[PATCH net 0/2] nexthop: Do not flush blackhole nexthops when loopback goes down

[PATCH net 0/2] nexthop: Do not flush blackhole nexthops when loopback goes down

[Ido Schimmel]

From: Ido Schimmel <idosch@nvidia.com>

Patch #1 prevents blackhole nexthops from being flushed when the
loopback device goes down given that as far as user space is concerned,
these nexthops do not have a nexthop device.

Patch #2 adds a test case.

There are no regressions in fib_nexthops.sh with this change:

 # ./fib_nexthops.sh
 ...
 Tests passed: 165
 Tests failed:   0

Ido Schimmel (2):
  nexthop: Do not flush blackhole nexthops when loopback goes down
  selftests: fib_nexthops: Test blackhole nexthops when loopback goes
    down

 net/ipv4/nexthop.c                          | 10 +++++++---
 tools/testing/selftests/net/fib_nexthops.sh |  8 ++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

-- 
2.29.2

[PATCH net 1/2] nexthop: Do not flush blackhole nexthops when loopback goes down

[Ido Schimmel]

From: Ido Schimmel <idosch@nvidia.com>

As far as user space is concerned, blackhole nexthops do not have a
nexthop device and therefore should not be affected by the
administrative or carrier state of any netdev.

However, when the loopback netdev goes down all the blackhole nexthops
are flushed. This happens because internally the kernel associates
blackhole nexthops with the loopback netdev.

This behavior is both confusing to those not familiar with kernel
internals and also diverges from the legacy API where blackhole IPv4
routes are not flushed when the loopback netdev goes down:

 # ip route add blackhole 198.51.100.0/24
 # ip link set dev lo down
 # ip route show 198.51.100.0/24
 blackhole 198.51.100.0/24

Blackhole IPv6 routes are flushed, but at least user space knows that
they are associated with the loopback netdev:

 # ip -6 route show 2001:db8:1::/64
 blackhole 2001:db8:1::/64 dev lo metric 1024 pref medium

Fix this by only flushing blackhole nexthops when the loopback netdev is
unregistered.

Fixes: ab84be7e54fc ("net: Initial nexthop code")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reported-by: Donald Sharp <sharpd@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
---
 net/ipv4/nexthop.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
index f1c6cbdb9e43..743777bce179 100644
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -1399,7 +1399,7 @@ static int insert_nexthop(struct net *net, struct nexthop *new_nh,
 
 /* rtnl */
 /* remove all nexthops tied to a device being deleted */
-static void nexthop_flush_dev(struct net_device *dev)
+static void nexthop_flush_dev(struct net_device *dev, unsigned long event)
 {
 	unsigned int hash = nh_dev_hashfn(dev->ifindex);
 	struct net *net = dev_net(dev);
@@ -1411,6 +1411,10 @@ static void nexthop_flush_dev(struct net_device *dev)
 		if (nhi->fib_nhc.nhc_dev != dev)
 			continue;
 
+		if (nhi->reject_nh &&
+		    (event == NETDEV_DOWN || event == NETDEV_CHANGE))
+			continue;
+
 		remove_nexthop(net, nhi->nh_parent, NULL);
 	}
 }
@@ -2189,11 +2193,11 @@ static int nh_netdev_event(struct notifier_block *this,
 	switch (event) {
 	case NETDEV_DOWN:
 	case NETDEV_UNREGISTER:
-		nexthop_flush_dev(dev);
+		nexthop_flush_dev(dev, event);
 		break;
 	case NETDEV_CHANGE:
 		if (!(dev_get_flags(dev) & (IFF_RUNNING | IFF_LOWER_UP)))
-			nexthop_flush_dev(dev);
+			nexthop_flush_dev(dev, event);
 		break;
 	case NETDEV_CHANGEMTU:
 		info_ext = ptr;
-- 
2.29.2

[PATCH net 2/2] selftests: fib_nexthops: Test blackhole nexthops when loopback goes down

[Ido Schimmel]

From: Ido Schimmel <idosch@nvidia.com>

Test that blackhole nexthops are not flushed when the loopback device
goes down.

Output without previous patch:

 # ./fib_nexthops.sh -t basic

 Basic functional tests
 ----------------------
 TEST: List with nothing defined                                     [ OK ]
 TEST: Nexthop get on non-existent id                                [ OK ]
 TEST: Nexthop with no device or gateway                             [ OK ]
 TEST: Nexthop with down device                                      [ OK ]
 TEST: Nexthop with device that is linkdown                          [ OK ]
 TEST: Nexthop with device only                                      [ OK ]
 TEST: Nexthop with duplicate id                                     [ OK ]
 TEST: Blackhole nexthop                                             [ OK ]
 TEST: Blackhole nexthop with other attributes                       [ OK ]
 TEST: Blackhole nexthop with loopback device down                   [FAIL]
 TEST: Create group                                                  [ OK ]
 TEST: Create group with blackhole nexthop                           [FAIL]
 TEST: Create multipath group where 1 path is a blackhole            [ OK ]
 TEST: Multipath group can not have a member replaced by blackhole   [ OK ]
 TEST: Create group with non-existent nexthop                        [ OK ]
 TEST: Create group with same nexthop multiple times                 [ OK ]
 TEST: Replace nexthop with nexthop group                            [ OK ]
 TEST: Replace nexthop group with nexthop                            [ OK ]
 TEST: Nexthop group and device                                      [ OK ]
 TEST: Test proto flush                                              [ OK ]
 TEST: Nexthop group and blackhole                                   [ OK ]

 Tests passed:  19
 Tests failed:   2

Output with previous patch:

 # ./fib_nexthops.sh -t basic

 Basic functional tests
 ----------------------
 TEST: List with nothing defined                                     [ OK ]
 TEST: Nexthop get on non-existent id                                [ OK ]
 TEST: Nexthop with no device or gateway                             [ OK ]
 TEST: Nexthop with down device                                      [ OK ]
 TEST: Nexthop with device that is linkdown                          [ OK ]
 TEST: Nexthop with device only                                      [ OK ]
 TEST: Nexthop with duplicate id                                     [ OK ]
 TEST: Blackhole nexthop                                             [ OK ]
 TEST: Blackhole nexthop with other attributes                       [ OK ]
 TEST: Blackhole nexthop with loopback device down                   [ OK ]
 TEST: Create group                                                  [ OK ]
 TEST: Create group with blackhole nexthop                           [ OK ]
 TEST: Create multipath group where 1 path is a blackhole            [ OK ]
 TEST: Multipath group can not have a member replaced by blackhole   [ OK ]
 TEST: Create group with non-existent nexthop                        [ OK ]
 TEST: Create group with same nexthop multiple times                 [ OK ]
 TEST: Replace nexthop with nexthop group                            [ OK ]
 TEST: Replace nexthop group with nexthop                            [ OK ]
 TEST: Nexthop group and device                                      [ OK ]
 TEST: Test proto flush                                              [ OK ]
 TEST: Nexthop group and blackhole                                   [ OK ]

 Tests passed:  21
 Tests failed:   0

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
---
 tools/testing/selftests/net/fib_nexthops.sh | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/net/fib_nexthops.sh b/tools/testing/selftests/net/fib_nexthops.sh
index 4c7d33618437..d98fb85e201c 100755
--- a/tools/testing/selftests/net/fib_nexthops.sh
+++ b/tools/testing/selftests/net/fib_nexthops.sh
@@ -1524,6 +1524,14 @@ basic()
 	run_cmd "$IP nexthop replace id 2 blackhole dev veth1"
 	log_test $? 2 "Blackhole nexthop with other attributes"
 
+	# blackhole nexthop should not be affected by the state of the loopback
+	# device
+	run_cmd "$IP link set dev lo down"
+	check_nexthop "id 2" "id 2 blackhole"
+	log_test $? 0 "Blackhole nexthop with loopback device down"
+
+	run_cmd "$IP link set dev lo up"
+
 	#
 	# groups
 	#
-- 
2.29.2

Re: [PATCH net 0/2] nexthop: Do not flush blackhole nexthops when loopback goes down

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (refs/heads/master):

On Thu,  4 Mar 2021 10:57:52 +0200 you wrote:
> From: Ido Schimmel <idosch@nvidia.com>
> 
> Patch #1 prevents blackhole nexthops from being flushed when the
> loopback device goes down given that as far as user space is concerned,
> these nexthops do not have a nexthop device.
> 
> Patch #2 adds a test case.
> 
> [...]

Here is the summary with links:
  - [net,1/2] nexthop: Do not flush blackhole nexthops when loopback goes down
    https://git.kernel.org/netdev/net/c/76c03bf8e262
  - [net,2/2] selftests: fib_nexthops: Test blackhole nexthops when loopback goes down
    https://git.kernel.org/netdev/net/c/3a1099d3147f

You are awesome, thank you!
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