[PATCH 5.2 003/313] ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule

[Greg Kroah-Hartman]

From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>

[ Upstream commit ca7a03c4175366a92cee0ccc4fec0038c3266e26 ]

Commit 7d9e5f422150 removed references from certain dsts, but accounting
for this never translated down into the fib6 suppression code. This bug
was triggered by WireGuard users who use wg-quick(8), which uses the
"suppress-prefix" directive to ip-rule(8) for routing all of their
internet traffic without routing loops. The test case added here
causes the reference underflow by causing packets to evaluate a suppress
rule.

Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Acked-by: Wei Wang <weiwan@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv6/fib6_rules.c                    |    3 ++-
 tools/testing/selftests/net/fib_tests.sh |   17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

--- a/net/ipv6/fib6_rules.c
+++ b/net/ipv6/fib6_rules.c
@@ -285,7 +285,8 @@ static bool fib6_rule_suppress(struct fi
 	return false;
 
 suppress_route:
-	ip6_rt_put(rt);
+	if (!(arg->flags & FIB_LOOKUP_NOREF))
+		ip6_rt_put(rt);
 	return true;
 }
 
--- a/tools/testing/selftests/net/fib_tests.sh
+++ b/tools/testing/selftests/net/fib_tests.sh
@@ -9,7 +9,7 @@ ret=0
 ksft_skip=4
 
 # all tests in this script. Can be overridden with -t option
-TESTS="unregister down carrier nexthop ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw"
+TESTS="unregister down carrier nexthop suppress ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw"
 
 VERBOSE=0
 PAUSE_ON_FAIL=no
@@ -582,6 +582,20 @@ fib_nexthop_test()
 	cleanup
 }
 
+fib_suppress_test()
+{
+	$IP link add dummy1 type dummy
+	$IP link set dummy1 up
+	$IP -6 route add default dev dummy1
+	$IP -6 rule add table main suppress_prefixlength 0
+	ping -f -c 1000 -W 1 1234::1 || true
+	$IP -6 rule del table main suppress_prefixlength 0
+	$IP link del dummy1
+
+	# If we got here without crashing, we're good.
+	return 0
+}
+
 ################################################################################
 # Tests on route add and replace
 
@@ -1558,6 +1572,7 @@ do
 	fib_down_test|down)		fib_down_test;;
 	fib_carrier_test|carrier)	fib_carrier_test;;
 	fib_nexthop_test|nexthop)	fib_nexthop_test;;
+	fib_suppress_test|suppress)	fib_suppress_test;;
 	ipv6_route_test|ipv6_rt)	ipv6_route_test;;
 	ipv4_route_test|ipv4_rt)	ipv4_route_test;;
 	ipv6_addr_metric)		ipv6_addr_metric_test;;