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Message-ID: <20231008005922.24777-1-heng.guo@windriver.com>
Date: Sun, 8 Oct 2023 08:59:21 +0800
From: Heng Guo <heng.guo@...driver.com>
To: <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
<kuba@...nel.org>, <pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <filip.pudak@...driver.com>,
<heng.guo@...driver.com>
Subject: [PATCH 0/1] Issue description and debug
Hi maintainers,
The IPSTATS_MIB_OUTFORWDATAGRAMS is counted after fragment check.
Reproduce environment:
network with 3 VM linuxs is connected as below:
VM1<---->VM2(latest kernel 6.5.0-rc7)<---->VM3
VM1: eth0 ip: 192.168.122.207 MTU 1800
VM2: eth0 ip: 192.168.122.208, eth1 ip: 192.168.123.224 MTU 1500
VM3: eth0 ip: 192.168.123.240 MTU 1800
Reproduce:
VM1 send 1600 bytes UDP data to VM3 using tools scapy with flags='DF'.
scapy command:
send(IP(dst="192.168.123.240",flags='DF')/UDP()/str('0'*1600),count=1,
inter=1.000000)
Result:
Before IP data is sent.
----------------------------------------------------------------------
root@...ux86-64:~# cat /proc/net/snmp
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors
ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests
OutDiscards OutNoRoutes ReasmTimeout ReasmReqdss
Ip: 1 64 6 0 2 2 0 0 2 4 0 0 0 0 0 0 0 0 0
......
root@...ux86-64:~#
----------------------------------------------------------------------
After IP data is sent.
----------------------------------------------------------------------
root@...ux86-64:~# cat /proc/net/snmp
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors
ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests
OutDiscards OutNoRoutes ReasmTimeout ReasmReqdss
Ip: 1 64 7 0 2 2 0 0 2 5 0 0 0 0 0 0 0 1 0
......
root@...ux86-64:~#
----------------------------------------------------------------------
ForwDatagrams is always keeping 2 without increment.
Issue description and patch:
ip_exceeds_mtu() in ip_forward() drops this IP datagram because skb len
(1600 sending by scapy) is over MTU(1500 in VM2) and "DF" is set.
According to RFC 4293 "3.2.3. IP Statistics Tables",
+-------+------>------+----->-----+----->-----+
| InForwDatagrams (6) | OutForwDatagrams (6) |
| V +->-+ OutFragReqds
| InNoRoutes | | (packets)
/ (local packet (3) | |
| IF is that of the address | +--> OutFragFails
| and may not be the receiving IF) | | (packets)
the IPSTATS_MIB_OUTFORWDATAGRAMS should be counted before fragment
check.
The existing implementation, instead, would incease the counter after
fragment check: ip_exceeds_mtu() in ipv4 and ip6_pkt_too_big() in ipv6.
So do patch to move IPSTATS_MIB_OUTFORWDATAGRAMS counter to ip_forward()
for ipv4 and ip6_forward() for ipv6.
Test result with patch:
Before IP data is sent.
----------------------------------------------------------------------
root@...ux86-64:~# cat /proc/net/snmp
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors
ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests
OutDiscards OutNoRoutes ReasmTimeout ReasmReqdss
Ip: 1 64 6 0 2 2 0 0 2 4 0 0 0 0 0 0 0 0 0
......
root@...ux86-64:~#
----------------------------------------------------------------------
After IP data is sent.
----------------------------------------------------------------------
root@...ux86-64:~# cat /proc/net/snmp
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors
ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests
OutDiscards OutNoRoutes ReasmTimeout ReasmReqdss
Ip: 1 64 7 0 2 3 0 0 2 5 0 0 0 0 0 0 0 1 0
......
root@...ux86-64:~#
----------------------------------------------------------------------
ForwDatagrams is updated from 2 to 3.
Thanks,
Heng
This is a new email thread, last one is:
https://lore.kernel.org/all/20230914051623.2180843-2-heng.guo@windriver.com
Heng Guo (1):
net-next: fix IPSTATS_MIB_OUTFORWDATAGRAMS increment after fragment
check
net/ipv4/ip_forward.c | 4 ++--
net/ipv6/ip6_output.c | 6 ++----
2 files changed, 4 insertions(+), 6 deletions(-)
--
2.25.1
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