Re: [PATCH] proc/sysctl: fix return error for proc_doulongvec_minmax

[Kees Cook]

On Thu, Dec 6, 2018 at 12:52 AM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote:
>
> 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@cl150 ~]# echo 1 2 > /proc/sys/kernel/monitor_signals
> > [root@cl150 ~]# cat /proc/sys/kernel/monitor_signals
> > 1       2
> > [root@cl150 ~]# echo 3 > /proc/sys/kernel/monitor_signals
> > -bash: echo: write error: Invalid argument
> > [root@cl150 ~]# echo $?
> > 1
> > [root@cl150 ~]# cat /proc/sys/kernel/monitor_signals
> > 3       2
> > [root@cl150 ~]#
> >
> > 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@cl150 ~]# echo 1 2 > /proc/sys/kernel/monitor_signals
> > [root@cl150 ~]# cat /proc/sys/kernel/monitor_signals
> > 1       2
> > [root@cl150 ~]# echo 3 > /proc/sys/kernel/monitor_signals
> > [root@cl150 ~]# echo $?
> > 0
> > [root@cl150 ~]# cat /proc/sys/kernel/monitor_signals
> > 3       2
> > [root@cl150 ~]#
> >
> > 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@xxxxxxxxxx>
>
> Thanks for fixing up the commit log.
>
> Acked-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

>
> 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



-- 
Kees Cook