Commit d08af0a5 authored by Joao Martins's avatar Joao Martins Committed by Linus Torvalds

mm/hugetlb: fix refs calculation from unaligned @vaddr

Commit 82e5d378 ("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: 82e5d378 ("mm/hugetlb: refactor subpage recording")
Reported-by: syzbot+a3fcd59df1b372066f5a@syzkaller.appspotmail.com
Signed-off-by: default avatarJoao Martins <joao.m.martins@oracle.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b3b2177a
......@@ -5440,8 +5440,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
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),
......
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