Re: CVE-2024-36000: mm/hugetlb: fix missing hugetlb_lock for resv uncharge

[Michal Hocko <mhocko@suse.com>]

Peter,
does b76b46902c2d ("mm/hugetlb: fix missing hugetlb_lock for resv
uncharge") really have any security implications? I fail to see any but
UFFD is not really my area so I might be missing something very easily.

On Mon 20-05-24 11:48:36, Greg KH wrote:
> 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.
> 
> The Linux kernel CVE team has assigned CVE-2024-36000 to this issue.
> 
> 
> Affected and fixed versions
> ===========================
> 
> 	Issue introduced in 5.10 with commit 79aa925bf239 and fixed in 6.1.91 with commit 4c806333efea
> 	Issue introduced in 5.10 with commit 79aa925bf239 and fixed in 6.6.30 with commit f6c5d21db16a
> 	Issue introduced in 5.10 with commit 79aa925bf239 and fixed in 6.8.9 with commit 538faabf31e9
> 	Issue introduced in 5.10 with commit 79aa925bf239 and fixed in 6.9 with commit b76b46902c2d
> 	Issue introduced in 5.9.7 with commit f87004c0b2bd
> 
> Please see https://www.kernel.org for a full list of currently supported
> kernel versions by the kernel community.
> 
> Unaffected versions might change over time as fixes are backported to
> older supported kernel versions.  The official CVE entry at
> 	https://cve.org/CVERecord/?id=CVE-2024-36000
> will be updated if fixes are backported, please check that for the most
> up to date information about this issue.
> 
> 
> Affected files
> ==============
> 
> The file(s) affected by this issue are:
> 	mm/hugetlb.c
> 
> 
> Mitigation
> ==========
> 
> The Linux kernel CVE team recommends that you update to the latest
> stable kernel version for this, and many other bugfixes.  Individual
> changes are never tested alone, but rather are part of a larger kernel
> release.  Cherry-picking individual commits is not recommended or
> supported by the Linux kernel community at all.  If however, updating to
> the latest release is impossible, the individual changes to resolve this
> issue can be found at these commits:
> 	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

-- 
Michal Hocko
SUSE Labs