On Wed, 2017-11-01 at 18:00 -0700, Eric Dumazet wrote: > On Wed, 2017-11-01 at 17:10 -0700, Christoph Paasch wrote: > > > Yes, that looks good to me. Thanks! > > > > But we still need to clean up the skb in tcp_v4_send_reset and > > tcp_v4_send_ack, as the fields (e.g., tcp_skb_cb->seq) have been set when > > coming from tcp_v4_rcv. > > You might be confused : ip_send_unicast_reply() does not send back the > incoming skb. > > A fresh skb is allocated, then appended/sent. > > And commit 24a2d43d8886f5a29c did the changes to provide to > __ip_options_echo() the proper IPCB header location. >
More details : Fields written by tcp_init_nondata_skb() on the synack packet : ->seq (32bits) at offset 0 of skb->cb[] ->end_seq (32bits) at offset 4 of skb->cb[] ->tcp_gso_segs (16bits) at offset 8 ->tcp_flags (8bits) at offset 12 value (TCPHDR_SYN | TCPHDR_ACK -> 0x12) ->sacked (8bits) at offset 13 IPCB fields sharing these 14 bytes : iif /* 32bits, offset 0 */ opt.faddr (32bits) offset 4 opt.nexthop (32bits) offset 8 /* value 1 */ opt.optlen (8bits) offset 12 /* value 0x12 */ opt.srr (8bits) offset 13 IP6CB fields sharing these 14 bytes : iif /* 32bits, offset 0 */ ra /* 16 bits, offset 4 */ dst0 /* 16 bits offset 6 */ srcrt /* 16 bits offset 8 */ -> 0x0001 dst1 /* 16 bits offset 10 */ (not mangled -> 0) lastopt /* 16 bits offset 12 */ -> 0x12 At xmit : IPV4 uses ip_build_and_send_pkt() to transmit the SYNACK, so skb->cb[] is not used. IPv6 uses other fields. So I really wonder what exact issue you observed, please share your drugs ;) Thanks !
