CVE-2022-48700

In the Linux kernel, the following vulnerability has been resolved:

vfio/type1: Unpin zero pages

Theres currently a reference count leak on the zero page. We increment the reference via pin_user_pages_remote(), but the page is later handled as an invalid/reserved page, therefore its not accounted against the user and not unpinned by our put_pfn().

Introducing special zero page handling in put_pfn() would resolve the leak, but without accounting of the zero page, a single user could still create enough mappings to generate a reference count overflow.

The zero page is always resident, so for our purposes theres no reason to keep it pinned. Therefore, add a loop to walk pages returned from pin_user_pages_remote() and unpin any zero pages.

Affected Software

References

• https://git.kernel.org/stable/c/5321908ef74fb593e0dbc8737d25038fc86c9986
• https://git.kernel.org/stable/c/578d644edc7d2c1ff53f7e4d0a25da473deb4a03
• https://git.kernel.org/stable/c/5d721bf222936f5cf3ee15ced53cc483ecef7e46
• https://git.kernel.org/stable/c/873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4