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

From: David Laight
Date: Tue Aug 10 2021 - 04:30:36 EST


From: Jonathan Cameron
> Sent: 09 August 2021 10:22
>
> 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.

If you do:
/* negate 'orient' */
n = strlen(orient) + 1;
str = malloc(n + 1);
if (n == 2 && orient[0] == '0')
memcpy(str, orient, n);
else if (orient[0] == '-')
memcpy(str, orient + 1, n - 1);
else {
str[0] = '-';
memcpy(str + 1, orient, n);
}
Then it is probably less confusing.

David

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