| 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), |
| _ |
