linux-kernel - Re: [PATCH] proc/sysctl: add shared variables for range check

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Date:   Tue, 2 Jul 2019 13:13:48 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Aaron Tomlin <atomlin@...hat.com>
Subject: Re: [PATCH] proc/sysctl: add shared variables for range check

On Tue, 2 Jul 2019 19:21:33 +0200 Matteo Croce <mcroce@...hat.com> wrote:

> On Tue, Jul 2, 2019 at 7:13 PM Alexey Dobriyan <adobriyan@...il.com> wrote:
> >
> > > -static long zero;
> > >  static long long_max = LONG_MAX;
> > >
> > >  struct ctl_table epoll_table[] = {
> > > @@ -301,7 +300,7 @@ struct ctl_table epoll_table[] = {
> > >                 .maxlen         = sizeof(max_user_watches),
> > >                 .mode           = 0644,
> > >                 .proc_handler   = proc_doulongvec_minmax,
> > > -               .extra1         = &zero,
> > > +               .extra1         = SYSCTL_ZERO,
> > >                 .extra2         = &long_max,
> >
> > This looks wrong: proc_doulongvec_minmax() expects "long"s.
> > The whole patch needs rechecking.
> >
> > > +/* shared constants to be used in various sysctls */
> > > +const =======>int<========== sysctl_vals[] = { 0, 1, INT_MAX };
> > > +EXPORT_SYMBOL(sysctl_vals);
> 
> Yes, you're right, that chunk must be dropped.
> Anyway I've checked the patch, this was the only long field touched.

Yup.

akpm3:/usr/src/25> find . -name "*.c" | xargs grep -C4 SYSCTL_ZERO|grep long
./fs/eventpoll.c-               .proc_handler   = proc_doulongvec_minmax,
./fs/eventpoll.c-               .extra2         = &long_max,

I did this:

--- a/fs/eventpoll.c~proc-sysctl-add-shared-variables-for-range-check-fix-4
+++ a/fs/eventpoll.c
@@ -291,6 +291,7 @@ static LIST_HEAD(tfile_check_list);
 
 #include <linux/sysctl.h>
 
+static long long_zero;
 static long long_max = LONG_MAX;
 
 struct ctl_table epoll_table[] = {
@@ -300,7 +301,7 @@ struct ctl_table epoll_table[] = {
 		.maxlen		= sizeof(max_user_watches),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= SYSCTL_ZERO,
+		.extra1		= &long_zero,
 		.extra2		= &long_max,
 	},
 	{ }

I renamed it to avoid using "&zero," in this situation.