[PATCH net 0/2] neighbour: fix update of proxy neighbour

[PATCH net 0/2] neighbour: fix update of proxy neighbour

[Sabrina Dubroca]

While re-reading some "old" patches I ran into a small change of
behavior in commit dc2a27e524ac ("neighbour: Update pneigh_entry in
pneigh_create().").

The old behavior was not consistent between ->protocol and ->flags,
and didn't offer a way to clear protocol, so maybe it's better to
change that (7-years-old [1]) behavior. But then we should change
non-proxy neighbours as well to keep neigh/pneigh consistent.

[1] df9b0e30d44c ("neighbor: Add protocol attribute")

Sabrina Dubroca (2):
  neighbour: restore protocol != 0 check in pneigh update
  selftests: rtnetlink: add neighbour update test

 net/core/neighbour.c                     |  3 +-
 tools/testing/selftests/net/rtnetlink.sh | 55 ++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

-- 
2.51.2

[PATCH net 1/2] neighbour: restore protocol != 0 check in pneigh update

[Sabrina Dubroca]

Prior to commit dc2a27e524ac ("neighbour: Update pneigh_entry in
pneigh_create()."), a pneigh's protocol was updated only when the
value of the NDA_PROTOCOL attribute was non-0. While moving the code,
that check was removed. This is a small change of user-visible
behavior, and inconsistent with the (non-proxy) neighbour behavior.

Fixes: dc2a27e524ac ("neighbour: Update pneigh_entry in pneigh_create().")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 net/core/neighbour.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index a95cfe77f7f0..c56a4e7bf790 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -820,7 +820,8 @@ int pneigh_create(struct neigh_table *tbl, struct net *net,
 update:
 	WRITE_ONCE(n->flags, flags);
 	n->permanent = permanent;
-	WRITE_ONCE(n->protocol, protocol);
+	if (protocol)
+		WRITE_ONCE(n->protocol, protocol);
 out:
 	mutex_unlock(&tbl->phash_lock);
 	return err;
-- 
2.51.2

[PATCH net 2/2] selftests: rtnetlink: add neighbour update test

[Sabrina Dubroca]

Check that protocol and flags are updated correctly for
neighbour and pneigh entries.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 tools/testing/selftests/net/rtnetlink.sh | 55 ++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/tools/testing/selftests/net/rtnetlink.sh b/tools/testing/selftests/net/rtnetlink.sh
index 248c2b91fe42..5a5ff88321d5 100755
--- a/tools/testing/selftests/net/rtnetlink.sh
+++ b/tools/testing/selftests/net/rtnetlink.sh
@@ -28,6 +28,7 @@ ALL_TESTS="
 	kci_test_fdb_get
 	kci_test_fdb_del
 	kci_test_neigh_get
+	kci_test_neigh_update
 	kci_test_bridge_parent_id
 	kci_test_address_proto
 	kci_test_enslave_bonding
@@ -1160,6 +1161,60 @@ kci_test_neigh_get()
 	end_test "PASS: neigh get"
 }
 
+kci_test_neigh_update()
+{
+	dstip=10.0.2.4
+	dstmac=de:ad:be:ef:13:37
+	local ret=0
+
+	for proxy in "" "proxy" ; do
+		# add a neighbour entry without any flags
+		run_cmd ip neigh add $proxy $dstip dev "$devdummy" lladdr $dstmac nud permanent
+		run_cmd_grep $dstip ip neigh show $proxy
+		run_cmd_grep_fail "$dstip dev $devdummy .*\(managed\|use\|router\|extern\)" ip neigh show $proxy
+
+		# set the extern_learn flag, but no other
+		run_cmd ip neigh change $proxy $dstip dev "$devdummy" extern_learn
+		run_cmd_grep "$dstip dev $devdummy .* extern_learn" ip neigh show $proxy
+		run_cmd_grep_fail "$dstip dev $devdummy .* \(managed\|use\|router\)" ip neigh show $proxy
+
+		# flags are reset when not provided
+		run_cmd ip neigh change $proxy $dstip dev "$devdummy"
+		run_cmd_grep $dstip ip neigh show $proxy
+		run_cmd_grep_fail "$dstip dev $devdummy .* extern_learn" ip neigh show $proxy
+
+		# add a protocol
+		run_cmd ip neigh change $proxy $dstip dev "$devdummy" protocol boot
+		run_cmd_grep "$dstip dev $devdummy .* proto boot" ip neigh show $proxy
+
+		# protocol is retained when not provided
+		run_cmd ip neigh change $proxy $dstip dev "$devdummy"
+		run_cmd_grep "$dstip dev $devdummy .* proto boot" ip neigh show $proxy
+
+		# change protocol
+		run_cmd ip neigh change $proxy $dstip dev "$devdummy" protocol static
+		run_cmd_grep "$dstip dev $devdummy .* proto static" ip neigh show $proxy
+
+		# also check an extended flag for non-proxy neighs
+		if [ "$proxy" = "" ]; then
+			run_cmd ip neigh change $proxy $dstip dev "$devdummy" managed
+			run_cmd_grep "$dstip dev $devdummy managed" ip neigh show $proxy
+
+			run_cmd ip neigh change $proxy $dstip dev "$devdummy" lladdr $dstmac
+			run_cmd_grep_fail "$dstip dev $devdummy managed" ip neigh show $proxy
+		fi
+
+		run_cmd ip neigh del $proxy $dstip dev "$devdummy"
+	done
+
+	if [ $ret -ne 0 ];then
+		end_test "FAIL: neigh update"
+		return 1
+	fi
+
+	end_test "PASS: neigh update"
+}
+
 kci_test_bridge_parent_id()
 {
 	local ret=0
-- 
2.51.2

Re: [PATCH net 1/2] neighbour: restore protocol != 0 check in pneigh update

[David Ahern]

On 3/10/26 3:59 PM, Sabrina Dubroca wrote:
> Prior to commit dc2a27e524ac ("neighbour: Update pneigh_entry in
> pneigh_create()."), a pneigh's protocol was updated only when the
> value of the NDA_PROTOCOL attribute was non-0. While moving the code,
> that check was removed. This is a small change of user-visible
> behavior, and inconsistent with the (non-proxy) neighbour behavior.
> 
> Fixes: dc2a27e524ac ("neighbour: Update pneigh_entry in pneigh_create().")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> ---
>  net/core/neighbour.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

good find. Thanks, Sabrina

Reviewed-by: David Ahern <dsahern@kernel.org>

Re: [PATCH net 1/2] neighbour: restore protocol != 0 check in pneigh update

[Kuniyuki Iwashima]

On Tue, Mar 10, 2026 at 2:59 PM Sabrina Dubroca <sd@queasysnail.net> wrote:
>
> Prior to commit dc2a27e524ac ("neighbour: Update pneigh_entry in
> pneigh_create()."), a pneigh's protocol was updated only when the
> value of the NDA_PROTOCOL attribute was non-0. While moving the code,
> that check was removed. This is a small change of user-visible
> behavior, and inconsistent with the (non-proxy) neighbour behavior.
>
> Fixes: dc2a27e524ac ("neighbour: Update pneigh_entry in pneigh_create().")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>

Thanks for catching this !

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

Re: [PATCH net 2/2] selftests: rtnetlink: add neighbour update test

[Kuniyuki Iwashima]

On Tue, Mar 10, 2026 at 2:59 PM Sabrina Dubroca <sd@queasysnail.net> wrote:
>
> Check that protocol and flags are updated correctly for
> neighbour and pneigh entries.
>
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

Re: [PATCH net 0/2] neighbour: fix update of proxy neighbour

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 10 Mar 2026 22:59:15 +0100 you wrote:
> While re-reading some "old" patches I ran into a small change of
> behavior in commit dc2a27e524ac ("neighbour: Update pneigh_entry in
> pneigh_create().").
> 
> The old behavior was not consistent between ->protocol and ->flags,
> and didn't offer a way to clear protocol, so maybe it's better to
> change that (7-years-old [1]) behavior. But then we should change
> non-proxy neighbours as well to keep neigh/pneigh consistent.
> 
> [...]

Here is the summary with links:
  - [net,1/2] neighbour: restore protocol != 0 check in pneigh update
    https://git.kernel.org/netdev/net/c/cbada1048847
  - [net,2/2] selftests: rtnetlink: add neighbour update test
    https://git.kernel.org/netdev/net/c/68e76fc12df0

You are awesome, thank you!
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