[PATCH] drm: sysfs: Use scnprintf() for avoiding potential buffer overflow

[Thomas Zimmermann]

Am 11.03.20 um 09:24 schrieb Takashi Iwai:
> On Wed, 11 Mar 2020 09:10:56 +0100,
> Thomas Zimmermann wrote:
>>
>> Hi Takashi
>>
>> Am 11.03.20 um 08:35 schrieb Takashi Iwai:
>>> Since snprintf() returns the would-be-output size instead of the
>>> actual output size, the succeeding calls may go beyond the given
>>> buffer limit.  Fix it by replacing with scnprintf().
>>>
>>> Signed-off-by: Takashi Iwai <tiwai at suse.de>
>>> ---
>>>  drivers/gpu/drm/drm_sysfs.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
>>> index dd2bc85f43cc..9b3180e8c12f 100644
>>> --- a/drivers/gpu/drm/drm_sysfs.c
>>> +++ b/drivers/gpu/drm/drm_sysfs.c
>>> @@ -230,7 +230,7 @@ static ssize_t modes_show(struct device *device,
>>>  
>>>  	mutex_lock(&connector->dev->mode_config.mutex);
>>>  	list_for_each_entry(mode, &connector->modes, head) {
>>> -		written += snprintf(buf + written, PAGE_SIZE - written, "%s\n",
>>> +		written += scnprintf(buf + written, PAGE_SIZE - written, "%s\n",
>>>  				    mode->name);
>>>  	}
>>>  	mutex_unlock(&connector->dev->mode_config.mutex);
>>>
>>
>> In drm_sysfs.c, there are more _show functions with calls to snprintf()
>> that could be replaced by scnprintf(). ATM they don't return the correct
>> length for output that exceeds PAGE_SIZE. since you're at it, you may
>> replace them as well.
> 
> Well, the rest snprintf() calls are single calls and can't be over
> PAGE_SIZE obviously.  IOW, they could be rather replaced with
> sprintf() instead, for a sake of simplicity. 
> 
>> But in any case
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
>>
>> for this patch.
>>
>> Do you want me to merge the patch into drm-misc-next?
> 
> Yes, please.

https://cgit.freedesktop.org/drm/drm-misc/commit/?id=9b9f2219b2c4fa3d1a41245cdc263d09a4c9ad92

Best regards
Thomas

> 
> 
> thanks,
> 
> Takashi
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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