Re: [PATCH v5] sysctl: simplify the min/max boundary check

[Joel Granados]

On Thu, Jan 30, 2025 at 10:32:14PM +0800, Wen Yang wrote:
> 
> 
> On 2025/1/28 01:51, Eric W. Biederman wrote:
> > Joel Granados <joel.granados@xxxxxxxxxx> writes:
> > 
> > > On Thu, Jan 23, 2025 at 12:30:25PM -0600, Eric W. Biederman wrote:
> > > > "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> writes:
> > > > 
> > > > > Joel Granados <joel.granados@xxxxxxxxxx> writes:
> > > > > 
> > > > > > On Sun, Jan 19, 2025 at 10:59:21PM +0800, Wen Yang wrote:
...
> > > struct ctl_table {
> > > 	const char *procname;		/* Text ID for /proc/sys */
> > > 	void *data;
> > > 	int maxlen;
> > > 	umode_t mode;
> > > 	proc_handler *proc_handler;	/* Callback for text formatting */
> > > 	struct ctl_table_poll *poll;
> > >        unsigned long min;
> > >        unsigned long max;
> > > } __randomize_layout;
> > 
> > That is just replace extra1 and extra2 with min and max members.  The
> > members don't have any reason to be pointers.  Without being pointers
> > the min/max functions can just use long values to cap either ints or
> > longs, and there is no room for error.  The integer promotion rules
> > will ensure that even negative values can be stored in unsigned long
> > min and max values successfully.  Plus it is all bog standard C
> > so there is nothing special to learn.
> > 
> > There are a bunch of fiddly little details to transition from where we
> > are today.  The most straightforward way I can see of making the
> > transition is to add the min and max members.  Come up with replacements
> > for proc_doulongvec_minmax and proc_dointvec_minmax that read the new
> > min and max members.  Update all of the users.  Update the few users
> > that use extra1 or extra2 for something besides min and max.  Then
> > remove extra1 and extra2.  At the end it is simpler and requires the
> > same or a little less space.
> > 
> > That was and remains my suggestion.
> > 
> 
> Thanks for your valuable suggestions. We will continue to move forward along
> it and need your more guidance.
> 
> But there are also a few codes that do take the extra{1, 2} as pointers, for
> example:
> 
> int neigh_sysctl_register(struct net_device *dev, struct neigh_parms *p,
>                           proc_handler *handler)
> {
> ...
>         for (i = 0; i < NEIGH_VAR_GC_INTERVAL; i++) {
>                 t->neigh_vars[i].data += (long) p;
>                 t->neigh_vars[i].extra1 = dev;
>                 t->neigh_vars[i].extra2 = p;
>         }
> ...
> }
> 
> static void neigh_proc_update(const struct ctl_table *ctl, int write)
> {
>         struct net_device *dev = ctl->extra1;
>         struct neigh_parms *p = ctl->extra2;
>         struct net *net = neigh_parms_net(p);
>         int index = (int *) ctl->data - p->data;
> ...
> }
Quick question: Do you have a systemic way of identifying these? Do you
have a grep or awk scripts somewhere? I'm actually very interested in
finding out what is the impact of this.

Thx

Best


> 
> 
> So could we modify it in this way to make it compatible with these two
> situations:
> 
> @@ -137,8 +137,16 @@ struct ctl_table {
>         umode_t mode;
>         proc_handler *proc_handler;     /* Callback for text formatting */
>         struct ctl_table_poll *poll;
> -       void *extra1;
> -       void *extra2;
> +       union {
> +               struct {
> +                       void *extra1;
> +                       void *extra2;
> +               };
> +               struct {
> +                       unsigned long min;
> +                       unsigned long max;
> +               };
> +       };
>  } __randomize_layout;
> 
> 
> --
> Best wishes,
> Wen
> 

-- 

Joel Granados