netdev - Re: [PATCH v2] net: ipv6: xfrm6

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Date:   Sat, 10 Mar 2018 19:26:44 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andreas Christoforou <andreaschristofo@...il.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: ipv6: xfrm6_state: remove VLA usage

On Sat, 10 Mar 2018 09:18:46 -0800
Kees Cook <keescook@...omium.org> wrote:

> On Sat, Mar 10, 2018 at 12:43 AM, Stefano Brivio <sbrivio@...hat.com> wrote:
> > On Sat, 10 Mar 2018 09:40:44 +0200
> > Andreas Christoforou <andreaschristofo@...il.com> wrote:
> >  
> >> diff --git a/net/ipv6/xfrm6_state.c b/net/ipv6/xfrm6_state.c
> >> index b15075a..270a53a 100644
> >> --- a/net/ipv6/xfrm6_state.c
> >> +++ b/net/ipv6/xfrm6_state.c
> >> @@ -62,7 +62,7 @@ __xfrm6_sort(void **dst, void **src, int n, int (*cmp)(void *p), int maxclass)
> >>  {
> >>       int i;
> >>       int class[XFRM_MAX_DEPTH];
> >> -     int count[maxclass];
> >> +     int count[XFRM_MAX_DEPTH];
> >>
> >>       memset(count, 0, sizeof(count));  
> >
> > Can you perhaps initialize 'count' instead of calling memset(), now?  
> 
> Do you mean:
> 
> int count[XFRM_MAX_DEPTH] = { };
> 
> instead of the memset()?

Yep.

> I thought the compiler would resolve these both to the same thing?

Yes, for all practical purposes. With gcc 7.3.0 for x86_64, starting
from -O1, it's exactly the same. With e.g. gcc 4.4.7, even with -O3,
they can be a bit different depending on context.

> The former looks better though! :)

Yep! :)

-- 
Stefano