CVE-2021-47214 Information

Description

In the Linux kernel the following vulnerability has been resolved:

hugetlb userfaultfd: fix reservation restore on userfaultfd error

Currently in the is_continue case in hugetlb_mcopy_atomic_pte() if we bail out using \goto out_release_unlock;\ in the cases where idx >= size or !huge_pte_none() the code will detect that new_pagecache_page == false and so call restore_reserve_on_error(). In this case I see restore_reserve_on_error() delete the reservation and the following call to remove_inode_hugepages() will increment h->resv_hugepages causing a 100% reproducible leak.

We should treat the is_continue case similar to adding a page into the pagecache and set new_pagecache_page to true to indicate that there is no reservation to restore on the error path and we need not call restore_reserve_on_error(). Rename new_pagecache_page to page_in_pagecache to make that clear.

Reference

https://git.kernel.org/stable/c/b5069d44e2fbc4a9093d005b3ef0949add3dd27e https://git.kernel.org/stable/c/cc30042df6fcc82ea18acf0dace831503e60a0b7