netdev - [PATCH net-next v2] ipv6: preserve insertion order for same-scope addresses

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Message-ID: <20260104032357.38555-1-yuhuang@redhat.com>
Date: Sun,  4 Jan 2026 11:23:57 +0800
From: Yumei Huang <yuhuang@...hat.com>
To: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Cc: sbrivio@...hat.com,
	david@...son.dropbear.id.au,
	yuhuang@...hat.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	justin.iurman@...ege.be,
	shuah@...nel.org
Subject: [PATCH net-next v2] ipv6: preserve insertion order for same-scope addresses

IPv6 addresses with the same scope are returned in reverse insertion
order, unlike IPv4. For example, when adding a -> b -> c, the list is
reported as c -> b -> a, while IPv4 preserves the original order.

This behavior causes:

a. When using `ip -6 a save` and `ip -6 a restore`, addresses are restored
   in the opposite order from which they were saved. See example below
   showing addresses added as 1::1, 1::2, 1::3 but displayed and saved
   in reverse order.

   # ip -6 a a 1::1 dev x
   # ip -6 a a 1::2 dev x
   # ip -6 a a 1::3 dev x
   # ip -6 a s dev x
   2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
       inet6 1::3/128 scope global tentative
       valid_lft forever preferred_lft forever
       inet6 1::2/128 scope global tentative
       valid_lft forever preferred_lft forever
       inet6 1::1/128 scope global tentative
       valid_lft forever preferred_lft forever
   # ip -6 a save > dump
   # ip -6 a d 1::1 dev x
   # ip -6 a d 1::2 dev x
   # ip -6 a d 1::3 dev x
   # ip a d ::1 dev lo
   # ip a restore < dump
   # ip -6 a s dev x
   2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
       inet6 1::1/128 scope global tentative
       valid_lft forever preferred_lft forever
       inet6 1::2/128 scope global tentative
       valid_lft forever preferred_lft forever
       inet6 1::3/128 scope global tentative
       valid_lft forever preferred_lft forever
   # ip a showdump < dump
    if1:
        inet6 ::1/128 scope host proto kernel_lo
        valid_lft forever preferred_lft forever
    if2:
        inet6 1::3/128 scope global tentative
        valid_lft forever preferred_lft forever
    if2:
        inet6 1::2/128 scope global tentative
        valid_lft forever preferred_lft forever
    if2:
        inet6 1::1/128 scope global tentative
        valid_lft forever preferred_lft forever

b. Addresses in pasta to appear in reversed order compared to host
   addresses.

The ipv6 addresses were added in reverse order by commit e55ffac60117
("[IPV6]: order addresses by scope"), then it was changed by commit
502a2ffd7376 ("ipv6: convert idev_list to list macros"), and restored by
commit b54c9b98bbfb ("ipv6: Preserve pervious behavior in
ipv6_link_dev_addr()."). However, this reverse ordering within the same
scope causes inconsistency with IPv4 and the issues described above.

This patch aligns IPv6 address ordering with IPv4 for consistency
by changing the comparison from >= to > when inserting addresses
into the address list. Also updates the ioam6 selftest to reflect
the new address ordering behavior. Combine these two changes into
one patch for bisectability.

Fixes: e55ffac60117 ("[IPV6]: order addresses by scope")
Link: https://bugs.passt.top/show_bug.cgi?id=175
Suggested-by: Stefano Brivio <sbrivio@...hat.com>
Signed-off-by: Yumei Huang <yuhuang@...hat.com>
---
 net/ipv6/addrconf.c                  | 2 +-
 tools/testing/selftests/net/ioam6.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 40e9c336f6c5..ca998bf46863 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1013,7 +1013,7 @@ ipv6_link_dev_addr(struct inet6_dev *idev, struct inet6_ifaddr *ifp)
 	list_for_each(p, &idev->addr_list) {
 		struct inet6_ifaddr *ifa
 			= list_entry(p, struct inet6_ifaddr, if_list);
-		if (ifp_scope >= ipv6_addr_src_scope(&ifa->addr))
+		if (ifp_scope > ipv6_addr_src_scope(&ifa->addr))
 			break;
 	}
 
diff --git a/tools/testing/selftests/net/ioam6.sh b/tools/testing/selftests/net/ioam6.sh
index 845c26dd01a9..b2b99889942f 100755
--- a/tools/testing/selftests/net/ioam6.sh
+++ b/tools/testing/selftests/net/ioam6.sh
@@ -273,8 +273,8 @@ setup()
   ip -netns $ioam_node_beta link set ioam-veth-betaR name veth1 &>/dev/null
   ip -netns $ioam_node_gamma link set ioam-veth-gamma name veth0 &>/dev/null
 
-  ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
   ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
+  ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
   ip -netns $ioam_node_alpha link set veth0 up &>/dev/null
   ip -netns $ioam_node_alpha link set lo up &>/dev/null
   ip -netns $ioam_node_alpha route add 2001:db8:2::/64 \
-- 
2.52.0