linux-kernel - Re: [PATCH] hwmon: (ibmpowernv) refactor deprecated strncpy

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Message-ID: <4b490305-0ab7-403f-7bec-a08fb8f20b56@roeck-us.net>
Date:   Thu, 14 Sep 2023 22:40:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Kees Cook <keescook@...omium.org>,
        Justin Stitt <justinstitt@...gle.com>
Cc:     Jean Delvare <jdelvare@...e.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-hwmon@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] hwmon: (ibmpowernv) refactor deprecated strncpy

On 9/14/23 22:24, Kees Cook wrote:
> On Thu, Sep 14, 2023 at 11:21:06PM +0000, Justin Stitt wrote:
>> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
>>
>> We should prefer more robust and less ambiguous string interfaces.
>>
>> A suitable replacement is `strscpy` [2] due to the fact that it
>> guarantees NUL-termination on the destination buffer without
>> unnecessarily NUL-padding since `buf` is already zero-initialized.
>>
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
>> Link: https://github.com/KSPP/linux/issues/90
>> Cc: linux-hardening@...r.kernel.org
>> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
>> ---
>>   drivers/hwmon/ibmpowernv.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/hwmon/ibmpowernv.c b/drivers/hwmon/ibmpowernv.c
>> index 594254d6a72d..57d829dbcda6 100644
>> --- a/drivers/hwmon/ibmpowernv.c
>> +++ b/drivers/hwmon/ibmpowernv.c
>> @@ -234,7 +234,7 @@ static int get_sensor_index_attr(const char *name, u32 *index, char *attr)
>>   	if (copy_len >= sizeof(buf))
>>   		return -EINVAL;
>>   
>> -	strncpy(buf, hash_pos + 1, copy_len);
>> +	strscpy(buf, hash_pos + 1, copy_len);
> 
> This is another case of precise byte copying -- this just needs to be
> memcpy. Otherwise this truncates the trailing character. Imagine a name
> input of "fan#2-data". "buf" wants to get "2". copy_len is 1, and
> strscpy would eat it. :)
> 

It is really sad that the submitters of such "cleanup" patches can't be bothered
to check what they are doing. They can't even be bothered to write a coccinelle
script that would avoid pitfalls like this one, and they expect others to do their
homework for them.

And then people wonder why there is maintainer burnout. I am so tired of that.

Guenter