On Thu, Sep 18, 2014 at 04:54:53PM +0100, Simon Vincent wrote: > It looks like in 6lowpan_iphc.c lowpan_header_compress the original ipv6 > header is removed and the compressed header is attached. > > These four lines are responsible. > skb_pull(skb, sizeof(struct ipv6hdr)); > skb_reset_transport_header(skb); > memcpy(skb_push(skb, hc06_ptr - head), head, hc06_ptr - head); > skb_reset_network_header(skb); > > I don't think we can do this as the skb is being used in other parts of the > ip stack. Hence when the ipv6 header is read elsewhere the addresses become > corrupt as they have been overwritten by the 6lowpan compressed header. > > Any ideas on how to fix this? > yes, but I don't believe that this makes trouble. <--- or only makes trouble by replacing data, see below. It's called by a callback of header_ops [0]. This is for generating the mac header with address information from neighbor discovery cache (mainly destination address) and source addresse (mainly netdev->dev_addr). Another example of this function is ethernet. [1] On [1] you will se that the ethernet header will created there. - Get data from skb for ethhdr (ethernet header) struct ethhdr *eth = (struct ethhdr *)skb_push(skb, ETH_HLEN); - memcpy(eth->h_source, saddr, ETH_ALEN); <-- source address - memcpy(eth->h_dest, daddr, ETH_ALEN); <-- destination address. So they using the callback there to manipulate the skb here. Another idea is that, maybe we can ADD data but not REPLACING existing data with that. I don't know right now. But I moved this handling out of the create callback of header_ops. This also fix the issue by running wireshark&co on a lowpan interface. What I did is only to save the address information in the reserved room of skb in this callback. [2] Then running replacing header in the xmit callback of lowpan device. It looks very different now! I have also splitted the lowpan implementation in three files "main.c, tx.c, rx.c". Please note that. This code is part of the rework and I want to fix the wireshark&co issue there. I don't have a solution for this right now which applies on current mainline, sorry! But the xmit callback is 100% secure by replacing skb header data. If you like you can try to apply it on mainline. What I said is that this also fix the IPv6 capturing on a lowpan interface. I want also say to you that I added a comment there "TODO ask david or marc if this run into trouble", because I am not sure if the reserved skb room can be overwritten sometimes, then we stuck into the same issue. (Worked on my side currently), but I also don't do much raw socket RPL messages. ;-) What I know is that we can't use skb->cb here to save the information, this would be overwritten by traffic control. - Alex [0] http://lxr.free-electrons.com/source/include/linux/netdevice.h#L255 [1] http://lxr.free-electrons.com/source/net/ethernet/eth.c#L78 [2] https://github.com/linux-wpan/linux-wpan-next/blob/7ccf5a24a19a72b857bbcbc76342f4838dd85d6b/net/ieee802154/6lowpan/tx.c#L59 [3] https://github.com/linux-wpan/linux-wpan-next/blob/7ccf5a24a19a72b857bbcbc76342f4838dd85d6b/net/ieee802154/6lowpan/tx.c#L261 -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
