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

Link: http://lkml.kernel.org/r/20171122121921.64822-1-kirill.shutemov@linux.intel.com


Fixes: c2febafc ("mm: convert generic code to 5-level paging")
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>	[4.11+]

Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5d38f049

mm/hugetlb.c

+3 −1
Original line number Diff line number Diff line
@@ -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) {