linux-kernel - Re: [PATCH next] sysctl: add proc_dointvec_jiffies

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Message-ID: <dd40ae3b-8e0a-2d55-d402-6f261a6c0e09@huawei.com>
Date:   Tue, 4 Jun 2019 23:27:51 +0800
From:   Zhiqiang Liu <liuzhiqiang26@...wei.com>
To:     Kees Cook <keescook@...omium.org>, <akpm@...ux-foundation.org>
CC:     <mcgrof@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <ebiederm@...ssion.com>,
        <pbonzini@...hat.com>, <viro@...iv.linux.org.uk>,
        <adobriyan@...il.com>, <mingfangsen@...wei.com>,
        <wangxiaogang3@...wei.com>, "Zhoukang (A)" <zhoukang7@...wei.com>,
        <netdev@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH next] sysctl: add proc_dointvec_jiffies_minmax to limit
 the min/max write value

> 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.