mm/hugetlb: fix missing hugetlb_lock for resv uncharge

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix missing hugetlb_lock for resv uncharge There is a recent report on UFFDIO_COPY over hugetlb: https://lore.kernel.org/all/000000000000ee06de0616177560@google.com/ 350: lockdep_assert_held(&hugetlb_lock); Should be an issue in hugetlb but triggered in an userfault context, where it goes into the unlikely path where two threads modifying the resv map together. Mike has a fix in that path for resv uncharge but it looks like the locking criteria was overlooked: hugetlb_cgroup_uncharge_folio_rsvd() will update the cgroup pointer, so it requires to be called with the lock held.

References

• https://git.kernel.org/stable/c/4c806333efea1000a2a9620926f560ad2e1ca7cc
• https://git.kernel.org/stable/c/f6c5d21db16a0910152ec8aa9d5a7aed72694505
• https://git.kernel.org/stable/c/538faabf31e9c53d8c870d114846fda958a0de10
• https://git.kernel.org/stable/c/b76b46902c2d0395488c8412e1116c2486cdfcb2