are a reasonable byte-size for sub-DAGs where derived from user-input.

References

• https://github.com/ipfs/kubo/issues/9297
• https://github.com/ipfs/go-merkledag/issues/90
• https://github.com/ipfs/go-merkledag/releases/tag/v0.8.0
• https://github.com/ipfs/go-merkledag/pull/91
• https://github.com/ipfs/go-merkledag/pull/92
• https://github.com/ipfs/go-merkledag/pull/93
• https://github.com/ipfs/go-merkledag/releases/tag/v0.8.1

Credit

Thanks to @mrd0ll4r for reporting the original error to Kubo!