linux-kernel - Re: [PATCH] sysctl: handle table->maxlen properly for proc

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Date:   Thu, 19 May 2022 22:10:54 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        Muchun Song <smuchun@...il.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
Subject: Re: [PATCH] sysctl: handle table->maxlen properly for proc_dobool

On Thu, May 19, 2022 at 9:09 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Thu, May 19, 2022 at 08:55:05PM +0800, Muchun Song wrote:
> > @@ -428,6 +428,8 @@ static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp,
> >                               int write, void *data)
> >  {
> >       if (write) {
> > +             if (*negp || (*lvalp != 0 && *lvalp != 1))
> > +                     return -EINVAL;
> >               *(bool *)valp = *lvalp;
> >       } else {
> >               int val = *(bool *)valp;
>
> Is this the right approach?  Or should we do as C does and interpret
> writing non-zero as true?  ie:

All right. We could obey the C rule here.

>
>                 *(bool *)valp = (bool)*lvalp;
>
> (is that cast needed?  It wouldn't be if it were an int, but bool is a
> bit weird)
>

If the cast is weird. How about:

        *(bool *)valp = *lvalp ? true : false;

Thanks.