linux-kernel - Re: [PATCH v3 1/1] partitions/msdos: FreeBSD UFS2 file systems are not recognized

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Date:   Fri, 26 May 2017 20:20:47 -0700 (PDT)
From:   Richard Narron <comet.berkeley@...il.com>
To:     Joe Perches <joe@...ches.com>
cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] partitions/msdos: FreeBSD UFS2 file systems are
 not recognized

On Fri, 26 May 2017, Joe Perches wrote:

> (please keep replies on the list)
>
> On Fri, 2017-05-26 at 18:33 -0700, Richard Narron wrote:
>> On Fri, 26 May 2017, Joe Perches wrote:
>>> On Fri, 2017-05-26 at 16:30 -0700, Richard Narron wrote:
>>>> On Fri, 26 May 2017, Joe Perches wrote:
>>>>> On Fri, 2017-05-26 at 03:48 -0700, Richard Narron wrote:
>>>>>> The code in block/partitions/msdos.c recognizes FreeBSD, OpenBSD
>>>>>> and NetBSD partitions and does a reasonable job picking out OpenBSD
>>>>>> and NetBSD UFS subpartitions.
>>>>>>
>>>>>> But for FreeBSD the subpartitions are always "bad".
>>>>>>
>>>>>>      Kernel: <bsd:bad subpartition - ignored
>>>>>
>>>>> []
>>>>>>   block/partitions/msdos.c | 2 ++
>>>>>
>>>>> []
>>>>>> @@ -300,6 +300,8 @@ static void parse_bsd(struct parsed_part
>>>>>>   			continue;
>>>>>>   		bsd_start = le32_to_cpu(p->p_offset);
>>>>>>   		bsd_size = le32_to_cpu(p->p_size);
>>>>>> +		if (memcmp(flavour, "bsd\0", 4) == 0)
>>>>>
>>>>> Weird code.  Why not:
>>>>>
>>>>> 		if (strcmp(flavor, "bsd") == 0)
>>>>>
>>>>
>>>> I instinctively trust the memcmp function as it seems more like
>>>> assembly language to me and more straight forward and more reliable than
>>>> strcmp.
>>>
>>> That really doesn't matter.
>>>
>>> Your code stores "bsd\0\0" and not just "bsd\0"
>>>
>>
>> Thanks for looking at this code. I do appreciate it.
>>
>> How about saving a byte and doing this instead?
>>
>>            if (memcmp(flavour, "bsd", 4) == 0)
>>
>> I do appreciate your input as coding style is important, but so too is
>> reliability.
>>
>> I don't trust the string functions and probably never will.
>>
>> It is not surprising to me that things like SQL injection and any number of other
>> C string exploits are very common.
>>
>> IBM gave up on the idea of marking memory to keep track of data length with the 1401 machines in the 1950's.
>>
>> But Digital Equipment kept the idea alive of using null characters for a
>> long time.  Sadly the C programming language copied this bad idea for
>> strings.
>
> Let's not argue the language.
>
> Please use what's normal for the language as that is
> readers of the code typically expect.
>

Under the /block/partitions directory the c programs have about 13 uses 
of memcmp() and 6 uses of strcmp().