Re: [PATCH v2] drivers/iio: Remove all strcpy() uses in favor of strscpy()

[Len Baker]

Hi,

On Mon, Aug 09, 2021 at 10:21:31AM +0100, Jonathan Cameron wrote:
> On Sun, 8 Aug 2021 22:00:34 +0300
> Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
>
> > On Sun, Aug 8, 2021 at 7:25 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> > >
> > > On Sat,  7 Aug 2021 17:22:25 +0200
> > > Len Baker <len.baker@xxxxxxx> wrote:
> > >
> > > > strcpy() performs no bounds checking on the destination buffer. This
> > > > could result in linear overflows beyond the end of the buffer, leading
> > > > to all kinds of misbehaviors. The safe replacement is strscpy().
> > > >
> > > > This patch is an effort to clean up the proliferation of str*()
> > > > functions in the kernel and a previous step in the path to remove
> > > > the strcpy function from the kernel entirely [1].
> > > >
> > > > [1] https://github.com/KSPP/linux/issues/88
> > > >
> > > > Signed-off-by: Len Baker <len.baker@xxxxxxx>
> > > Applied to the togreg branch of iio.git and pushed out as testing
> > > so 0-day can poke at it and see if we missed anything.
> >
> > Isn't it too early? Or am I missing something (see below)?
> >
> > ...
> >
> > > >                       /* use length + 2 for adding minus sign if needed */
> > > > -                     str = devm_kzalloc(regmap_get_device(st->map),
> > > > -                                        strlen(orient) + 2, GFP_KERNEL);
> > > > +                     n = strlen(orient) + 2;
> > > > +                     str = devm_kzalloc(regmap_get_device(st->map), n,
> > > > +                                        GFP_KERNEL);
> > > >                       if (str == NULL)
> > > >                               return -ENOMEM;
> > > >                       if (strcmp(orient, "0") == 0) {
> > > > -                             strcpy(str, orient);
> > > > +                             strscpy(str, orient, n);
> > > >                       } else if (orient[0] == '-') {
> > > > -                             strcpy(str, &orient[1]);
> > > > +                             strscpy(str, &orient[1], n);
> > > >                       } else {
> > > >                               str[0] = '-';
> > > > -                             strcpy(&str[1], orient);
> > > > +                             strscpy(&str[1], orient, n - 1);
> >
> > Why n-1?
>
> n is the total length and this is printing from [1], so n - 1 is remaining
> space.
>
> >
> > > >                       }
> >
> > As far as I understood the logic, it  inverts the sign except the case
> > when it equals 0.
> >
> > I have a question here, why can't we always use +/-?
> > Why can't 0 be prefixed with a sign?
>
> Technically a userspace ABI change, but I agree it should be fairly
> harmless unless someone is rolling their own string handling routines.

I personally don't like the idea of zero having a sign. It's my opinion.
But if you prefer it I have no problem.

> >
> > If the above can be used, we may simplify this code.
> >
> > Len, I think this task may be considered simple, but I recommend
> > thinking about each case and finding a way to simplify it more.
>
Andy, is what I try to do ;) Thanks for the advise.

> It could be a little simpler doing this, so 'maybe' worth doing.

Ok, I will send a new version if there are no objections.

Regards,
Len