linux-kernel - Re: [RFC][PATCH][bugfix] more checks for negative f_pos handling (Was Re: Question: how to handle too big f

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Date:	Thu, 17 Sep 2009 11:06:18 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>, viro@...iv.linux.org.uk,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	oleg@...hat.com
Subject: Re: [RFC][PATCH][bugfix] more checks for negative f_pos handling (Was 
	Re: Question: how to handle too big f_pos

2009/9/16 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>:
> Am�+1rico_Wang wrote:
>> On Wed, Sep 16, 2009 at 4:44 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@...fujitsu.com> wrote:
>>> Ah, sorry. I should CC: you.
>>
>>
>> No problem. :)
>>
>>>> > --- mmotm-2.6.31-Sep14.orig/fs/proc/base.c
>>>> > +++ mmotm-2.6.31-Sep14/fs/proc/base.c
>>>> > @@ -903,18 +903,30 @@ out_no_task:
>>>> >
>>>> > ?loff_t mem_lseek(struct file *file, loff_t offset, int orig)
>>>> > ?{
>>>> > + ? ? ? struct task_struct *task =
>>>> get_proc_task(file->f_path.dentry->d_inode);
>>>> > + ? ? ? unsigned long long new_offset = -EINVAL;
>>>>
>>>>
>>>> Why not make 'new_offset' as loff_t? This can make your code easier.
>>>>
>>> loff_t is "long long", I wanted "unsigned long long" for showing
>>> f_pos here is treated as "unsigned".
>>>
>>
>>
>> Yeah, the same as for __verify_negative_pos_range(), right...
>>
>>
>> <snip>
>>
>>>> > ? ? ? ?}
>>>> > - ? ? ? force_successful_syscall_return();
>>>> > - ? ? ? return file->f_pos;
>>>> > + ? ? ? if (new_offset < (unsigned long long)TASK_SIZE_OF(task)) {
>>>>
>>>>
>>>> Hmm, why this check?
>>>>
>>> 2 reasons.
>>>
>>> ?1. If this lseek has to check something, this is it.
>>> ?2. On architecture where 32bit program can ran on 64bit,
>>> ? ? moving f_pos above 4G is out-of-range, for example.
>>>
>>> But mem_read() will catch any bad f_pos, anyway. So, just making
>>> allow all f_pos here is maybe a choice. Considering lseek,
>>> providing this range check here is not so bad.
>>
>> Ok, I misunderstood the macro 'TASK_SIZE_OF', then no problem.
>>
>> Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>
>>
> Ah, very sorry. I noticed I didn't handle pread/pwrite, splice, etc...
> I'll do retry.

Yes? Not necessary...

In man page, it said /proc/<pid>/mem can be accessed via open(),
read(), fseek(), no pread(), no splice()...
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