Subject: Re: [PATCH] ipv6: fix incorrect ipsec transport mode fragment

From: Gao feng <[email-masked]>
Date: Tue, 15 May 2012 11:44:26 +0800

Hi steffen:

于 2012年05月14日 21:05, Steffen Klassert 写道:
> On Mon, May 14, 2012 at 11:21:00AM +0800, Gao feng wrote:
>> Since commit 299b0767(ipv6: Fix IPsec slowpath fragmentation problem)
>> the fragment of ipsec transport mode packets is incorrect.
>> because tunnel mode needs IPsec headers and trailer for all fragments,
>> while on transport mode it is sufficient to add the headers to the
>> first fragment and the trailer to the last.
> 
> I mentioned this in an other thread some time ago,
> this is due to commit ad0081e43a
> "ipv6: Fragment locally generated tunnel-mode IPSec6 packets as needed"
> changed tunnel mode to do fragmentation before the transformation
> while transport mode still does fragmentation after transformation.
> Now, tunnel mode needs IPsec headers and trailer for all fragments,
> while on transport mode it is sufficient to add the headers to the
> first fragment and the trailer to the last.
> 
>>
>> so modify mtu and maxfraglen base on ipsec mode and if fragment is first
>> or last.
> 
> There might be other opinions, but I don't like to see this IPsec mode
> dependent stuff hacked into the generic ipv6 output path.
> 
> Basically we have two cases. One where we have to add rt->dst.header_len
> to the first fragment and rt->dst.trailer_len to the last fragment,
> and the other where we have to add both to all fragments. So perhaps we
> could isolate this code and create two functions, one for each case.
> 

how about add a function pointer append_data to the struct rt6_info?
so we can just call rt->append_data in ip6_append_data without conside
witch mode it is.

of course, we will set rt->append_data appropriatly in xfrm_lookup.

But the only problem is this will bloats up rt6_info,I don't konw if
it's worth doing it in this way.

> 
>>
>> with my test,it work well and does not trigger slow fragment path.
>>
>> Signed-off-by: Gao feng <[email-masked]>
>> ---
>>  net/ipv6/ip6_output.c |   80 +++++++++++++++++++++++++++++++++++++-----------
>>  1 files changed, 61 insertions(+), 19 deletions(-)
>>
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index b7ca461..9416887 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -1191,19 +1191,23 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
>>  	struct ipv6_pinfo *np = inet6_sk(sk);
>>  	struct inet_cork *cork;
>>  	struct sk_buff *skb;
>> -	unsigned int maxfraglen, fragheaderlen;
>> +	unsigned int maxfraglen, maxfraglen_prev, fragheaderlen;
>>  	int exthdrlen;
>>  	int dst_exthdrlen;
>>  	int hh_len;
>> -	int mtu;
>> +	int mtu, mtu_prev;
>>  	int copy;
>>  	int err;
>>  	int offset = 0;
>>  	int csummode = CHECKSUM_NONE;
>>  	__u8 tx_flags = 0;
>> -
>> +	bool transport_mode = false;
>> +	struct xfrm_state *x = rt->dst.xfrm;
>>  	if (flags&MSG_PROBE)
>>  		return 0;
>> +	if (x && x->props.mode == XFRM_MODE_TRANSPORT)
>> +		transport_mode = true;
>> +
> 
> Btw. beet mode should behave like transport mode here, just tunnel
> mode was changed to do fragmentation before the transformation.
> 

thanks steffen,I miss it and CONFIG_XFRM...