From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxx Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [4.11+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff -puN mm/hugetlb.c~mm-hugetlb-fix-null-pointer-dereference-on-5-level-paging-machine mm/hugetlb.c --- a/mm/hugetlb.c~mm-hugetlb-fix-null-pointer-dereference-on-5-level-paging-machine +++ a/mm/hugetlb.c @@ -4635,7 +4635,9 @@ 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) { _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
