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:	Wed, 16 Sep 2009 17:13:58 +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

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>

Thanks.
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