linux-kernel - Re: [PATCH v2 1/5] hwmon: introduce hwmon_sanitize

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Date:   Wed, 30 Mar 2022 08:23:35 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Xu Yilun <yilun.xu@...el.com>,
        David Laight <David.Laight@...LAB.COM>
Cc:     Michael Walle <michael@...le.cc>, Tom Rix <trix@...hat.com>,
        Jean Delvare <jdelvare@...e.com>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] hwmon: introduce hwmon_sanitize_name()

On 3/30/22 07:51, Xu Yilun wrote:
> On Wed, Mar 30, 2022 at 10:11:39AM +0000, David Laight wrote:
>> From: Xu Yilun
>>> Sent: 30 March 2022 07:51
>>>
>>> On Tue, Mar 29, 2022 at 06:07:26PM +0200, Michael Walle wrote:
>>>> More and more drivers will check for bad characters in the hwmon name
>>>> and all are using the same code snippet. Consolidate that code by adding
>>>> a new hwmon_sanitize_name() function.
>>>>
>>>> Signed-off-by: Michael Walle <michael@...le.cc>
>>>> ---
>>>>   Documentation/hwmon/hwmon-kernel-api.rst |  9 ++++-
>>>>   drivers/hwmon/hwmon.c                    | 49 ++++++++++++++++++++++++
>>>>   include/linux/hwmon.h                    |  3 ++
>>>>   3 files changed, 60 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/hwmon/hwmon-kernel-api.rst b/Documentation/hwmon/hwmon-kernel-api.rst
>>>> index c41eb6108103..12f4a9bcef04 100644
>>>> --- a/Documentation/hwmon/hwmon-kernel-api.rst
>>>> +++ b/Documentation/hwmon/hwmon-kernel-api.rst
>>>> @@ -50,6 +50,10 @@ register/unregister functions::
>>>>
>>>>     void devm_hwmon_device_unregister(struct device *dev);
>>>>
>>>> +  char *hwmon_sanitize_name(const char *name);
>>>> +
>>>> +  char *devm_hwmon_sanitize_name(struct device *dev, const char *name);
>>>> +
>>>>   hwmon_device_register_with_groups registers a hardware monitoring device.
>>>>   The first parameter of this function is a pointer to the parent device.
>>>>   The name parameter is a pointer to the hwmon device name. The registration
>>>> @@ -93,7 +97,10 @@ removal would be too late.
>>>>
>>>>   All supported hwmon device registration functions only accept valid device
>>>>   names. Device names including invalid characters (whitespace, '*', or '-')
>>>> -will be rejected. The 'name' parameter is mandatory.
>>>> +will be rejected. The 'name' parameter is mandatory. Before calling a
>>>> +register function you should either use hwmon_sanitize_name or
>>>> +devm_hwmon_sanitize_name to replace any invalid characters with an
>>>
>>> I suggest                   to duplicate the name and replace ...
>>
>> You are now going to get code that passed in NULL when the kmalloc() fails.
>> If 'sanitizing' the name is the correct thing to do then sanitize it
>> when the copy is made into the allocated structure.
> 
> Then the driver is unaware of the name change, which makes more
> confusing.
> 
>> (I'm assuming that the 'const char *name' parameter doesn't have to
>> be persistent - that would be another bug just waiting to happen.)
> 
> The hwmon core does require a persistent "name" parameter now. No name
> copy is made when hwmon dev register.
> 
>>
>> Seems really pointless to be do a kmalloc() just to pass a string
>> into a function.
> 
> Maybe we should not force a kmalloc() when the sanitizing is needed, let
> the driver decide whether to duplicate the string or not.
> 

Drivers can do that today, and in all existing cases they do so
(which is why I had suggested to handle the duplication in the
convenience function in the first place). Drivers don't _have_
to use the provided convenience functions. At the same time,
convenience functions should cover the most common use cases.

Michael, let's just drop the changes outside drivers/hwmon from
the series, and let's keep hwmon_is_bad_char() in the include file.
Let's just document it, explaining its use case.

Code outside drivers/hwmon can then be independently modified or not
at a later time, based on driver author and/or maintainer preference.

Thanks,
Guenter