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Since commitfac6fce9bd("net: icmp6: provide input address for traceroute6") ICMPv6 errors have source addresses from the ingress interface. However, this overrides when source address selection is influenced by setting preferred source addresses on routes. This can result in ICMP errors being lost to upstream BCP38 filters when the wrong source addresses are used, breaking path MTU discovery and traceroute. This patch sets the modified source address selection to only take place when the route used has no prefsrc set. It can be tested with: ip link add v1 type veth peer name v2 ip netns add test ip netns exec test ip link set lo up ip link set v2 netns test ip link set v1 up ip netns exec test ip link set v2 up ip addr add 2001:db8::1/64 dev v1 nodad ip addr add 2001:db8::3 dev v1 nodad ip netns exec test ip addr add 2001:db8::2/64 dev v2 nodad ip netns exec test ip route add unreachable 2001:db8:1::1 ip netns exec test ip addr add 2001:db8:100::1 dev lo ip netns exec test ip route add 2001:db8::1 dev v2 src 2001:db8:100::1 ip route add 2001:db8:1000::1 via 2001:db8::2 traceroute6 -s 2001:db8::1 2001:db8:1000::1 traceroute6 -s 2001:db8::3 2001:db8:1000::1 ip netns delete test Output before: $ traceroute6 -s 2001:db8::1 2001:db8:1000::1 traceroute to 2001:db8:1000::1 (2001:db8:1000::1), 30 hops max, 80 byte packets 1 2001:db8::2 (2001:db8::2) 0.843 ms !N 0.396 ms !N 0.257 ms !N $ traceroute6 -s 2001:db8::3 2001:db8:1000::1 traceroute to 2001:db8:1000::1 (2001:db8:1000::1), 30 hops max, 80 byte packets 1 2001:db8::2 (2001:db8::2) 0.772 ms !N 0.257 ms !N 0.357 ms !N After: $ traceroute6 -s 2001:db8::1 2001:db8:1000::1 traceroute to 2001:db8:1000::1 (2001:db8:1000::1), 30 hops max, 80 byte packets 1 2001:db8:100::1 (2001:db8:100::1) 8.885 ms !N 0.310 ms !N 0.174 ms !N $ traceroute6 -s 2001:db8::3 2001:db8:1000::1 traceroute to 2001:db8:1000::1 (2001:db8:1000::1), 30 hops max, 80 byte packets 1 2001:db8::2 (2001:db8::2) 1.403 ms !N 0.205 ms !N 0.313 ms !N Fixes:fac6fce9bd("net: icmp6: provide input address for traceroute6") Signed-off-by: Tim Stallard <code@timstallard.me.uk> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.