Messages in this thread | | | From | Eric Dumazet <> | Date | Fri, 29 Apr 2022 15:05:23 -0700 | Subject | Re: Routing loops & TTL tracking with tunnel devices |
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On Fri, Apr 29, 2022 at 2:54 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > Hi Eric, > > On Fri, Apr 29, 2022 at 11:14 PM Eric Dumazet <eric.dumazet@gmail.com> wrote: > > > > > > On 4/29/22 14:07, Jason A. Donenfeld wrote: > > > > Hi Eric, > > > > On Fri, Apr 29, 2022 at 01:54:27PM -0700, Eric Dumazet wrote: > > > > Anyway, it'd be nice if there were a free u8 somewhere in sk_buff that I > > could use for tracking times through the stack. Other kernels have this > > but afaict Linux still does not. I looked into trying to overload some > > existing fields -- tstamp/skb_mstamp_ns or queue_mapping -- which I was > > thinking might be totally unused on TX? > > > > if skbs are stored in some internal wireguard queue, can not you use > > skb->cb[], > > > > like many other layers do ? > > > > This isn't for some internal wireguard queue. The packets get sent out > > of udp_tunnel_xmit_skb(), so they leave wireguard's queues. > > > > > > OK, where is the queue then ? > > > > dev_xmit_recursion() is supposed to catch long chains of virtual devices. > > This is the long-chain-of-virtual-devices case indeed. But > dev_xmit_recursion() does not help here, since that's just a per-cpu > increment, assuming that the packet actually gets xmit'd in its > ndo_start_xmit function. But in reality, wireguard queues up the > packet, encrypts it in some worker later, and eventually transmits it > with udp_tunnel_xmit_skb(). All the while ndo_start_xmit() has long > returned. So no help from dev_xmit_recursion(). >
I assume you add encap headers to the skb ?
You could check if the wireguard header is there already, or if the amount of headers is crazy.
net/core/flow_dissector.c might help.
You also can take a look at CONFIG_SKB_EXTENSIONS infrastructure.
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