linux-kernel - Re: [f2fs-dev][PATCH 1/2] f2fs: check name_len of dir entry to prevent from deadloop

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Date:	Fri, 4 Jul 2014 23:43:13 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	Changman Lee <cm224.lee@...sung.com>,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [f2fs-dev][PATCH 1/2] f2fs: check name_len of dir entry to
 prevent from deadloop

Hi Chao,

On Wed, Jul 02, 2014 at 01:23:47PM +0800, Chao Yu wrote:
> We assume that modification of some special application could result in zeroed
> name_len, or it is consciously made by somebody. We will deadloop in
> find_in_block when name_len of dir entry is zero.

Could you explain this a little bit more?
I'm not sure how it can happen.
I think the zeroed name_len would cause some problems in f2fs_add_link.

Thanks,

> 
> This patch is added for preventing deadloop in above scenario.
> 
> Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> ---
>  fs/f2fs/dir.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index be8c7af..4316ec5 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -121,6 +121,16 @@ static struct f2fs_dir_entry *find_in_block(struct page *dentry_page,
>  			}
>  		}
>  
> +		/* check name_len to prevent from deadloop here */
> +		if (unlikely(de->name_len == 0)) {
> +			struct inode *inode = dentry_page->mapping->host;
> +
> +			f2fs_msg(inode->i_sb, KERN_ERR,
> +				"zero-length dir entry, ino = %lu, name = %s",
> +				(unsigned long)inode->i_ino, name->name);
> +			break;
> +		}
> +
>  		bit_start = bit_pos
>  				+ GET_DENTRY_SLOTS(le16_to_cpu(de->name_len));
>  	}
> -- 
> 1.7.9.5

-- 
Jaegeuk Kim
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