linux-kernel - Re: [PATCH v2] net: ipv6: xfrm6

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Date:   Mon, 12 Mar 2018 13:24:03 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Stefano Brivio <sbrivio@...hat.com>
CC:     Kees Cook <keescook@...omium.org>,
        Andreas Christoforou <andreaschristofo@...il.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.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, Mar 10, 2018 at 07:26:44PM +0100, Stefano Brivio wrote:
> 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! :)

If Andreas does a v3 anyway, please also consider to trim the subject
line to something like:

xfrm: remove VLA usage in __xfrm6_sort()