[PATCH 5.4 020/152] ipv6: Fix route replacement with dev-only route

Greg Kroah-Hartman
2020-03-03T17:52:53Z

From: Benjamin Poirier <bpoirier@cumulusnetworks.com>

[ Upstream commit e404b8c7cfb31654c9024d497cec58a501501692 ]

After commit 27596472473a ("ipv6: fix ECMP route replacement") it is no
longer possible to replace an ECMP-able route by a non ECMP-able route.
For example,
ip route add 2001:db8::1/128 via fe80::1 dev dummy0
ip route replace 2001:db8::1/128 dev dummy0
does not work as expected.

Tweak the replacement logic so that point 3 in the log of the above commit
becomes:
3. If the new route is not ECMP-able, and no matching non-ECMP-able route
exists, replace matching ECMP-able route (if any) or add the new route.

We can now summarize the entire replace semantics to:
When doing a replace, prefer replacing a matching route of the same
"ECMP-able-ness" as the replace argument. If there is no such candidate,
fallback to the first route found.

Fixes: 27596472473a ("ipv6: fix ECMP route replacement")
Signed-off-by: Benjamin Poirier <bpoirier@cumulusnetworks.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/ip6_fib.c | 7 ++++---
tools/testing/selftests/net/fib_tests.sh | 6 ++++++
2 files changed, 10 insertions(+), 3 deletions(-)

--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1050,8 +1050,7 @@ static int fib6_add_rt2node(struct fib6_
found++;
break;
}
- if (rt_can_ecmp)
- fallback_ins = fallback_ins ?: ins;
+ fallback_ins = fallback_ins ?: ins;
goto next_iter;
}

@@ -1094,7 +1093,9 @@ next_iter:
}

if (fallback_ins && !found) {
- /* No ECMP-able route found, replace first non-ECMP one */
+ /* No matching route with same ecmp-able-ness found, replace
+ * first matching route
+ */
ins = fallback_ins;
iter = rcu_dereference_protected(*ins,
lockdep_is_held(&rt->fib6_table->tb6_lock));
--- a/tools/testing/selftests/net/fib_tests.sh
+++ b/tools/testing/selftests/net/fib_tests.sh
@@ -910,6 +910,12 @@ ipv6_rt_replace_mpath()
check_route6 "2001:db8:104::/64 via 2001:db8:101::3 dev veth1 metric 1024"
log_test $? 0 "Multipath with single path via multipath attribute"

+ # multipath with dev-only
+ add_initial_route6 "nexthop via 2001:db8:101::2 nexthop via 2001:db8:103::2"
+ run_cmd "$IP -6 ro replace 2001:db8:104::/64 dev veth1"
+ check_route6 "2001:db8:104::/64 dev veth1 metric 1024"
+ log_test $? 0 "Multipath with dev-only"
+
# route replace fails - invalid nexthop 1
add_initial_route6 "nexthop via 2001:db8:101::2 nexthop via 2001:db8:103::2"
run_cmd "$IP -6 ro replace 2001:db8:104::/64 nexthop via 2001:db8:111::3 nexthop via 2001:db8:103::3"