linux-kernel - Re: [PATCH v2] powerpc/64: Fix build failure with GCC 8.1

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Date:   Thu, 31 May 2018 21:17:20 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe LEROY <christophe.leroy@....fr>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Geoff Levand <geoff@...radead.org>
Subject: Re: [PATCH v2] powerpc/64: Fix build failure with GCC 8.1

Christophe LEROY <christophe.leroy@....fr> writes:
> Le 31/05/2018 à 07:54, Michael Ellerman a écrit :
>> Christophe LEROY <christophe.leroy@....fr> writes:
>>> Le 29/05/2018 à 11:05, Geert Uytterhoeven a écrit :
>>>> Hi Christophe,
>>>> On Tue, May 29, 2018 at 10:56 AM, Christophe LEROY
>>>> <christophe.leroy@....fr> wrote:
>>>>> Le 29/05/2018 à 09:47, Geert Uytterhoeven a écrit :
>>>>>> On Tue, May 29, 2018 at 8:03 AM, Christophe Leroy
>>>>>>> --- a/arch/powerpc/kernel/nvram_64.c
>>>>>>> +++ b/arch/powerpc/kernel/nvram_64.c
>>>>>>> @@ -1039,7 +1039,7 @@ loff_t __init nvram_create_partition(const char
>>>>>>> *name, int sig,
>>>>>>>            new_part->index = free_part->index;
>>>>>>>            new_part->header.signature = sig;
>>>>>>>            new_part->header.length = size;
>>>>>>> -       strncpy(new_part->header.name, name, 12);
>>>>>>> +       memcpy(new_part->header.name, name, strnlen(name,
>>>>>>> sizeof(new_part->header.name)));
>>>>>>
>>>>>>
>>>>>> The comment for nvram_header.lgnth says:
>>>>>>
>>>>>>            /* Terminating null required only for names < 12 chars. */
>>>>>>
>>>>>> This will not terminate the string with a zero (the struct is
>>>>>> allocated with kmalloc).
>>>>>> So the original code is correct, the new one isn't.
>>>>>
>>>>> Right, then I have to first zeroize the destination.
>>>>
>>>> Using kzalloc() instead of kmalloc() will do.
>>>>
>>>> Still, papering around these warnings seems to obscure things, IMHO.
>>>> And it increases code size, as you had to add a call to strnlen().
>> 
>> 
>> The right fix is to not try and mirror the on-device structure in the
>> kernel struct. We should just use a proper NULL terminated string, which
>> would avoid the need to explicitly do strncmp(.., .., 12) in the code
>> and be less bug prone in general.
>> 
>> The only place where we should need to worry about the 12 byte buffer is
>> in nvram_write_header().
>> 
>> Anyway that's a bigger change, so I'll take this for now with kzalloc().
>
> Thanks. You take it as is and add the kzalloc() or you expect a v3 from 
> me with the kzalloc()

Sorry that wasn't clear was it. I'll add the kzalloc().

cheers