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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Message-ID: <84889d57a3943f47b3ee0df6d1ff25c2.squirrel@webmail-b.css.fujitsu.com>
Date:	Wed, 16 Sep 2009 21:06:48 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	Am?rico_Wang <xiyou.wangcong@...il.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"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

Am.$(D+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.

Sorry,
-Kame


> Thanks.
> --
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