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

Message ID ZVPQJIP26dIzRAr6@work
State New
Headers
Series [v2,next] hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_channel() |

Commit Message

Gustavo A. R. Silva Nov. 14, 2023, 7:53 p.m. UTC
  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(-)
  

Comments

Kees Cook Nov. 15, 2023, 3:03 a.m. UTC | #1
On Tue, Nov 14, 2023 at 01:53:08PM -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:
> 
> 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>

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

Reviewed-by: Kees Cook <keescook@chromium.org>
  
Guenter Roeck Nov. 15, 2023, 1:12 p.m. UTC | #2
On Tue, Nov 14, 2023 at 01:53:08PM -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:
> 

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 Nov. 15, 2023, 6:03 p.m. UTC | #3
On 11/15/23 07:12, Guenter Roeck wrote:
> On Tue, Nov 14, 2023 at 01:53:08PM -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:
>>
> 
> 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.

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

Thank you!

--
Gustavo
  

Patch

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;
 }