Re: [PATCH] PM: QOS: Always use "kstrtos32_from_user()" in cpu_latency_qos_write()

[Xuewen Yan]

Hi rafael

What do you think of this patch？

 # echo 500 > /dev/cpu_dma_latency
[T4893] write: qos value=170930229
[T4893] write: count value=4

the value is 170930229 is because it's hex is 0x0A303035,  It is
exactly the "500\0"

 # echo 200> /dev/cpu_dma_latency
[T4893] write: qos value=170930226
[T4893] write: count value=4

the value is 170930226 is because it's hex is 0x0A303032,  It is
exactly the "200\0"

Thanks!

On Mon, Aug 7, 2023 at 3:17 PM Xuewen Yan <xuewen.yan@xxxxxxxxxx> wrote:
>
> In cpu_latency_qos_write, there is a judgment on whether the count
> value is equal to sizeof(s32). This means that when user write 100~999,
> it would get error value because it would call the "copy_from_user()"
> instead of "kstrtos32".
> Just like:
>
>  # echo 500 > /dev/cpu_dma_latency
> [T4893] write: qos value=170930229
> [T4893] write: count value=4
>
> [T4893] write: qos value=170930226
> [T4893] write: count value=4
>
> To prevent this happening, delete the "copy_from_user()" and
> always use "kstrtos32_from_user()".
>
> Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
> ---
>  kernel/power/qos.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> index 782d3b41c1f3..21a2f873e921 100644
> --- a/kernel/power/qos.c
> +++ b/kernel/power/qos.c
> @@ -379,17 +379,11 @@ static ssize_t cpu_latency_qos_write(struct file *filp, const char __user *buf,
>                                      size_t count, loff_t *f_pos)
>  {
>         s32 value;
> +       int ret;
>
> -       if (count == sizeof(s32)) {
> -               if (copy_from_user(&value, buf, sizeof(s32)))
> -                       return -EFAULT;
> -       } else {
> -               int ret;
> -
> -               ret = kstrtos32_from_user(buf, count, 16, &value);
> -               if (ret)
> -                       return ret;
> -       }
> +       ret = kstrtos32_from_user(buf, count, 16, &value);
> +       if (ret)
> +               return ret;
>
>         cpu_latency_qos_update_request(filp->private_data, value);
>
> --
> 2.25.1
>