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 18:54:18 -0700
From:   Joe Perches <joe@...ches.com>
To:     Richard Narron <comet.berkeley@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] partitions/msdos: FreeBSD UFS2 file systems are
 not recognized

(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.