Commit f4f0a3d8 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

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

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.

Fixes: c2febafc ("mm: convert generic code to 5-level paging")
Signed-off-by: default avatarKirill A. Shutemov <>
Acked-by: default avatarVlastimil Babka <>
Acked-by: default avatarMichal Hocko <>
Cc: <>	[4.11+]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 5d38f049
......@@ -4635,7 +4635,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
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) {
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