From: Joao Martins <joao.m.martins@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 82e5d378b0e47 ("mm/hugetlb: refactor subpage recording")
Reported-by: syzbot+a3fcd59df1b372066f5a@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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),
_
