netdev - Re: [GIT PULL net-next 04/17] ndisc: Introduce ndisc_fill_redirect_hdr

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Date:	Wed, 19 Dec 2012 12:47:33 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [GIT PULL net-next 04/17] ndisc: Introduce ndisc_fill_redirect_hdr_option().

YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org> writes:

> Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> ---
>  net/ipv6/ndisc.c |   21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index a181113..0a4f3a9 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1332,6 +1332,19 @@ static void ndisc_redirect_rcv(struct sk_buff *skb)
>  	icmpv6_notify(skb, NDISC_REDIRECT, 0, 0);
>  }
>  
> +static u8 *ndisc_fill_redirect_hdr_option(u8 *opt, struct sk_buff *orig_skb,
> +					  int rd_len)
> +{
> +	memset(opt, 0, 8);
> +	*(opt++) = ND_OPT_REDIRECT_HDR;
> +	*(opt++) = (rd_len >> 3);
> +	opt += 6;
> +
> +	memcpy(opt, ipv6_hdr(orig_skb), rd_len - 8);
> +
> +	return opt;
> +}
> +

I realize that it doesn't currently matter, but the above modification
of "opt" looks like a bug-waiting-to-happen to me.

>  void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target)
>  {
>  	struct net_device *dev = skb->dev;
> @@ -1461,12 +1474,8 @@ void ndisc_send_redirect(struct sk_buff *skb, const struct in6_addr *target)
>  	 *	build redirect option and copy skb over to the new packet.
>  	 */
>  
> -	memset(opt, 0, 8);
> -	*(opt++) = ND_OPT_REDIRECT_HDR;
> -	*(opt++) = (rd_len >> 3);
> -	opt += 6;
> -
> -	memcpy(opt, ipv6_hdr(skb), rd_len - 8);
> +	if (rd_len)
> +		opt = ndisc_fill_redirect_hdr_option(opt, skb, rd_len);


I understand that opt isn't currently used after this, but if it ever is
then it is going to come as big a surprise that this implies opt += 8;

This was previously quite clear when the code was inline, but it becomes
problematic when it is factored out.


Bjørn
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