netdev - [6.6.x REGRESSION][BISECTED] dev_snmp6: broken Ip6OutOctets accounting for forwarded IPv6 packets

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Date: Sat, 20 Jan 2024 10:23:18 +0100
From: Vitezslav Samel <vitezslav@...el.cz>
To: Heng Guo <heng.guo@...driver.com>
Cc: netdev@...r.kernel.org
Subject: [6.6.x REGRESSION][BISECTED] dev_snmp6: broken Ip6OutOctets
 accounting for forwarded IPv6 packets

	Hi!

In short:

  since commit e4da8c78973c ("net: ipv4, ipv6: fix IPSTATS_MIB_OUTOCTETS increment duplicated")
the "Ip6OutOctets" entry of /proc/net/dev_snmp6/<interface> isn't
incremented by packet size for outbound forwarded unicast IPv6 packets.


In more detail:

  After move from kernel 6.1.y to 6.6.y I was surprised by very low IPv6 to
IPv4 outgoing traffic ratio counted from /proc/net/... counters on our linux
router. In this simple scenario:

	NET1  <-->  ROUTER  <-->  NET2

  the entry Ip6OutOctets of ROUTER's /proc/net/dev_snmp6/<interface> was
surprisingly low although the IPv6 traffic between NET1 and NET2 is rather
huge comparing to IPv4 traffic. The bisection led me to commit e4da8c78973c.
After reverting it, the numbers went to expected values.

  Numbers for local outbound IPv6 seems correct, as well as numbers for IPv4.

  Since the commit patches both IPv4 and IPv6 reverting it doesn't seem like
the right thing to do. Can you, please, look at it and cook some fix?

	Thanks,

		Vita

#### git bisect log

git bisect start '--' 'include' 'net'
# status: waiting for both good and bad commits
# good: [fb2635ac69abac0060cc2be2873dc4f524f12e66] Linux 6.1.62
git bisect good fb2635ac69abac0060cc2be2873dc4f524f12e66
# status: waiting for bad commit, 1 good commit known
# bad: [5e9df83a705290c4d974693097df1da9cbe25854] Linux 6.6.9
git bisect bad 5e9df83a705290c4d974693097df1da9cbe25854
# good: [830b3c68c1fb1e9176028d02ef86f3cf76aa2476] Linux 6.1
git bisect good 830b3c68c1fb1e9176028d02ef86f3cf76aa2476
# good: [6e98b09da931a00bf4e0477d0fa52748bf28fcce] Merge tag 'net-next-6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next
git bisect good 6e98b09da931a00bf4e0477d0fa52748bf28fcce
# good: [9b39f758974ff8dfa721e68c6cecfd37e6ddb206] Merge tag 'nf-23-07-20' of https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf
git bisect good 9b39f758974ff8dfa721e68c6cecfd37e6ddb206
# good: [38663034491d00652ac599fa48866bcf2ebd7bc1] Merge tag 'fsnotify_for_v6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs
git bisect good 38663034491d00652ac599fa48866bcf2ebd7bc1
# good: [7ba2090ca64ea1aa435744884124387db1fac70f] Merge tag 'ceph-for-6.6-rc1' of https://github.com/ceph/ceph-client
git bisect good 7ba2090ca64ea1aa435744884124387db1fac70f
# bad: [ea1cc20cd4ce55dd920a87a317c43da03ccea192] Merge tag 'v6.6-rc7.vfs.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
git bisect bad ea1cc20cd4ce55dd920a87a317c43da03ccea192
# bad: [b938790e70540bf4f2e653dcd74b232494d06c8f] Bluetooth: hci_codec: Fix leaking content of local_codecs
git bisect bad b938790e70540bf4f2e653dcd74b232494d06c8f
# bad: [6912e724832c47bb381eb1bd1e483ec8df0d0f0f] net/smc: bugfix for smcr v2 server connect success statistic
git bisect bad 6912e724832c47bb381eb1bd1e483ec8df0d0f0f
# bad: [c3b704d4a4a265660e665df51b129e8425216ed1] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU
git bisect bad c3b704d4a4a265660e665df51b129e8425216ed1
# bad: [82ba0ff7bf0483d962e592017bef659ae022d754] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()
git bisect bad 82ba0ff7bf0483d962e592017bef659ae022d754
# bad: [dc9511dd6f37fe803f6b15b61b030728d7057417] sctp: annotate data-races around sk->sk_wmem_queued
git bisect bad dc9511dd6f37fe803f6b15b61b030728d7057417
# good: [7e9be1124dbe7888907e82cab20164578e3f9ab7] netfilter: nf_tables: Audit log setelem reset
git bisect good 7e9be1124dbe7888907e82cab20164578e3f9ab7
# bad: [4e60de1e4769066aa9956c83545c8fa21847f326] Merge tag 'nf-23-08-31' of git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf
git bisect bad 4e60de1e4769066aa9956c83545c8fa21847f326
# bad: [e4da8c78973c1e307c0431e0b99a969ffb8aa3f1] net: ipv4, ipv6: fix IPSTATS_MIB_OUTOCTETS increment duplicated
git bisect bad e4da8c78973c1e307c0431e0b99a969ffb8aa3f1
# first bad commit: [e4da8c78973c1e307c0431e0b99a969ffb8aa3f1] net: ipv4, ipv6: fix IPSTATS_MIB_OUTOCTETS increment duplicated