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Subject: Re: [PATCH next] sysctl: add proc_dointvec_jiffies_minmax to limit
 the min/max write value
From:   Zhiqiang Liu <liuzhiqiang26@huawei.com>
To:     Kees Cook <keescook@chromium.org>, <akpm@linux-foundation.org>
CC:     <mcgrof@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>, <ebiederm@xmission.com>,
        <pbonzini@redhat.com>, <viro@zeniv.linux.org.uk>,
        <adobriyan@gmail.com>, <mingfangsen@huawei.com>,
        <wangxiaogang3@huawei.com>, "Zhoukang (A)" <zhoukang7@huawei.com>,
        <netdev@vger.kernel.org>
References: <032e024f-2b1b-a980-1b53-d903bc8db297@huawei.com>
 <3e421384-a9cb-e534-3370-953c56883516@huawei.com>
 <d5138655-41a8-0177-ae0d-c4674112bf56@huawei.com>
 <201905150945.C9D1F811F@keescook>
 <dd40ae3b-8e0a-2d55-d402-6f261a6c0e09@huawei.com>
Message-ID: <20d5857e-de44-4f02-5465-7febc57f0a20@huawei.com>
Date:   Mon, 1 Jul 2019 16:06:13 +0800
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friendly ping ...

On 2019/6/4 23:27, Zhiqiang Liu wrote:
>> On Wed, May 15, 2019 at 10:53:55PM +0800, Zhiqiang Liu wrote:
>>
>> (Please include akpm on CC for next versions of this, as he's likely
>> the person to take this patch.)
> Thanks for your advice. And sorry to reply you so late.
> 
>>>>> In proc_dointvec_jiffies func, the write value is only checked
>>>>> whether it is larger than INT_MAX. If the write value is less
>>>>> than zero, it can also be successfully writen in the data.
>>
>> This appears to be "be design", but I see many "unsigned int" users
>> that might be tricked into giant values... (for example, see
>> net/netfilter/nf_conntrack_standalone.c)
>>
>> Should proc_dointvec_jiffies() just be fixed to disallow negative values
>> entirely? Looking at the implementation, it seems to be very intentional
>> about accepting negative values.
>>
>> However, when I looked through a handful of proc_dointvec_jiffies()
>> users, it looks like they're all expecting a positive value. Many in the
>> networking subsystem are, in fact, writing to unsigned long variables,
>> as I mentioned.
>>
> I totally agree with you. And I also cannot find an scenario that expects
> negative values. Consideing the "negative" scenario may be exist, I add the
> proc_dointvec_jiffies_minmax like proc_dointvec_minmax.
> 
>> Are there real-world cases of wanting to set a negative jiffie value
>> via proc_dointvec_jiffies()?
> Until now, I do not find such cases.
> 
>>>>>
>>>>> Here, we add a new func, proc_dointvec_jiffies_minmax, to limit the
>>>>> min/max write value, which is similar to the proc_dointvec_minmax func.
>>>>>
>>
>> If proc_dointvec_jiffies() can't just be fixed, where will the new
>> function get used? It seems all the "unsigned int" users could benefit.
>>
> I tend to add the proc_dointvec_jiffies_minmax func to provide more choices and
> not change the previous use of proc_dointvec_jiffies func.
> 
> Thanks for your reply again.
> 
> 
> .
>