hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_channel()

PATCH In review Gustavo A. R. Silva 4 participants 4 messages Nov 14, 2023 – Nov 15, 2023

Subsystems (2)

Hardware monitoring Arm/Aspeed machine support

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Gustavo A. R. Silva

author

2023-11-14 19:53 UTC #0 lore raw

PATCH v2 1/1 hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_channel()

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 <[email protected]>

---
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 at work/

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

drivers/hwmon/aspeed-pwm-tacho.c +16 -4

index 997df4b40509..9a209e064e46 100644
@@ -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;
 }

Signature · 1 line

2.34.1

Kees Cook

Reviewed-by on v2 1/1

2023-11-15 03:03 UTC #1 lore raw

Quoted 32 lines · Gustavo A. R. Silva

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];
      |            ^~~~~~~~~~~~~~~~~~

Quoted 6 lines

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 <[email protected]>

Thanks for the v2! This looks good; it's able to pass back the error now.

Reviewed-by Kees Cook <[email protected]>

Signature · 1 line

Kees Cook

Guenter Roeck

maintainer

2023-11-15 13:12 UTC #2 lore raw

In reply to Gustavo A. R. Silva

Quoted 5 lines · Gustavo A. R. Silva

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.

Quoted 8 lines

 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:

Still messes the point. This isn't about "the compiler doesn't know that", it is a real bug which may result in out-of-bounds accesses.

Oh, never mind, I'll just apply it.

Guenter

Gustavo A. R. Silva

2023-11-15 18:03 UTC #3 lore raw

Quoted 10 lines · Guenter Roeck

Quoted 9 lines · Gustavo A. R. Silva
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.

Quoted 7 lines

Quoted 4 lines
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:
Still messes the point. This isn't about "the compiler doesn't know that", it is a real bug which may result in out-of-bounds accesses.

Oh, I mentioned that in anticipation of people saying something in the tone of 'that's never going to happen.' :p

However, if this is a real bug, it should probably be tagged for -stable.

Quoted 2 lines

Oh, never mind, I'll just apply it.

Thank you!

--
Gustavo