Re: [GIT PULL net-next 04/17] ndisc: Introduce ndisc_fill_redirect_hdr_option().

[YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>]

Bjørn Mork wrote:
> YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org> writes:
> 
>> Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-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.

I understand your concern.  opt will be disappeared by following
changeset (12 of 17).

--yoshfuji