Re: [PATCH v5 01/11] driver: platform: Add helper for safer setting of driver_override

On Wed, Mar 16, 2022 at 5:06 PM Krzysztof Kozlowski krzysztof.kozlowski@canonical.com wrote:

...

+int driver_set_override(struct device *dev, const char **override,

•                   const char *s, size_t len)
  

+{

•   const char *new, *old;
  

•   char *cp;
  

•   if (!dev || !override || !s)
  

•           return -EINVAL;
  

Sorry, I didn't pay much attention on this. First of all, I would drop dev checks and simply require that dev should be valid. Do you expect this can be called when dev is invalid? I would like to hear if it's anything but theoretical. Second one, is the !s requirement. Do I understand correctly that the string must be always present? But then how we NULify the override? Is it possible? Third one is absence of len check. See below.

•   /*
  

•    * The stored value will be used in sysfs show callback (sysfs_emit()),
  

•    * which has a length limit of PAGE_SIZE and adds a trailing newline.
  

•    * Thus we can store one character less to avoid truncation during sysfs
  

•    * show.
  

•    */
  

•   if (len >= (PAGE_SIZE - 1))
  

•           return -EINVAL;
  

I would relax this to make sure we can use it if \n is within this limit.

•   cp = strnchr(s, len, '\n');
  

•   if (cp)
  

•           len = cp - s;
  

•   new = kstrndup(s, len, GFP_KERNEL);
  

Here is a word about the len check.

•   if (!new)
  

If len == 0, this won't trigger and you have something very interesting as a result.

One way is to use ZERO_PTR_OR_NULL() another is explicitly check for 0 and issue a (different?) error code.

•           return -ENOMEM;
  

•   device_lock(dev);
  

•   old = *override;
  

•   if (cp != s) {
  

•           *override = new;
  

•   } else {
  

•           kfree(new);
  

•           *override = NULL;
  

•   }
  

•   device_unlock(dev);
  

•   kfree(old);
  

•   return 0;
  

+}