Re: [PATCH] vti4: Fix a ipip packet processing bug in 'IPCOMP' virtual tunnel

["Su Yanjun <suyj.fnst@cn.fujitsu.com>" <suyj.fnst@cn.fujitsu.com>]

On 1/4/2019 3:43 PM, Steffen Klassert wrote:

> On Thu, Jan 03, 2019 at 07:48:41AM -0500, Su Yanjun wrote:
>> Recently we run a network test over ipcomp virtual tunnel.We find that
>> if a ipv4 packet needs fragment, then the peer can't receive
>> it.
>>
>> We deep into the code and find that when packet need fragment the smaller
>> fragment will be encapsulated by ipip not ipcomp. So when the ipip packet
>> goes into xfrm, it's skb->dev is not properly set. The ipv4 reassembly code
>> always set skb'dev to the last fragment's dev. After ipv4 defrag processing,
>> when the kernel rp_filter parameter is set, the skb will be drop by -EXDEV
>> error.
> Why not just leaving rp_filter disabled or in 'loose mode' if you use ipcomp?
In my option rp_filter should not affect the ip_vti functionality.
The root cause is the origin tunnel code doesn't update skb->dev.
vti only cares about ipcomp, esp, ah packets.
>> This patch adds compatible support for the ipip process in ipcomp virtual tunnel.
>>
>> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
>> ---
>>   net/ipv4/ip_vti.c | 25 ++++++++++++++++++++++++-
>>   1 file changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
>> index de31b30..63de2f6 100644
>> --- a/net/ipv4/ip_vti.c
>> +++ b/net/ipv4/ip_vti.c
>> @@ -65,6 +65,9 @@ static int vti_input(struct sk_buff *skb, int nexthdr, __be32 spi,
>>   
>>   		XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4 = tunnel;
>>   
>> +		if (iph->protocol == IPPROTO_IPIP)
>> +			skb->dev = tunnel->dev;
>> +
>>   		return xfrm_input(skb, nexthdr, spi, encap_type);
>>   	}
>>   
>> @@ -76,10 +79,15 @@ static int vti_input(struct sk_buff *skb, int nexthdr, __be32 spi,
>>   
>>   static int vti_rcv(struct sk_buff *skb)
>>   {
>> +	__be32 spi = 0;
>> +	
>>   	XFRM_SPI_SKB_CB(skb)->family = AF_INET;
>>   	XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct iphdr, daddr);
>> +	
>> +	if (ip_hdr(skb)->protocol == IPPROTO_IPIP)
>> +		spi = ip_hdr(skb)->saddr;
>>   
>> -	return vti_input(skb, ip_hdr(skb)->protocol, 0, 0);
>> +	return vti_input(skb, ip_hdr(skb)->protocol, spi, 0);
> You use the src address as spi, how is this supposed to work?
>
This code derives from xfrm4_tunnel and i just want the vti can handle 
ipip packet as xfrm4 tunnel does.


Thanks,
Su