Subject: Re: [PATCH 2/3] flex_arrays: allow zero length flex arrays
From: Eric Paris <eparis@redhat.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: steffen.klassert@secunet.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org,
        selinux@tycho.nsa.gov, sds@tycho.nsa.gov
Date: Tue, 26 Apr 2011 16:44:31 -0400
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References: <20110426014531.1740.24077.stgit@paris.rdu.redhat.com>
	 <20110426014537.1740.68472.stgit@paris.rdu.redhat.com>
	 <1303850332.9308.17366.camel@nimitz>
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On Tue, 2011-04-26 at 13:38 -0700, Dave Hansen wrote:
> On Mon, 2011-04-25 at 21:45 -0400, Eric Paris wrote:
> > Just like kmalloc will allow one to allocate a 0 length segment of memory
> > flex arrays should do the same thing.  It should bomb if you try to use
> > something, but it should at least allow the allocation.
> > 
> > Based-on-patch-by: Steffen Klassert <steffen.klassert@secunet.com>
> > Signed-off-by: Eric Paris <eparis@redhat.com>
> > ---
> > 
> >  lib/flex_array.c |   11 ++++++++++-
> >  1 files changed, 10 insertions(+), 1 deletions(-)
> > 
> > diff --git a/lib/flex_array.c b/lib/flex_array.c
> > index 0c33b24..2554a5f 100644
> > --- a/lib/flex_array.c
> > +++ b/lib/flex_array.c
> > @@ -253,9 +253,16 @@ int flex_array_prealloc(struct flex_array *fa, unsigned int start,
> >  	unsigned int end;
> >  	struct flex_array_part *part;
> > 
> > +	if (!fa->total_nr_elements && !start)
> > +		return 0;
> 
> I guess it works either way, but I'd say that checking for a zero 'len'
> prealloc would be more important (and meaningful) than checking a zero
> 'start'.
> 
> If someone passed start=0 and len=44 for a fa->total_nr_elements=0
> array, I'd expect -ENOSPC, but this would return 0.

will fix.

if (!nr_elements && !start)
	return 0;

-Eric

> 
> -- Dave
> 


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