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** Changed in: linux (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1533304
Title:
Kernel Bug: IPv6 Neighbor Discovery
Status in linux package in Ubuntu:
Incomplete
Bug description:
We have discovered what appears to be a bug with the handling of ICMP6
router solicitations on tun interfaces in the Linux kernel. In
particular, if an application is not immediately bound to the tun
interface, router solicitations are never sent out of the interface.
This issue can be replicated easily using the attached scripts.
First, a tun interface is created with permissions for the local user,
sudo is used so the script will prompt for the user password.
$ bash rftun0_create.sh
rftun0 created
16: rftun0: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state DOWN
group default qlen 500
link/none
Then the interface is configured, given an address, and brought "up"
however since there is no application bound to the interface yet there
is no carrier.
$ bash rftun0_up.sh
net.ipv6.conf.rftun0.forwarding = 0
net.ipv6.conf.rftun0.accept_ra = 1
net.ipv6.conf.rftun0.autoconf = 1
net.ipv6.conf.rftun0.accept_ra_rt_info_max_plen = 128
net.ipv6.conf.rftun0.accept_ra_rtr_pref = 1
net.ipv6.conf.rftun0.router_solicitation_delay = 1
net.ipv6.conf.rftun0.router_solicitation_interval = 2
net.ipv6.conf.rftun0.router_solicitations = 200
rftun0 up
16: rftun0: <NO-CARRIER,POINTOPOINT,MULTICAST,NOARP,UP> mtu 1400 qdisc
pfifo_fast state DOWN group default qlen 500
link/none
inet6 fe80::600:4339:125f:760c/64 scope link
valid_lft forever preferred_lft forever
A simple client is then run to bind to the tun interface and read the first
three packets. If things are going well we should see 3 router solicitations,
however we instead see no traffic.
$ python simple_tun_client.py
Timed out...
Timed out...
Timed out...
If we bring the interface down and try again with no delay between
bringing the interface up and binding the application we see things
work as expected.
$ bash rftun0_down.sh
rftun0 down
16: rftun0: <POINTOPOINT,MULTICAST,NOARP> mtu 1400 qdisc pfifo_fast state
DOWN group default qlen 500
link/none
$ bash rftun0_up.sh && python simple_tun_client.py
net.ipv6.conf.rftun0.forwarding = 0
net.ipv6.conf.rftun0.accept_ra = 1
net.ipv6.conf.rftun0.autoconf = 1
net.ipv6.conf.rftun0.accept_ra_rt_info_max_plen = 128
net.ipv6.conf.rftun0.accept_ra_rtr_pref = 1
net.ipv6.conf.rftun0.router_solicitation_delay = 1
net.ipv6.conf.rftun0.router_solicitation_interval = 2
net.ipv6.conf.rftun0.router_solicitations = 200
rftun0 up
16: rftun0: <NO-CARRIER,POINTOPOINT,MULTICAST,NOARP,UP> mtu 1400 qdisc
pfifo_fast state DOWN group default qlen 500
link/none
inet6 fe80::600:1512:6243:38fe/64 scope link
valid_lft forever preferred_lft forever
Read packet from tunnel. 48 bytes.
6000000000083afffe8000000000000006001512624338feff0200000000000000000000000000028500c6e300000000
Read packet from tunnel. 48 bytes.
6000000000083afffe8000000000000006001512624338feff0200000000000000000000000000028500c6e300000000
Read packet from tunnel. 48 bytes.
6000000000083afffe8000000000000006001512624338feff0200000000000000000000000000028500c6e300000000
Furthermore, I can rerun the simple client and continue to receive
router solicitations.
Attempting the same procedure again with a small delay replicates the
original issue. Notice the sleep statement in between the rftun0_up
script and the simple tun client.
$ bash rftun0_down.sh
rftun0 down
16: rftun0: <POINTOPOINT,MULTICAST,NOARP> mtu 1400 qdisc pfifo_fast state
DOWN group default qlen 500
link/none
$ bash rftun0_up.sh && sleep 5 && python simple_tun_client.py
net.ipv6.conf.rftun0.forwarding = 0
net.ipv6.conf.rftun0.accept_ra = 1
net.ipv6.conf.rftun0.autoconf = 1
net.ipv6.conf.rftun0.accept_ra_rt_info_max_plen = 128
net.ipv6.conf.rftun0.accept_ra_rtr_pref = 1
net.ipv6.conf.rftun0.router_solicitation_delay = 1
net.ipv6.conf.rftun0.router_solicitation_interval = 2
net.ipv6.conf.rftun0.router_solicitations = 200
rftun0 up
16: rftun0: <NO-CARRIER,POINTOPOINT,MULTICAST,NOARP,UP> mtu 1400 qdisc
pfifo_fast state DOWN group default qlen 500
link/none
inet6 fe80::600:25f2:67d0:37fc/64 scope link
valid_lft forever preferred_lft forever
Timed out...
Timed out...
Timed out...
This test can be repeated as necessary. On my system, sleep times of
2 seconds or larger seem to always produce the issue, while sleep
times of 1 second seem to work most of the time.
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