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f6071e5e39
Currently rp_filter tests in fib_tests.sh:fib_rp_filter_test() are
failing. ping sockets are bound to dummy1 using the "-I" option
(SO_BINDTODEVICE), but socket lookup is failing when receiving ping
replies, since the routing table thinks they belong to dummy0.
For example, suppose ping is using a SOCK_RAW socket for ICMP messages.
When receiving ping replies, in __raw_v4_lookup(), sk->sk_bound_dev_if
is 3 (dummy1), but dif (skb_rtable(skb)->rt_iif) says 2 (dummy0), so the
raw_sk_bound_dev_eq() check fails. Similar things happen in
ping_lookup() for SOCK_DGRAM sockets.
These tests used to pass due to a bug [1] in iputils, where "ping -I"
actually did not bind ICMP message sockets to device. The bug has been
fixed by iputils commit f455fee41c07 ("ping: also bind the ICMP socket
to the specific device") in 2016, which is why our rp_filter tests
started to fail. See [2] .
Fixing the tests while keeping everything in one netns turns out to be
nontrivial. Rework the tests and build the following topology:
┌─────────────────────────────┐ ┌─────────────────────────────┐
│ network namespace 1 (ns1) │ │ network namespace 2 (ns2) │
│ │ │ │
│ ┌────┐ ┌─────┐ │ │ ┌─────┐ ┌────┐ │
│ │ lo │<───>│veth1│<────────┼────┼─>│veth2│<──────────>│ lo │ │
│ └────┘ ├─────┴──────┐ │ │ ├─────┴──────┐ └────┘ │
│ │192.0.2.1/24│ │ │ │192.0.2.1/24│ │
│ └────────────┘ │ │ └────────────┘ │
└─────────────────────────────┘ └─────────────────────────────┘
Consider sending an ICMP_ECHO packet A in ns2. Both source and
destination IP addresses are 192.0.2.1, and we use strict mode rp_filter
in both ns1 and ns2:
1. A is routed to lo since its destination IP address is one of ns2's
local addresses (veth2);
2. A is redirected from lo's egress to veth2's egress using mirred;
3. A arrives at veth1's ingress in ns1;
4. A is redirected from veth1's ingress to lo's ingress, again, using
mirred;
5. In __fib_validate_source(), fib_info_nh_uses_dev() returns false,
since A was received on lo, but reverse path lookup says veth1;
6. However A is not dropped since we have relaxed this check for lo in
commit
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