netdev - [PATCH net-next 1/3] net: ipv4: Allow changing IPv4 address protocol

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Message-ID: <6ffecb0f77dc6e444e3a130a09b4fd5d717e6504.1679399108.git.petrm@nvidia.com>
Date:   Tue, 21 Mar 2023 12:51:59 +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>,
        Jacques de Laval <Jacques.De.Laval@...termo.com>,
        Petr Machata <petrm@...dia.com>
Subject: [PATCH net-next 1/3] net: ipv4: Allow changing IPv4 address protocol

When IP address protocol field was added in commit 47f0bd503210 ("net: Add
new protocol attribute to IP addresses"), the semantics included the
ability to change the protocol for IPv6 addresses, but not for IPv4
addresses. It seems this was not deliberate, but rather by accident.

A userspace that wants to change the protocol of an address might drop and
recreate the address, but that disrupts routing and is just impractical.

So in this patch, when an IPv4 address is replaced (through RTM_NEWADDR
request with NLM_F_REPLACE flag), update the proto at the address to the
one given in the request, or zero if none is given. This matches the
behavior of IPv6. Previously, any new value given was simply ignored.

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/ipv4/devinet.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index b0acf6e19aed..5deac0517ef7 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -962,6 +962,7 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 					 extack);
 	} else {
 		u32 new_metric = ifa->ifa_rt_priority;
+		u8 new_proto = ifa->ifa_proto;

 		inet_free_ifa(ifa);

@@ -975,6 +976,8 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			ifa->ifa_rt_priority = new_metric;
 		}

+		ifa->ifa_proto = new_proto;
+
 		set_ifa_lifetime(ifa, valid_lft, prefered_lft);
 		cancel_delayed_work(&check_lifetime_work);
 		queue_delayed_work(system_power_efficient_wq,
-- 
2.39.0