Patch "mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-hugetlb-fix-null-pointer-dereference-on-5-level-paging-machine.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Wed, 29 Nov 2017 16:11:30 -0800
Subject: mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine

From: Kirill A. Shutemov <[email protected]>

commit f4f0a3d85b50a65a348e2b8635041d6b30f01deb upstream.

I made a mistake during converting hugetlb code to 5-level paging: in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset().

Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc() if p4d table is not yet allocated.

It only can happen in 5-level paging mode. In 4-level paging mode p4d_offset() always returns pgd, so we are fine.

---
 mm/hugetlb.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -4625,7 +4625,9 @@ pte_t *huge_pte_alloc(struct mm_struct *
 	pte_t *pte = NULL;
 
 	pgd = pgd_offset(mm, addr);
-	p4d = p4d_offset(pgd, addr);
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return NULL;
 	pud = pud_alloc(mm, p4d, addr);
 	if (pud) {
 		if (sz == PUD_SIZE) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/mm-fix-device-dax-pud-write-faults-triggered-by-get_user_pages.patch queue-4.14/mm-hugetlb-fix-null-pointer-dereference-on-5-level-paging-machine.patch queue-4.14/mm-thp-do-not-make-page-table-dirty-unconditionally-in-touch_pd.patch queue-4.14/mm-madvise.c-fix-madvise-infinite-loop-under-special-circumstances.patch