Re: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Vegard Nossum <vegard.nossum@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Hillf Danton <hillf.zj@alibaba-inc.com>,
	Michal Hocko <mhocko@suse.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap
Date: Fri, 14 Apr 2017 03:32:15 +0000	[thread overview]
Message-ID: <20170414033210.GA12973@hori1.linux.bs1.fc.nec.co.jp> (raw)
In-Reply-To: <1491951118-30678-1-git-send-email-mike.kravetz@oracle.com>

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
> 
> 