Re: [PATCH v3] hugetlbfs: Fix integer overflow check in hugetlbfs_file_mmap()

[Mike Kravetz <mike.kravetz@oracle.com>]

On 07/20/23 22:49, Linke Li wrote:
> From: Linke Li <lilinke99@gmail.com>
> 
> ```
> 	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;
> ```
> 
> There is a signed integer overflow in the code, which is undefined
> behavior according to the C stacnard. Although this works, it's
> still a bit ugly and static checkers will complain.
> 
> Using macro "check_add_overflow" to do the overflow check can
> effectively detect integer overflow and avoid any undefined behavior.
> 
> Signed-off-by: Linke Li <lilinke99@gmail.com>
> ---
> v3: fix checkpatch warning and better description.
>  fs/hugetlbfs/inode.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 7b17ccfa039d..326a8c0af5f6 100644
> --- a/fs/hugetlbfs/inode.c
> +++ 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);

I don't think you wanted to delete the above line as ...

> -	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))

.. vma_len is uninitialized here.

>  		return -EINVAL;
>  
>  	inode_lock(inode);
> -- 
> 2.25.1
> 

-- 
Mike Kravetz