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SubjectRe: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap
Date
On Tue, Apr 11, 2017 at 03:51:58PM -0700, Mike Kravetz wrote:
...
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 7163fe0..dde8613 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -136,17 +136,26 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
> vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
> vma->vm_ops = &hugetlb_vm_ops;
>
> + /*
> + * Offset passed to mmap (before page shift) could have been
> + * negative when represented as a (l)off_t.
> + */
> + if (((loff_t)vma->vm_pgoff << PAGE_SHIFT) < 0)
> + return -EINVAL;
> +
> if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
> return -EINVAL;
>
> vma_len = (loff_t)(vma->vm_end - vma->vm_start);
> + len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> + /* check for overflow */
> + if (len < vma_len)
> + return -EINVAL;

Andrew sent this patch to Linus today, so I know it's a little too late, but
I think that getting len directly from vma like below might be a simpler fix.

len = (loff_t)(vma->vm_end - vma->vm_start + (vma->vm_pgoff << PAGE_SHIFT));

This shouldn't overflow because vma->vm_{end|start|pgoff} are unsigned long,
but if worried you can add VM_BUG_ON_VMA(len < 0, vma).

Thanks,
Naoya Horiguchi

>
> inode_lock(inode);
> file_accessed(file);
>
> ret = -ENOMEM;
> - len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> -
> if (hugetlb_reserve_pages(inode,
> vma->vm_pgoff >> huge_page_order(h),
> len >> huge_page_shift(h), vma,
> @@ -155,7 +164,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
>
> ret = 0;
> if (vma->vm_flags & VM_WRITE && inode->i_size < len)
> - inode->i_size = len;
> + i_size_write(inode, len);
> out:
> inode_unlock(inode);
>
> --
> 2.7.4
>
>

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