The Linux Foundation maintains a comprehensive umbrella of insurance policies to protect its communities' interests. This insurance covers the projects themselves, any employees of the organization and extends to volunteers who are working with LF projects. For those contributors who work on LF projects on behalf of member companies, those companies' own insurance policies also provide coverage and would most likely be the primary source of protection for those contributors.
More importantly than insurance coverage levels, the Linux Foundation works every day to reduce risks that would ever lead to needing insurance at all. LF's in-house legal team works with some of the foremost intellectual property / trademark / export control lawyers in the world to ensure that LF projects and communities are established and organized with specific frameworks and are operated in specific manners that protect the communities from legal exposure. In addition to regularly updated guidelines regarding best practices that projects should abide by (https://www.linuxfoundation.org/resources/publications/ and https://www.linuxfoundation.org/resources/open-source-guides/), the LF legal team is available to support its projects if more specific guidance if needed.