linux-kernel - [PATCH 4.14 20/95] mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine

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Message-Id: <20171204160047.010076427@linuxfoundation.org>
Date:   Mon,  4 Dec 2017 16:59:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 20/95] mm/hugetlb: fix NULL-pointer dereference on 5-level paging machine

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kirill A. Shutemov <kirill.shutemov@...ux.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@...ux.intel.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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) {