CVE-2022-48700 Information

Description

In the Linux kernel the following vulnerability has been resolved:

vfio/type1: Unpin zero pages

There’s 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 it’s 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 there’s no reason to keep it pinned. Therefore add a loop to walk pages returned from pin_user_pages_remote() and unpin any zero pages.

Reference

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