Re: [PATCH v2] drivers/iio: Remove all strcpy() uses in favor of strscpy()
From: Jonathan Cameron
Date: Mon Aug 09 2021 - 05:22:06 EST
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.
>
> 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.
>
It could be a little simpler doing this, so 'maybe' worth doing.
Jonathan