netdev - [PATCH net-next] rtnetlink: Allow setting IFLA_PERM

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Message-Id: <20250213-virt-dev-permaddr-v1-1-9a616b3de44b@redhat.com>
Date: Thu, 13 Feb 2025 14:45:22 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, 
 Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH net-next] rtnetlink: Allow setting IFLA_PERM_ADDRESS at
 device creation time

Eric suggested[0] allowing user-settable values for dev->perm_addr at
device creation time, instead of mucking about with netdevsim to get a
virtual device with a permanent address set.

The original use case for this was easing testing for network management
daemons that use the permanent address to match against. However, having
the ability to set a permanent identifier for a virtual device at
creation time seems generally useful, so decided to go for this approach
instead.

[0] https://lore.kernel.org/r/CANn89iK8YpzNhJv4R+x80hcq794bh_ykS-O-2UHziBXixNhzyA@mail.gmail.com

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 net/core/rtnetlink.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index cb7fad8d1f95ff287810229c341de6a6d20a9c07..38dec2ae1a19f91daf9200744c7497088ecc037e 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2224,7 +2224,7 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
 	[IFLA_PROP_LIST]	= { .type = NLA_NESTED },
 	[IFLA_ALT_IFNAME]	= { .type = NLA_STRING,
 				    .len = ALTIFNAMSIZ - 1 },
-	[IFLA_PERM_ADDRESS]	= { .type = NLA_REJECT },
+	[IFLA_PERM_ADDRESS]	= { .type = NLA_BINARY, .len = MAX_ADDR_LEN },
 	[IFLA_PROTO_DOWN_REASON] = { .type = NLA_NESTED },
 	[IFLA_NEW_IFINDEX]	= NLA_POLICY_MIN(NLA_S32, 1),
 	[IFLA_PARENT_DEV_NAME]	= { .type = NLA_NUL_STRING },
@@ -2647,7 +2647,7 @@ static	int rtnl_set_vf_rate(struct net_device *dev, int vf, int min_tx_rate,
 }
 
 static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
-			    struct netlink_ext_ack *extack)
+			    struct netlink_ext_ack *extack, bool create)
 {
 	if (tb[IFLA_ADDRESS] &&
 	    nla_len(tb[IFLA_ADDRESS]) < dev->addr_len)
@@ -2657,6 +2657,17 @@ static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
 	    nla_len(tb[IFLA_BROADCAST]) < dev->addr_len)
 		return -EINVAL;
 
+	if (tb[IFLA_PERM_ADDRESS]) {
+		if (!create) {
+			NL_SET_ERR_MSG(extack,
+				       "can't change permanent address");
+			return -EINVAL;
+		}
+
+		if (nla_len(tb[IFLA_PERM_ADDRESS]) < dev->addr_len)
+			return -EINVAL;
+	}
+
 	if (tb[IFLA_GSO_MAX_SIZE] &&
 	    nla_get_u32(tb[IFLA_GSO_MAX_SIZE]) > dev->tso_max_size) {
 		NL_SET_ERR_MSG(extack, "too big gso_max_size");
@@ -3010,7 +3021,7 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
 	char ifname[IFNAMSIZ];
 	int err;
 
-	err = validate_linkmsg(dev, tb, extack);
+	err = validate_linkmsg(dev, tb, extack, false);
 	if (err < 0)
 		goto errout;
 
@@ -3614,7 +3625,7 @@ struct net_device *rtnl_create_link(struct net *net, const char *ifname,
 	if (!dev)
 		return ERR_PTR(-ENOMEM);
 
-	err = validate_linkmsg(dev, tb, extack);
+	err = validate_linkmsg(dev, tb, extack, true);
 	if (err < 0) {
 		free_netdev(dev);
 		return ERR_PTR(err);
@@ -3642,6 +3653,9 @@ struct net_device *rtnl_create_link(struct net *net, const char *ifname,
 	if (tb[IFLA_BROADCAST])
 		memcpy(dev->broadcast, nla_data(tb[IFLA_BROADCAST]),
 				nla_len(tb[IFLA_BROADCAST]));
+	if (tb[IFLA_PERM_ADDRESS])
+		memcpy(dev->perm_addr, nla_data(tb[IFLA_PERM_ADDRESS]),
+		       nla_len(tb[IFLA_PERM_ADDRESS]));
 	if (tb[IFLA_TXQLEN])
 		dev->tx_queue_len = nla_get_u32(tb[IFLA_TXQLEN]);
 	if (tb[IFLA_OPERSTATE])

---
base-commit: 7aca0d8a727da503a8adeb6866a136ded5bea4b1
change-id: 20250213-virt-dev-permaddr-7d7dca7c6cb3