Re: [PATCH] thermal: sysfs: Use sysfs_emit_at() in trans_table_show()

[Rafael J. Wysocki (Intel)]

On Sun, Jul 19, 2026 at 3:23 PM Thorsten Blum <thorsten.blum@xxxxxxxxx> wrote:
>
> Replace snprintf() with sysfs_emit_at() in trans_table_show().
> sysfs_emit_at() is preferred for formatting sysfs output because it
> provides safer bounds checking.
>
> Convert multiple PAGE_SIZE length checks to check the number of bytes
> actually copied by sysfs_emit_at(), thus avoiding manual buffer size
> accounting.
>
> Consistently return -EFBIG when the transition table output exceeds the
> sysfs buffer, including the header row.
>
> Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
> ---
>  drivers/thermal/thermal_sysfs.c | 49 ++++++++++++++++-----------------
>  1 file changed, 24 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index b44abfc997ed..adbcb2c011e8 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -706,7 +706,7 @@ static ssize_t trans_table_show(struct device *dev,
>         struct thermal_cooling_device *cdev = to_cooling_device(dev);
>         struct cooling_dev_stats *stats;
>         ssize_t len = 0;
> -       int i, j;
> +       int i, j, copied;
>
>         guard(cooling_dev)(cdev);
>
> @@ -714,41 +714,40 @@ static ssize_t trans_table_show(struct device *dev,
>         if (!stats)
>                 return -ENODATA;
>
> -       len += snprintf(buf + len, PAGE_SIZE - len, " From  :    To\n");
> -       len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
> +       len += sysfs_emit_at(buf, len, " From  :    To\n");
> +       len += sysfs_emit_at(buf, len, "       : ");
>         for (i = 0; i <= cdev->max_state; i++) {
> -               if (len >= PAGE_SIZE)
> -                       break;
> -               len += snprintf(buf + len, PAGE_SIZE - len, "state%2u  ", i);
> +               copied = sysfs_emit_at(buf, len, "state%2u  ", i);
> +               if (!copied)
> +                       goto buf_full;
> +               len += copied;
>         }
> -       if (len >= PAGE_SIZE)
> -               return PAGE_SIZE;
> -
> -       len += snprintf(buf + len, PAGE_SIZE - len, "\n");
> +       len += sysfs_emit_at(buf, len, "\n");
>
>         for (i = 0; i <= cdev->max_state; i++) {
> -               if (len >= PAGE_SIZE)
> -                       break;
> -
> -               len += snprintf(buf + len, PAGE_SIZE - len, "state%2u:", i);
> +               copied = sysfs_emit_at(buf, len, "state%2u:", i);
> +               if (!copied)
> +                       goto buf_full;
> +               len += copied;
>
>                 for (j = 0; j <= cdev->max_state; j++) {
> -                       if (len >= PAGE_SIZE)
> -                               break;
> -                       len += snprintf(buf + len, PAGE_SIZE - len, "%8u ",
> +                       copied = sysfs_emit_at(buf, len, "%8u ",
>                                 stats->trans_table[i * (cdev->max_state + 1) + j]);
> +                       if (!copied)
> +                               goto buf_full;
> +                       len += copied;
>                 }
> -               if (len >= PAGE_SIZE)
> -                       break;
> -               len += snprintf(buf + len, PAGE_SIZE - len, "\n");
> -       }
> -
> -       if (len >= PAGE_SIZE) {
> -               pr_warn_once("Thermal transition table exceeds PAGE_SIZE. Disabling\n");
> -               len = -EFBIG;
> +               copied = sysfs_emit_at(buf, len, "\n");
> +               if (!copied)
> +                       goto buf_full;
> +               len += copied;
>         }
>
>         return len;
> +
> +buf_full:
> +       pr_warn_once("Thermal transition table exceeds PAGE_SIZE. Disabling\n");
> +       return -EFBIG;
>  }
>
>  static DEVICE_ATTR_RO(total_trans);

Applied as 7.3 material, thanks!