linux-kernel - Re: [PATCH v3 ipsec-next] xfrm: remove VLA usage in __xfrm6

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Date:   Wed, 25 Apr 2018 11:11:47 +0200
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andreas Christoforou <andreaschristofo@...il.com>,
        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>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 ipsec-next] xfrm: remove VLA usage in __xfrm6_sort()

Hi Kees,

On Tue, 24 Apr 2018 16:46:51 -0700
Kees Cook <keescook@...omium.org> wrote:

> In the quest to remove all stack VLA usage removed from the kernel[1],
> just use XFRM_MAX_DEPTH as already done for the "class" array. In one
> case, it'll do this loop up to 5, the other caller up to 6.
> 
> [1] https://lkml.org/lkml/2018/3/7/621
> 
> Co-developed-by: Andreas Christoforou <andreaschristofo@...il.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v3:
> - adjust Subject and commit log (Steffen)
> - use "= { }" instead of memset() (Stefano)
> - reorder variables (Stefano)
> v2:
> - use XFRM_MAX_DEPTH for "count" array (Steffen and Mathias).
> ---
>  net/ipv6/xfrm6_state.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/xfrm6_state.c b/net/ipv6/xfrm6_state.c
> index 16f434791763..eeb44b64ae7f 100644
> --- a/net/ipv6/xfrm6_state.c
> +++ b/net/ipv6/xfrm6_state.c
> @@ -60,9 +60,9 @@ xfrm6_init_temprop(struct xfrm_state *x, const struct xfrm_tmpl *tmpl,
>  static int
>  __xfrm6_sort(void **dst, void **src, int n, int (*cmp)(void *p), int maxclass)
>  {
> -	int i;
> +	int count[XFRM_MAX_DEPTH] = { };
>  	int class[XFRM_MAX_DEPTH];
> -	int count[maxclass];
> +	int i;
>  
>  	memset(count, 0, sizeof(count));

I guess you forgot to remove the memset() here. Just to be clear, I
think this is how it should look like:

--- a/net/ipv6/xfrm6_state.c
+++ b/net/ipv6/xfrm6_state.c
@@ -60,11 +60,9 @@ xfrm6_init_temprop(struct xfrm_state *x, const struct xfrm_tmpl *tmpl,
 static int
 __xfrm6_sort(void **dst, void **src, int n, int (*cmp)(void *p), int maxclass)
 {
-       int i;
+       int count[XFRM_MAX_DEPTH] = { };
        int class[XFRM_MAX_DEPTH];
-       int count[maxclass];
-
-       memset(count, 0, sizeof(count));
+       int i;
 
        for (i = 0; i < n; i++) {
                int c;

-- 
Stefano