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

[Steffen Klassert]

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?

> 
> This patch adds compatible support for the ipip process in ipcomp virtual tunnel.
> 
> Signed-off-by: Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>
> ---
>  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?