[PATCH net v3] macsec: initialize SecY before registering the netdevice

[Haseeb Malik via B4 Relay <devnull+haseebulhaq55.gmail.com@kernel.org>]

From: Haseeb Malik <haseebulhaq55@gmail.com>

Creating a MACsec device with MAC offload over an LRO-capable lower
device triggers a warning in rtmsg_ifinfo_build_skb() when IPv4
forwarding is enabled by default.

register_netdevice() invokes inetdev_init(), which disables LRO and emits
a NETDEV_FEAT_CHANGE notification. This reaches macsec_fill_info() before
macsec_add_dev() initializes the SecY. key_len is still zero, so
macsec_fill_info() returns -EMSGSIZE and trips the WARN_ON in
rtmsg_ifinfo_build_skb(), even though the skb has enough space.

Even without the warning, notifications during registration can report
uninitialized SecY attributes, including the SCI. This ordering has existed
since the driver was introduced.

Initialize the SecY and apply the new-link attributes before registration.
Move MAC address inheritance into macsec_newlink() so the SCI can also be
initialized before registration-time notifications report it. Move the
per-CPU statistics and metadata destination allocation into ndo_init(),
and release partial allocations on failure.

Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Reported-by: syzbot+f2f6312ad1b5a0bfe316@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f2f6312ad1b5a0bfe316
Suggested-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lists.openwall.net/linux-kernel/2026/08/19/552
Signed-off-by: Haseeb Malik <haseebulhaq55@gmail.com>
---
Changes in v3:
- Correct the Fixes tag to the original MACsec driver commit, as pointed
  out by Sabrina. Explain that the initialization order predates the
  warning. No code changes from v2.
- Link to v2: https://lore.kernel.org/netdev/20260918-fix-macsec-net-v2-1-784203ec4836@gmail.com/

Changes in v2:
- Initialize the SCI before registration, including MAC address inheritance,
  so registration-time notifications carry the configured SCI.
- Wrap the per-CPU statistics allocation at 80 columns.
- Link to v1: https://lore.kernel.org/netdev/20260911-fix-macsec-net-v1-1-c82aa58ae741@gmail.com/
---
 drivers/net/macsec.c | 84 +++++++++++++++++++++++++++-------------------------
 1 file changed, 43 insertions(+), 41 deletions(-)

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 6f9f3aceffaa..78a19b134632 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3539,6 +3539,22 @@ static int macsec_dev_init(struct net_device *dev)
 	if (err)
 		return err;
 
+	err = -ENOMEM;
+	macsec->stats = netdev_alloc_pcpu_stats(struct pcpu_secy_stats);
+	if (!macsec->stats)
+		goto destroy_gro_cells;
+
+	macsec->secy.tx_sc.stats =
+		netdev_alloc_pcpu_stats(struct pcpu_tx_sc_stats);
+	if (!macsec->secy.tx_sc.stats)
+		goto free_secy_stats;
+
+	macsec->secy.tx_sc.md_dst = metadata_dst_alloc(0, METADATA_MACSEC,
+						       GFP_KERNEL);
+	if (!macsec->secy.tx_sc.md_dst)
+		goto free_tx_sc_stats;
+	macsec->secy.tx_sc.md_dst->u.macsec_info.sci = macsec->secy.sci;
+
 	macsec_inherit_tso_max(dev);
 
 	dev->hw_features = real_dev->hw_features & MACSEC_OFFLOAD_FEATURES;
@@ -3551,8 +3567,6 @@ static int macsec_dev_init(struct net_device *dev)
 
 	macsec_set_head_tail_room(dev);
 
-	if (is_zero_ether_addr(dev->dev_addr))
-		eth_hw_addr_inherit(dev, real_dev);
 	if (is_zero_ether_addr(dev->broadcast))
 		memcpy(dev->broadcast, real_dev->broadcast, dev->addr_len);
 
@@ -3560,6 +3574,14 @@ static int macsec_dev_init(struct net_device *dev)
 	netdev_hold(real_dev, &macsec->dev_tracker, GFP_KERNEL);
 
 	return 0;
+
+free_tx_sc_stats:
+	free_percpu(macsec->secy.tx_sc.stats);
+free_secy_stats:
+	free_percpu(macsec->stats);
+destroy_gro_cells:
+	gro_cells_destroy(&macsec->gro_cells);
+	return err;
 }
 
 static void macsec_dev_uninit(struct net_device *dev)
@@ -4116,26 +4138,11 @@ static sci_t dev_to_sci(struct net_device *dev, __be16 port)
 	return make_sci(dev->dev_addr, port);
 }
 
-static int macsec_add_dev(struct net_device *dev, sci_t sci, u8 icv_len)
+static void macsec_init_secy(struct net_device *dev, sci_t sci, u8 icv_len)
 {
 	struct macsec_dev *macsec = macsec_priv(dev);
 	struct macsec_secy *secy = &macsec->secy;
 
-	macsec->stats = netdev_alloc_pcpu_stats(struct pcpu_secy_stats);
-	if (!macsec->stats)
-		return -ENOMEM;
-
-	secy->tx_sc.stats = netdev_alloc_pcpu_stats(struct pcpu_tx_sc_stats);
-	if (!secy->tx_sc.stats)
-		return -ENOMEM;
-
-	secy->tx_sc.md_dst = metadata_dst_alloc(0, METADATA_MACSEC, GFP_KERNEL);
-	if (!secy->tx_sc.md_dst)
-		/* macsec and secy percpu stats will be freed when unregistering
-		 * net_device in macsec_free_netdev()
-		 */
-		return -ENOMEM;
-
 	if (sci == MACSEC_UNDEF_SCI)
 		sci = dev_to_sci(dev, MACSEC_PORT_ES);
 
@@ -4149,15 +4156,12 @@ static int macsec_add_dev(struct net_device *dev, sci_t sci, u8 icv_len)
 	secy->xpn = DEFAULT_XPN;
 
 	secy->sci = sci;
-	secy->tx_sc.md_dst->u.macsec_info.sci = sci;
 	secy->tx_sc.active = true;
 	secy->tx_sc.encoding_sa = DEFAULT_ENCODING_SA;
 	secy->tx_sc.encrypt = DEFAULT_ENCRYPT;
 	secy->tx_sc.send_sci = DEFAULT_SEND_SCI;
 	secy->tx_sc.end_station = false;
 	secy->tx_sc.scb = false;
-
-	return 0;
 }
 
 static struct lock_class_key macsec_netdev_addr_lock_key;
@@ -4220,6 +4224,24 @@ static int macsec_newlink(struct net_device *dev,
 	if (rx_handler && rx_handler != macsec_handle_frame)
 		return -EBUSY;
 
+	if (is_zero_ether_addr(dev->dev_addr))
+		eth_hw_addr_inherit(dev, real_dev);
+
+	if (data && data[IFLA_MACSEC_SCI])
+		sci = nla_get_sci(data[IFLA_MACSEC_SCI]);
+	else if (data && data[IFLA_MACSEC_PORT])
+		sci = dev_to_sci(dev, nla_get_be16(data[IFLA_MACSEC_PORT]));
+	else
+		sci = dev_to_sci(dev, MACSEC_PORT_ES);
+
+	/* Registration can notify listeners before returning. */
+	macsec_init_secy(dev, sci, icv_len);
+	if (data) {
+		err = macsec_changelink_common(dev, data);
+		if (err)
+			return err;
+	}
+
 	err = register_netdevice(dev);
 	if (err < 0)
 		return err;
@@ -4232,31 +4254,11 @@ static int macsec_newlink(struct net_device *dev,
 	if (err < 0)
 		goto unregister;
 
-	/* need to be already registered so that ->init has run and
-	 * the MAC addr is set
-	 */
-	if (data && data[IFLA_MACSEC_SCI])
-		sci = nla_get_sci(data[IFLA_MACSEC_SCI]);
-	else if (data && data[IFLA_MACSEC_PORT])
-		sci = dev_to_sci(dev, nla_get_be16(data[IFLA_MACSEC_PORT]));
-	else
-		sci = dev_to_sci(dev, MACSEC_PORT_ES);
-
 	if (rx_handler && sci_exists(real_dev, sci)) {
 		err = -EBUSY;
 		goto unlink;
 	}
 
-	err = macsec_add_dev(dev, sci, icv_len);
-	if (err)
-		goto unlink;
-
-	if (data) {
-		err = macsec_changelink_common(dev, data);
-		if (err)
-			goto del_dev;
-	}
-
 	/* If h/w offloading is available, propagate to the device */
 	if (macsec_is_offloaded(macsec)) {
 		const struct macsec_ops *ops;

---
base-commit: 78445023439506ebd83b86d40b1e428a3b309d4a
change-id: 20260911-fix-macsec-net-ff3bc5e7ab0a

Best regards,
-- 
Haseeb Malik <haseebulhaq55@gmail.com>