On Mon, Nov 13, 2023 at 01:38:12PM -0600, Gustavo A. R. Silva wrote:
> Based on the documentation below, the maximum number of Fan tach
> channels is 16:
>
> Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt:45:
> 45 - aspeed,fan-tach-ch : should specify the Fan tach input channel.
> 46 integer value in the range 0 through 15, with 0 indicating
> 47 Fan tach channel 0 and 15 indicating Fan tach channel 15.
> 48 At least one Fan tach input channel is required.
>
> However, the compiler doesn't know that, and legitimaly warns about a potential
> overwrite in array `u8 fan_tach_ch_source[16]` in `struct aspeed_pwm_tacho_data`,
> in case `index` takes a value outside the boundaries of the array:
>
All that doesn't warrant introducing checkpatch warnings.
> drivers/hwmon/aspeed-pwm-tacho.c:
> 179 struct aspeed_pwm_tacho_data {
> ...
> 184 bool fan_tach_present[16];
> ...
> 193 u8 fan_tach_ch_source[16];
> ...
> 196 };
>
> In function ‘aspeed_create_fan_tach_channel’,
> inlined from ‘aspeed_create_fan’ at drivers/hwmon/aspeed-pwm-tacho.c:877:2,
> inlined from ‘aspeed_pwm_tacho_probe’ at drivers/hwmon/aspeed-pwm-tacho.c:936:9:
> drivers/hwmon/aspeed-pwm-tacho.c:751:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
> 751 | priv->fan_tach_ch_source[index] = pwm_source;
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
> drivers/hwmon/aspeed-pwm-tacho.c: In function ‘aspeed_pwm_tacho_probe’:
> drivers/hwmon/aspeed-pwm-tacho.c:193:12: note: at offset [48, 255] into destination object ‘fan_tach_ch_source’ of size 16
> 193 | u8 fan_tach_ch_source[16];
> | ^~~~~~~~~~~~~~~~~~
>
> Fix this by sanity checking `index` before using it to index arrays of
> size 16 elements in `struct aspeed_pwm_tacho_data`. Also, and just for
> completeness, add a `pr_err()` message to display in the unlikely case
> `0 > index >= 16`.
>
> This is probably the last remaining -Wstringop-overflow issue in the
> kernel, and this patch helps with the ongoing efforts to enable such
> compiler option globally.
>
I am sorry, but this description almost completely misses the point.
The real issue is that the values in aspeed,fan-tach-ch are not range
checked, which can cause real problems if is elements are set to values
larger than 15. This is a real problem and has nothing to do with string
overflows.
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> drivers/hwmon/aspeed-pwm-tacho.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hwmon/aspeed-pwm-tacho.c b/drivers/hwmon/aspeed-pwm-tacho.c
> index 997df4b40509..092a81916325 100644
> --- a/drivers/hwmon/aspeed-pwm-tacho.c
> +++ b/drivers/hwmon/aspeed-pwm-tacho.c
> @@ -166,6 +166,8 @@
>
> #define MAX_CDEV_NAME_LEN 16
>
> +#define MAX_ASPEED_FAN_TACH_CHANNELS 16
> +
> struct aspeed_cooling_device {
> char name[16];
> struct aspeed_pwm_tacho_data *priv;
> @@ -181,7 +183,7 @@ struct aspeed_pwm_tacho_data {
> struct reset_control *rst;
> unsigned long clk_freq;
> bool pwm_present[8];
> - bool fan_tach_present[16];
> + bool fan_tach_present[MAX_ASPEED_FAN_TACH_CHANNELS];
> u8 type_pwm_clock_unit[3];
> u8 type_pwm_clock_division_h[3];
> u8 type_pwm_clock_division_l[3];
> @@ -190,7 +192,7 @@ struct aspeed_pwm_tacho_data {
> u16 type_fan_tach_unit[3];
> u8 pwm_port_type[8];
> u8 pwm_port_fan_ctrl[8];
> - u8 fan_tach_ch_source[16];
> + u8 fan_tach_ch_source[MAX_ASPEED_FAN_TACH_CHANNELS];
> struct aspeed_cooling_device *cdev[8];
> const struct attribute_group *groups[3];
> };
> @@ -746,10 +748,14 @@ static void aspeed_create_fan_tach_channel(struct aspeed_pwm_tacho_data *priv,
>
> for (val = 0; val < count; val++) {
> index = fan_tach_ch[val];
> - aspeed_set_fan_tach_ch_enable(priv->regmap, index, true);
> - priv->fan_tach_present[index] = true;
> - priv->fan_tach_ch_source[index] = pwm_source;
> - aspeed_set_fan_tach_ch_source(priv->regmap, index, pwm_source);
> + if (index < MAX_ASPEED_FAN_TACH_CHANNELS) {
> + aspeed_set_fan_tach_ch_enable(priv->regmap, index, true);
> + priv->fan_tach_present[index] = true;
> + priv->fan_tach_ch_source[index] = pwm_source;
> + aspeed_set_fan_tach_ch_source(priv->regmap, index, pwm_source);
> + } else {
> + pr_err("Invalid Fan Tach input channel %u\n.", index);
This should use dev_err() (and, yes, that means dev needs to be passed
as argument), and the function should return -EINVAL if this is
encountered. Also, error handling should come first.
if (index >= MAX_ASPEED_FAN_TACH_CHANNELS) {
dev_err(dev, "Invalid Fan Tach input channel %u\n.", index);
return -EINVAL;
}
Thanks,
Guenter
