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

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Date:   Mon, 3 Dec 2018 12:14:36 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     cheng.lin130@....com.cn, keescook@...omium.org,
        akpm@...ux-foundation.org, ebiederm@...ssion.com
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        zhong.weidong@....com.cn, wang.yi59@....com.cn
Subject: Re: Re: [PATCH] proc/sysctl: fix return error for
 proc_doulongvec_minmax

On Mon, Dec 03, 2018 at 01:12:39PM +0800, cheng.lin130@....com.cn wrote:
> >Cheng, thanks for the patch!
> >
> >On Fri, Nov 30, 2018 at 02:35:17PM +0800, Cheng Lin wrote:
> >> If the number of input parameters is less than the total
> >> parameters, an INVAL error will be returned.
> >
> >Do you mean EINVAL?
> >
> Yes, it's EINVAL.

Please adjust the commit log.

> >> This patch ensure no error returned in this condition, just
> >> like other interfaces do.
> >
> >Have an actual example to reproduce?
> >
> >Luis
> >
> We use proc_doulongvec_minmax to pass up to two parameters with kern_table.
> e.g. 
>         {
>                 .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 ~]#

This would be good to have in the commit log as well. But your patch
only addresses one of the proc users, there are a few other checks like
this that would also need to be expanded for this. So please expand
your patch to cover the other cases as well.

Since this worked before I do agree that we need to keep it working now,
and I can't think of an issue with returning 0 now. Since this is about
semantics though I'd like a bit more review from at last one more
person.

Kees, Eric, Andrew?

  Luis

> Cheng
> 
> >> Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>
> >> ---
> >>  kernel/sysctl.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> >> index 5fc724e..9ee261f 100644
> >> --- a/kernel/sysctl.c
> >> +++ b/kernel/sysctl.c
> >> @@ -2779,6 +2779,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
> >>              bool neg;
> >>
> >>              left -= proc_skip_spaces(&p);
> >> +            if (!left)
> >> +                break;
> >>
> >>              err = proc_get_long(&p, &left, &val, &neg,
> >>                           proc_wspace_sep,
> >> --
> >> 1.8.3.1
> >>