From: Joao Martins joao.m.martins@oracle.com Subject: mm/hugetlb: fix refs calculation from unaligned @vaddr
commit 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording") refactored the count of subpages but missed an edge case when @vaddr is not aligned to PAGE_SIZE e.g. when close to vma->vm_end. It would then errousnly set @refs to 0 and record_subpages_vmas() wouldn't set the @pages array element to its value, consequently causing the reported null-deref by syzbot.
Fix it by aligning down @vaddr by PAGE_SIZE in @refs calculation.
Link: https://lkml.kernel.org/r/20210713152440.28650-1-joao.m.martins@oracle.com Fixes: 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording") Reported-by: syzbot+a3fcd59df1b372066f5a@syzkaller.appspotmail.com Signed-off-by: Joao Martins joao.m.martins@oracle.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/hugetlb.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-fix-refs-calculation-from-unaligned-vaddr +++ a/mm/hugetlb.c @@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struc continue; }
- refs = min3(pages_per_huge_page(h) - pfn_offset, - (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder); + /* vaddr may not be aligned to PAGE_SIZE */ + refs = min3(pages_per_huge_page(h) - pfn_offset, remainder, + (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
if (pages || vmas) record_subpages_vmas(mem_map_offset(page, pfn_offset), _