From: Linus =?utf-8?Q?L=C3=BCssing?= <linus.luessing@xxxxxxxxx> Date: Mon, 17 Jul 2023 13:22:03 +0200 > Hi, > > I noticed that MLDv2 Reports don't seem to have a default > skb->mark of 0. Instead it is 212 / 0xd4 for me: > > ``` > $ ip link add dummy0 type dummy > $ ip link set up dummy0 arp on > $ ip6tables -I INPUT -i dummy0 -j LOG --log-ip-options > [ send an MLDv2 Query, for instance via the ipv6toolkit > https://github.com/T-X/ipv6toolkit/tree/pr-mldq6-mldv2 I haven't looked yet though, a complete repro would make us debug it easier. (Same for MLDv1) Thanks! > ] > $ dmesg > ... > [38336.524879] IN= OUT=dummy0 SRC=fe80:0000:0000:0000:1c01:1cff:fec1:5669 DST=ff02:0000:0000:0000:0000:0000:0000:0016 LEN=76 TC=0 HOPLIMIT=1 FLOWLBL=0 OPT ( ) PROTO=ICMPv6 TYPE=143 CODE=0 MARK=0xd4 > ... > ``` > > For MLDv1 Reports I don't see this issue, there it's always > 0 by default. > > I'm wondering if this 212 value comes from the > skb->reserved_tailroom (formerly avail_size) which the skb->mark > is unioned with? Am I reading > a21d45726a ("tcp: avoid order-1 allocations on wifi and tx path") > correctly that the IPv6 stack should have reset skb->mark to 0 > before transmission? > > Initially observed on a Linux 5.10.184. But I can reproduce > this on a Linux 6.3.7, too. > > Regards, Linus
