Hi,
I am Vijay Tandeker working in TejasNetworks Bangalore, which works
in a telecommunication domain. I have one query regarding
IP_MULTICAST_LOOP option.
My configuration:
Kernel version: 2.6.32
One OSPF routing protocol deamon is running in my system. It has opened
one raw socket with
- IP_HDRINCL option set to 1
- IP_MULTICAST_LOOP option set to 0
IP fragmentation logic is implemented in my application. Means if OSPF
tries to send any packet which exceeds MTU of the transmitting
interface, it fragments it and gives to the kernel using sendmsg(). In
my case, I am getting all my fragmented packets back to the application
(which should not happen if IP_MULTICAST_LOOP option is set to zero).
Following are my observations:
1) In ip_mc_output() function inside "net/ipv4/ip_output.c" file:
/*
* Multicasts are looped back for other local users
*/
if (rt->rt_flags&RTCF_MULTICAST) {
if ((!sk || inet_sk(sk)->mc_loop)
#ifdef CONFIG_IP_MROUTE
/* Small optimization: do not loopback not local frames,
which returned after forwarding; they will be dropped
by ip_mr_input in any case.
Note, that local frames are looped back to be delivered
to local recipients.
This check is duplicated in ip_mr_input at the moment.
*/
&& ((rt->rt_flags&RTCF_LOCAL) || !(IPCB(skb)->flags&IPSKB_FORWARDED))
#endif
) {
}
Here sk(or skb->sk) pointer is NULL and "((rt->rt_flags&RTCF_LOCAL) ||
!(IPCB(skb)->flags&IPSKB_FORWARDED))" condition is True. Because of this
I am getting all my fragmented packets looped back to application.
2) On further debugging I found that:
In nf_ct_ipv4_gather_frags() function inside
"ipv4/netfilter/nf_defrag_ipv4.c" file
- skb_orphan(skb); is being called, which is setting skb->sk to NULL.
- No call to restore skb->sk back to some valid value later on.
My questions:-
- Is this done intentionally ?
- If No, please suggest the solution to restore skb->sk pointer.
- If Yes, please suggest the solution to restore skb->sk pointer.
Kindly let me know in case if the problem is not clear or you need any
more data.
Thanks & Regards,
Vijay
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