linux-kernel - Re: [PATCH] proc/sysctl: fix return error for proc_doulongvec

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Message-ID: <20181206085242.GG28501@garbanzo.do-not-panic.com>
Date:   Thu, 6 Dec 2018 00:52:42 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Cheng Lin <cheng.lin130@....com.cn>, akpm@...ux-foundation.org
Cc:     keescook@...omium.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, zhong.weidong@....com.cn,
        wang.yi59@....com.cn, Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: Re: [PATCH] proc/sysctl: fix return error for proc_doulongvec_minmax

On Thu, Dec 06, 2018 at 03:36:15PM +0800, Cheng Lin wrote:
> If the number of input parameters is less than the total
> parameters, an EINVAL error will be returned.
> 
> e.g.
> We use proc_doulongvec_minmax to pass up to two parameters
> with kern_table.
> 
> {
> 	.procname       = "monitor_signals",
> 	.data           = &monitor_sigs,
> 	.maxlen         = 2*sizeof(unsigned long),
> 	.mode           = 0644,
> 	.proc_handler   = proc_doulongvec_minmax,
> },
> 
> Reproduce:
> When passing two parameters, it's work normal. But passing
> only one parameter, an error "Invalid argument"(EINVAL) is
> returned.
> 
> [root@...50 ~]# echo 1 2 > /proc/sys/kernel/monitor_signals
> [root@...50 ~]# cat /proc/sys/kernel/monitor_signals
> 1       2
> [root@...50 ~]# echo 3 > /proc/sys/kernel/monitor_signals
> -bash: echo: write error: Invalid argument
> [root@...50 ~]# echo $?
> 1
> [root@...50 ~]# cat /proc/sys/kernel/monitor_signals
> 3       2
> [root@...50 ~]#
> 
> The following is the result after apply this patch. No error
> is returned when the number of input parameters is less than
> the total parameters.
> 
> [root@...50 ~]# echo 1 2 > /proc/sys/kernel/monitor_signals
> [root@...50 ~]# cat /proc/sys/kernel/monitor_signals
> 1       2
> [root@...50 ~]# echo 3 > /proc/sys/kernel/monitor_signals
> [root@...50 ~]# echo $?
> 0
> [root@...50 ~]# cat /proc/sys/kernel/monitor_signals
> 3       2
> [root@...50 ~]#
> 
> There are three processing functions dealing with digital parameters,
> __do_proc_dointvec/__do_proc_douintvec/__do_proc_doulongvec_minmax.
> 
> This patch deals with __do_proc_doulongvec_minmax, just as
> __do_proc_dointvec does, adding a check for parameters 'left'. In
> __do_proc_douintvec, its code implementation explicitly does not
> support multiple inputs.
> 
> static int __do_proc_douintvec(...){
>          ...
>          /*
>           * Arrays are not supported, keep this simple. *Do not* add
>           * support for them.
>           */
>          if (vleft != 1) {
>                  *lenp = 0;
>                  return -EINVAL;
>          }
>          ...
> }
> 
> So, just __do_proc_doulongvec_minmax has the problem. And most use of
> proc_doulongvec_minmax/proc_doulongvec_ms_jiffies_minmax just have one
> parameter.
> 
> Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>

Thanks for fixing up the commit log.

Acked-by: Luis Chamberlain <mcgrof@...nel.org>

I think we can live with this outside of stable. So stable is not
needed. But I would not be surprised if autosel algorithm will end
up picking it up. And if so.. well, it cannot hurt.

  Luis