linux-hardening - Re: [PATCH v4] drivers/iio: Remove all strcpy() uses

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Date:   Sat, 14 Aug 2021 22:36:18 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Len Baker <len.baker@....com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drivers/iio: Remove all strcpy() uses

On Sat, Aug 14, 2021 at 4:55 PM Len Baker <len.baker@....com> 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. So, remove all the uses and add
> devm_kstrdup() or devm_kasprintf() instead.
>
> 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

Thank you very much for doing this!
Now I like the result,
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>

> Signed-off-by: Len Baker <len.baker@....com>
> ---
> The previous versions can be found in:
>
> v1
> https://lore.kernel.org/linux-hardening/20210801171157.17858-1-len.baker@gmx.com/
>
> v2
> https://lore.kernel.org/linux-hardening/20210807152225.9403-1-len.baker@gmx.com/
>
> v3
> https://lore.kernel.org/linux-hardening/20210814090618.8920-1-len.baker@gmx.com/
>
> Changelog v1 -> v2
> - Modify the commit changelog to inform that the motivation of this
>   patch is to remove the strcpy() function from the kernel entirely
>   (Jonathan Cameron).
>
> Changelog v2 -> v3
> - Rewrite the code using devm_kstrdup() and devm_kasprintf() functions
>   (Andy Shevchenko).
> - Rebase against v5.14-rc5.
>
> Changelog v3 -> v4
> - Reorder the variables (Andy Shevchenko).
> - Get the device in the definition block (Andy Shevchenko).
> - Reword the comment (Andy Shevchenko).
> - Change the conditions in the "if" statement to clarify the "0" check
>   (Andy Shevchenko).
>
>  drivers/iio/imu/inv_mpu6050/inv_mpu_magn.c | 30 +++++++++++++---------
>  1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_magn.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_magn.c
> index f282e9cc34c5..7eceae0012c9 100644
> --- a/drivers/iio/imu/inv_mpu6050/inv_mpu_magn.c
> +++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_magn.c
> @@ -261,6 +261,7 @@ int inv_mpu_magn_set_rate(const struct inv_mpu6050_state *st, int fifo_rate)
>   */
>  int inv_mpu_magn_set_orient(struct inv_mpu6050_state *st)
>  {
> +       struct device *dev = regmap_get_device(st->map);
>         const char *orient;
>         char *str;
>         int i;
> @@ -281,19 +282,24 @@ int inv_mpu_magn_set_orient(struct inv_mpu6050_state *st)
>                 /* z <- -z */
>                 for (i = 0; i < 3; ++i) {
>                         orient = st->orientation.rotation[6 + i];
> -                       /* use length + 2 for adding minus sign if needed */
> -                       str = devm_kzalloc(regmap_get_device(st->map),
> -                                          strlen(orient) + 2, GFP_KERNEL);
> -                       if (str == NULL)
> +
> +                       /*
> +                        * The value is negated according to one of the following
> +                        * rules:
> +                        *
> +                        * 1) Drop leading minus.
> +                        * 2) Leave 0 as is.
> +                        * 3) Add leading minus.
> +                        */
> +                       if (orient[0] == '-')
> +                               str = devm_kstrdup(dev, orient + 1, GFP_KERNEL);
> +                       else if (orient[0] == '0' && orient[1] == '\0')
> +                               str = devm_kstrdup(dev, orient, GFP_KERNEL);
> +                       else
> +                               str = devm_kasprintf(dev, GFP_KERNEL, "-%s", orient);
> +                       if (!str)
>                                 return -ENOMEM;
> -                       if (strcmp(orient, "0") == 0) {
> -                               strcpy(str, orient);
> -                       } else if (orient[0] == '-') {
> -                               strcpy(str, &orient[1]);
> -                       } else {
> -                               str[0] = '-';
> -                               strcpy(&str[1], orient);
> -                       }
> +
>                         st->magn_orient.rotation[6 + i] = str;
>                 }
>                 break;
> --
> 2.25.1
>


-- 
With Best Regards,
Andy Shevchenko