| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 20/95] mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine | Date | Mon, 4 Dec 2017 16:59:44 +0100 |
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4.14-stable review patch. If anyone has any objections, please let me know.
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From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
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.
Link: http://lkml.kernel.org/r/20171122121921.64822-1-kirill.shutemov@linux.intel.com Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -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) {
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