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Date:   Mon, 24 Jul 2023 04:47:33 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Linke Li <lilinke99@foxmail.com>
Cc:     linux-mm@kvack.org, mike.kravetz@oracle.com, muchun.song@linux.dev,
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        dan.carpenter@linaro.org, Linke Li <lilinke99@gmail.com>
Subject: Re: [PATCH v3] hugetlbfs: Fix integer overflow check in
 hugetlbfs_file_mmap()
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On Thu, Jul 20, 2023 at 10:49:52PM +0800, Linke Li wrote:
> +++ b/fs/hugetlbfs/inode.c
> @@ -154,10 +154,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
>  	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)
> +	if (check_add_overflow(vma_len, (loff_t)vma->vm_pgoff << PAGE_SHIFT, &len))
>  		return -EINVAL;

Doesn't this check duplicate that performed by file_mmap_ok()?  Can't we
just delete the check, or is there a code path that leads here while
avoiding file_mmap_ok()?