Subject: Re: [PATCH 2/3] flex_arrays: allow zero length flex arrays
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Eric Paris <eparis@redhat.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
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	 <20110426014537.1740.68472.stgit@paris.rdu.redhat.com>
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Date: Tue, 26 Apr 2011 13:38:52 -0700
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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.

-- Dave

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