linux-kernel - Re: [RFC][PATCH] vfs: always protect diretory file->fpos with inode mutex

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Date:	Tue, 19 Feb 2013 20:43:14 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	<gnehzuil.liu@...il.com>
CC:	<linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>, "Theodore Ts'o" <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<andi@...stfloor.org>, Wuqixuan <wuqixuan@...wei.com>,
	Al Viro <viro@...IV.linux.org.uk>, <gregkh@...uxfoundation.org>
Subject: Re: [RFC][PATCH] vfs: always protect diretory file->fpos with inode
 mutex

On 2013/2/19 20:33, Zheng Liu wrote:
> On Tue, Feb 19, 2013 at 09:22:40AM +0800, Li Zefan wrote:
>> There's a long long-standing bug...As long as I don't know when it dates
>> from.
>>
>> I've written and attached a simple program to reproduce this bug, and it can
>> immediately trigger the bug in my box. It uses two threads, one keeps calling
>> read(), and the other calling readdir(), both on the same directory fd.
> 
> Hi Zefan,
> 
> Out of curiosity, why do you call read(2) on a directory fd?  I only
> open(2) a directory in order to execute a flush operation to make sure
> that a file is really created.
> 

Because something wrong happened in userspace programs.

After a thread closed a socket, another thread is still reading data from
this socket, but the socket fd has been re-used for opening directory for
readdir()!

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