From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kirill A. Shutemov" Subject: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine Date: Wed, 22 Nov 2017 15:19:21 +0300 Message-ID: <20171122121921.64822-1-kirill.shutemov@linux.intel.com> Return-path: Sender: stable-owner@vger.kernel.org To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Michal Hocko , "Kirill A. Shutemov" , stable@vger.kernel.org List-Id: linux-api@vger.kernel.org I've made 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. Signed-off-by: Kirill A. Shutemov Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") Cc: # v4.11+ --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2d2ff5e8bf2b..94a4c0b63580 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4617,7 +4617,9 @@ 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) { -- 2.15.0