[PATCH v2][next] hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_channel()

Gustavo A. R. Silva
2023-11-14T19:53:19Z

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:

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, pass `dev` as
argument to function `aspeed_create_fan_tach_channel()`, and add an error
message in case `index` is out-of-bounds, in which case return `-EINVAL`.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
- Pass `dev` to function aspeed_create_fan_tach_channel() and return
-EINVAL in case of error. (Guenter)
- Update changelog text.

v1:
- Link: https://lore.kernel.org/linux-hardening/ZVJ7JBFoULzY3VGx@work/

drivers/hwmon/aspeed-pwm-tacho.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/aspeed-pwm-tacho.c b/drivers/hwmon/aspeed-pwm-tacho.c
index 997df4b40509..9a209e064e46 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];
};
@@ -737,7 +739,8 @@ static void aspeed_create_pwm_port(struct aspeed_pwm_tacho_data *priv,
aspeed_set_pwm_port_fan_ctrl(priv, pwm_port, INIT_FAN_CTRL);
}

-static void aspeed_create_fan_tach_channel(struct aspeed_pwm_tacho_data *priv,
+static int aspeed_create_fan_tach_channel(struct device *dev,
+ struct aspeed_pwm_tacho_data *priv,
u8 *fan_tach_ch,
int count,
u8 pwm_source)
@@ -746,11 +749,17 @@ static void aspeed_create_fan_tach_channel(struct aspeed_pwm_tacho_data *priv,

for (val = 0; val < count; val++) {
index = fan_tach_ch[val];
+ if (index >= MAX_ASPEED_FAN_TACH_CHANNELS) {
+ dev_err(dev, "Invalid Fan Tach input channel %u\n.", index);
+ return -EINVAL;
+ }
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);
}
+
+ return 0;
}

static int
@@ -874,7 +883,10 @@ static int aspeed_create_fan(struct device *dev,
fan_tach_ch, count);
if (ret)
return ret;
- aspeed_create_fan_tach_channel(priv, fan_tach_ch, count, pwm_port);
+
+ ret = aspeed_create_fan_tach_channel(dev, priv, fan_tach_ch, count, pwm_port);
+ if (ret)
+ return ret;

return 0;
}
--
2.34.1