netdev - [PATCH net-next 1/5] net: ipv4: Allow changing IPv4 labels

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Date:   Fri, 10 Mar 2023 12:44:54 +0100
From:   Petr Machata <petrm@...dia.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, <netdev@...r.kernel.org>
CC:     David Ahern <dsahern@...nel.org>, Shuah Khan <shuah@...nel.org>,
        "Ido Schimmel" <idosch@...dia.com>,
        Petr Machata <petrm@...dia.com>, <mlxsw@...dia.com>
Subject: [PATCH net-next 1/5] net: ipv4: Allow changing IPv4 labels

IPv4 addresses can be tagged with label strings. Unlike IPv6 addrlabels,
which are used for prioritization of IPv6 addresses, these "ip address
labels" are simply tags that the userspace can assign to IP addresses
arbitrarily.

IPv4 has had support for these tags since before Linux was tracked in GIT.
However it has never been possible to change the label after it is once
defined. This limits usefulness of this feature. A userspace that wants to
change a label might drop and recreate the address, but that disrupts
routing and is just impractical.

In this patch, when an address is replaced (through RTM_NEWADDR request
with NLM_F_REPLACE flag) and a label (IFA_LABEL) is given, update the label
at the address to the one given in the request. So far the new value was
simply ignored.

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/ipv4/devinet.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index b0acf6e19aed..dfb6d20ada9a 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -823,6 +823,7 @@ static void set_ifa_lifetime(struct in_ifaddr *ifa, __u32 valid_lft,
 
 static struct in_ifaddr *rtm_to_ifaddr(struct net *net, struct nlmsghdr *nlh,
 				       __u32 *pvalid_lft, __u32 *pprefered_lft,
+				       const struct nlattr **at_label,
 				       struct netlink_ext_ack *extack)
 {
 	struct nlattr *tb[IFA_MAX+1];
@@ -885,6 +886,8 @@ static struct in_ifaddr *rtm_to_ifaddr(struct net *net, struct nlmsghdr *nlh,
 		nla_strscpy(ifa->ifa_label, tb[IFA_LABEL], IFNAMSIZ);
 	else
 		memcpy(ifa->ifa_label, dev->name, IFNAMSIZ);
+	if (at_label)
+		*at_label = tb[IFA_LABEL];
 
 	if (tb[IFA_RT_PRIORITY])
 		ifa->ifa_rt_priority = nla_get_u32(tb[IFA_RT_PRIORITY]);
@@ -933,6 +936,7 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			    struct netlink_ext_ack *extack)
 {
 	struct net *net = sock_net(skb->sk);
+	const struct nlattr *at_label;
 	struct in_ifaddr *ifa;
 	struct in_ifaddr *ifa_existing;
 	__u32 valid_lft = INFINITY_LIFE_TIME;
@@ -940,7 +944,8 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	ASSERT_RTNL();
 
-	ifa = rtm_to_ifaddr(net, nlh, &valid_lft, &prefered_lft, extack);
+	ifa = rtm_to_ifaddr(net, nlh, &valid_lft, &prefered_lft, &at_label,
+			    extack);
 	if (IS_ERR(ifa))
 		return PTR_ERR(ifa);
 
@@ -975,6 +980,9 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			ifa->ifa_rt_priority = new_metric;
 		}
 
+		if (at_label)
+			nla_strscpy(ifa->ifa_label, at_label, IFNAMSIZ);
+
 		set_ifa_lifetime(ifa, valid_lft, prefered_lft);
 		cancel_delayed_work(&check_lifetime_work);
 		queue_delayed_work(system_power_efficient_wq,
-- 
2.39.0