public inbox for netdev@vger.kernel.org
 help / color / mirror / Atom feed
From: "Linus Lüssing" <linus.luessing@c0d3.blue>
To: Eric Dumazet <edumazet@google.com>
Cc: netdev@vger.kernel.org, netfilter@vger.kernel.org
Subject: skb->mark not cleared for MLDv2 Reports? (skb->mark == 212 / 0xd4)
Date: Mon, 17 Jul 2023 13:22:03 +0200	[thread overview]
Message-ID: <ZLUkWyFiwEqi721V@sellars> (raw)

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
]
$ 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

             reply	other threads:[~2023-07-17 11:30 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-17 11:22 Linus Lüssing [this message]
2023-07-20 20:05 ` skb->mark not cleared for MLDv2 Reports? (skb->mark == 212 / 0xd4) Kuniyuki Iwashima

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ZLUkWyFiwEqi721V@sellars \
    --to=linus.luessing@c0d3.blue \
    --cc=edumazet@google.com \
    --cc=netdev@vger.kernel.org \
    --cc=netfilter@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox