From: Kirill A. Shutemov Date: Thu, 30 Nov 2017 00:11:30 +0000 (-0800) Subject: mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine X-Git-Tag: v4.14.4~76 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=be75ad849b9f3b0512e976a81e31a0beea1419ab;p=platform%2Fkernel%2Flinux-exynos.git mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine 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 Acked-by: Vlastimil Babka Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/hugetlb.c b/mm/hugetlb.c index a2233d7..c539941 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4625,7 +4625,9 @@ 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) {