staging: rtl8192e: Fix divide fault when calculating beacon age

Message ID 20221103200507.14304-1-Larry.Finger@lwfinger.net
State New
Headers
Series staging: rtl8192e: Fix divide fault when calculating beacon age |

Commit Message

Larry Finger Nov. 3, 2022, 8:05 p.m. UTC
  When the configuration parameter CONFIG_HZ is less that 100, the compiler
generates an error as follows:

../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtl819x_translate_scan':
../drivers/staging/rtl8192e/rtllib_wx.c:220:57: warning: division by zero [-Wdiv-by-zero]
  220 |                       (jiffies - network->last_scanned) / (HZ / 100));
      |                                                         ^
In file included from ../include/linux/skbuff.h:45,
                 from ../include/linux/if_ether.h:19,
                 from ../include/linux/etherdevice.h:20,
                 from ../drivers/staging/rtl8192e/rtllib_wx.c:18:
../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtllib_wx_get_scan':
../drivers/staging/rtl8192e/rtllib_wx.c:261:70: warning: division by zero [-Wdiv-by-zero]
  261 |                                    (jiffies - network->last_scanned) /
      |

In fact, is HZ is not a multiple of 100, the calculation will be wrong, but it
will compile correctly.

The fix is to get rid of the (HZ / 100) portion. To decrease any round-off
errors, the compiler is forced to perform the 100 * jiffies-difference before
dividing by HX. This patch is only compile tested.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
---
 drivers/staging/rtl8192e/rtllib_wx.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
  

Comments

Philipp Hortmann Nov. 3, 2022, 10:01 p.m. UTC | #1
On 11/3/22 21:05, Larry Finger wrote:
> When the configuration parameter CONFIG_HZ is less that 100, the compiler
> generates an error as follows:
> 
> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtl819x_translate_scan':
> ../drivers/staging/rtl8192e/rtllib_wx.c:220:57: warning: division by zero [-Wdiv-by-zero]
>    220 |                       (jiffies - network->last_scanned) / (HZ / 100));
>        |                                                         ^
> In file included from ../include/linux/skbuff.h:45,
>                   from ../include/linux/if_ether.h:19,
>                   from ../include/linux/etherdevice.h:20,
>                   from ../drivers/staging/rtl8192e/rtllib_wx.c:18:
> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtllib_wx_get_scan':
> ../drivers/staging/rtl8192e/rtllib_wx.c:261:70: warning: division by zero [-Wdiv-by-zero]
>    261 |                                    (jiffies - network->last_scanned) /
>        |
> 
> In fact, is HZ is not a multiple of 100, the calculation will be wrong, but it
> will compile correctly.
> 
> The fix is to get rid of the (HZ / 100) portion. To decrease any round-off
> errors, the compiler is forced to perform the 100 * jiffies-difference before
> dividing by HX. This patch is only compile tested.
> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
> ---
>   drivers/staging/rtl8192e/rtllib_wx.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c
> index da2c41c9b92f..7013425102dd 100644
> --- a/drivers/staging/rtl8192e/rtllib_wx.c
> +++ b/drivers/staging/rtl8192e/rtllib_wx.c
> @@ -217,7 +217,7 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
>   	p = custom;
>   	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
>   		      " Last beacon: %lums ago",
> -		      (jiffies - network->last_scanned) / (HZ / 100));
> +		      (100 *(jiffies - network->last_scanned)) / HZ);
>   	iwe.u.data.length = p - custom;
>   	if (iwe.u.data.length)
>   		start = iwe_stream_add_point_rsl(info, start, stop,
> @@ -258,8 +258,8 @@ int rtllib_wx_get_scan(struct rtllib_device *ieee,
>   				   escape_essid(network->ssid,
>   						network->ssid_len),
>   				   network->bssid,
> -				   (jiffies - network->last_scanned) /
> -				   (HZ / 100));
> +				   (100 * (jiffies - network->last_scanned)) /
> +				   HZ);
>   	}
>   
>   	spin_unlock_irqrestore(&ieee->lock, flags);

Line length of the description is to long.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
  
Randy Dunlap Nov. 3, 2022, 11:08 p.m. UTC | #2
On 11/3/22 13:05, Larry Finger wrote:
> When the configuration parameter CONFIG_HZ is less that 100, the compiler
> generates an error as follows:
> 
> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtl819x_translate_scan':
> ../drivers/staging/rtl8192e/rtllib_wx.c:220:57: warning: division by zero [-Wdiv-by-zero]
>   220 |                       (jiffies - network->last_scanned) / (HZ / 100));
>       |                                                         ^
> In file included from ../include/linux/skbuff.h:45,
>                  from ../include/linux/if_ether.h:19,
>                  from ../include/linux/etherdevice.h:20,
>                  from ../drivers/staging/rtl8192e/rtllib_wx.c:18:
> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtllib_wx_get_scan':
> ../drivers/staging/rtl8192e/rtllib_wx.c:261:70: warning: division by zero [-Wdiv-by-zero]
>   261 |                                    (jiffies - network->last_scanned) /
>       |
> 
> In fact, is HZ is not a multiple of 100, the calculation will be wrong, but it
> will compile correctly.
> 
> The fix is to get rid of the (HZ / 100) portion. To decrease any round-off
> errors, the compiler is forced to perform the 100 * jiffies-difference before
> dividing by HX. This patch is only compile tested.

              HZ.

> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested

Thanks.

> ---
>  drivers/staging/rtl8192e/rtllib_wx.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c
> index da2c41c9b92f..7013425102dd 100644
> --- a/drivers/staging/rtl8192e/rtllib_wx.c
> +++ b/drivers/staging/rtl8192e/rtllib_wx.c
> @@ -217,7 +217,7 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
>  	p = custom;
>  	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
>  		      " Last beacon: %lums ago",
> -		      (jiffies - network->last_scanned) / (HZ / 100));
> +		      (100 *(jiffies - network->last_scanned)) / HZ);

                      (100 * (jiffies ...

>  	iwe.u.data.length = p - custom;
>  	if (iwe.u.data.length)
>  		start = iwe_stream_add_point_rsl(info, start, stop,
> @@ -258,8 +258,8 @@ int rtllib_wx_get_scan(struct rtllib_device *ieee,
>  				   escape_essid(network->ssid,
>  						network->ssid_len),
>  				   network->bssid,
> -				   (jiffies - network->last_scanned) /
> -				   (HZ / 100));
> +				   (100 * (jiffies - network->last_scanned)) /
> +				   HZ);
>  	}
>  
>  	spin_unlock_irqrestore(&ieee->lock, flags);
  
Larry Finger Nov. 4, 2022, 1:28 a.m. UTC | #3
On 11/3/22 17:01, Philipp Hortmann wrote:
> On 11/3/22 21:05, Larry Finger wrote:
>> When the configuration parameter CONFIG_HZ is less that 100, the compiler
>> generates an error as follows:
>>
>> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtl819x_translate_scan':
>> ../drivers/staging/rtl8192e/rtllib_wx.c:220:57: warning: division by zero 
>> [-Wdiv-by-zero]
>>    220 |                       (jiffies - network->last_scanned) / (HZ / 100));
>>        |                                                         ^
>> In file included from ../include/linux/skbuff.h:45,
>>                   from ../include/linux/if_ether.h:19,
>>                   from ../include/linux/etherdevice.h:20,
>>                   from ../drivers/staging/rtl8192e/rtllib_wx.c:18:
>> ../drivers/staging/rtl8192e/rtllib_wx.c: In function 'rtllib_wx_get_scan':
>> ../drivers/staging/rtl8192e/rtllib_wx.c:261:70: warning: division by zero 
>> [-Wdiv-by-zero]
>>    261 |                                    (jiffies - network->last_scanned) /
>>        |
>>
>> In fact, is HZ is not a multiple of 100, the calculation will be wrong, but it
>> will compile correctly.
>>
>> The fix is to get rid of the (HZ / 100) portion. To decrease any round-off
>> errors, the compiler is forced to perform the 100 * jiffies-difference before
>> dividing by HX. This patch is only compile tested.
>>
>> Reported-by: Randy Dunlap <rdunlap@infradead.org>
>> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
>> ---
>>   drivers/staging/rtl8192e/rtllib_wx.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/staging/rtl8192e/rtllib_wx.c 
>> b/drivers/staging/rtl8192e/rtllib_wx.c
>> index da2c41c9b92f..7013425102dd 100644
>> --- a/drivers/staging/rtl8192e/rtllib_wx.c
>> +++ b/drivers/staging/rtl8192e/rtllib_wx.c
>> @@ -217,7 +217,7 @@ static inline char *rtl819x_translate_scan(struct 
>> rtllib_device *ieee,
>>       p = custom;
>>       p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
>>                 " Last beacon: %lums ago",
>> -              (jiffies - network->last_scanned) / (HZ / 100));
>> +              (100 *(jiffies - network->last_scanned)) / HZ);
>>       iwe.u.data.length = p - custom;
>>       if (iwe.u.data.length)
>>           start = iwe_stream_add_point_rsl(info, start, stop,
>> @@ -258,8 +258,8 @@ int rtllib_wx_get_scan(struct rtllib_device *ieee,
>>                      escape_essid(network->ssid,
>>                           network->ssid_len),
>>                      network->bssid,
>> -                   (jiffies - network->last_scanned) /
>> -                   (HZ / 100));
>> +                   (100 * (jiffies - network->last_scanned)) /
>> +                   HZ);
>>       }
>>       spin_unlock_irqrestore(&ieee->lock, flags);
> 
> Line length of the description is to long.

Addressed in v2.

Larry
  

Patch

diff --git a/drivers/staging/rtl8192e/rtllib_wx.c b/drivers/staging/rtl8192e/rtllib_wx.c
index da2c41c9b92f..7013425102dd 100644
--- a/drivers/staging/rtl8192e/rtllib_wx.c
+++ b/drivers/staging/rtl8192e/rtllib_wx.c
@@ -217,7 +217,7 @@  static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
 	p = custom;
 	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
 		      " Last beacon: %lums ago",
-		      (jiffies - network->last_scanned) / (HZ / 100));
+		      (100 *(jiffies - network->last_scanned)) / HZ);
 	iwe.u.data.length = p - custom;
 	if (iwe.u.data.length)
 		start = iwe_stream_add_point_rsl(info, start, stop,
@@ -258,8 +258,8 @@  int rtllib_wx_get_scan(struct rtllib_device *ieee,
 				   escape_essid(network->ssid,
 						network->ssid_len),
 				   network->bssid,
-				   (jiffies - network->last_scanned) /
-				   (HZ / 100));
+				   (100 * (jiffies - network->last_scanned)) /
+				   HZ);
 	}
 
 	spin_unlock_irqrestore(&ieee->lock, flags);