[PATCH net v3] net: qualcomm: rmnet: require CAP_NET_ADMIN in the real device netns for config ops

["user.email" <suruurism@gmail.com>]

From: Abdifatah Suruur <suruurism@gmail.com>

An rmnet device may be created with its real device in a different
netns than the rmnet device itself (rmnet_newlink() resolves it in
link_net), and the rtnl config paths below only check CAP_NET_ADMIN
against dev_net(dev), while mutating rmnet port state attached to the
real device:

- rmnet_changelink() rewrites the endpoint mux table and
  port->data_format and, via rmnet_vnd_update_dev_mtu(), can shrink the
  MTU of the rmnet endpoint netdevs.
- rmnet_add_bridge() and rmnet_del_bridge(), reachable via
  ndo_add_slave/ndo_del_slave through RTM_SETLINK IFLA_MASTER, flip
  port->rmnet_mode and port->bridge_ep on the real device's port; with
  bridge_ep pointing at a caller-owned device, rmnet_rx_handler() then
  forwards real-device ingress frames to it.

A caller privileged only in the rmnet device's netns can therefore
rewrite the shared cellular data-path state owned by another netns, and
steer its ingress traffic.

Gate all three with rtnl_dev_link_net_capable(), matching the "require
CAP_NET_ADMIN in the device netns for changelink" series (vxlan/geneve,
CVE-2026-68432).

Fixes: 2abb5792387e ("net: qualcomm: rmnet: Allow configuration updates to existing devices")
Fixes: 60d58f971c1077 ("net: qualcomm: rmnet: Implement bridge mode")
Cc: stable@vger.kernel.org
Signed-off-by: Abdifatah Suruur <suruurism@gmail.com>
---
v3:
- cover rmnet_add_bridge() and rmnet_del_bridge() with the same gate;
  they mutate the same real-device port state via ndo_add_slave/
  ndo_del_slave and have no capability check of their own
- correct the impact wording: rmnet_vnd_update_dev_mtu() only reads
  real_dev->mtu; the MTU store lands on the rmnet endpoint netdevs via
  rmnet_vnd_change_mtu(), not on the real device
v2:
- drop Reported-by: (implied for the author), per Jakub Kicinski
---
 .../ethernet/qualcomm/rmnet/rmnet_config.c    | 30 ++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
index 78d4df55740a1..50c60e553d09f 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
@@ -312,6 +312,14 @@ static int rmnet_changelink(struct net_device *dev, struct nlattr *tb[],
 	if (!rmnet_is_real_dev_registered(real_dev))
 		return -ENODEV;
 
+	/*
+	 * The rtnl path only checks CAP_NET_ADMIN against dev_net(dev),
+	 * but the port state mutated below is attached to real_dev, which
+	 * may live in a different netns.
+	 */
+	if (!rtnl_dev_link_net_capable(dev, dev_net(real_dev)))
+		return -EPERM;
+
 	port = rmnet_get_port_rtnl(real_dev);
 
 	if (data[IFLA_RMNET_MUX_ID]) {
@@ -440,6 +448,14 @@ int rmnet_add_bridge(struct net_device *rmnet_dev,
 	struct rmnet_port *port, *slave_port;
 	int err;
 
+	/*
+	 * The rtnl path only checks CAP_NET_ADMIN against dev_net(dev),
+	 * but the port state mutated below is attached to real_dev, which
+	 * may live in a different netns.
+	 */
+	if (!rtnl_dev_link_net_capable(rmnet_dev, dev_net(real_dev)))
+		return -EPERM;
+
 	port = rmnet_get_port_rtnl(real_dev);
 
 	/* If there is more than one rmnet dev attached, its probably being
@@ -488,7 +504,19 @@ int rmnet_add_bridge(struct net_device *rmnet_dev,
 int rmnet_del_bridge(struct net_device *rmnet_dev,
 		     struct net_device *slave_dev)
 {
-	struct rmnet_port *port = rmnet_get_port_rtnl(slave_dev);
+	struct rmnet_priv *priv = netdev_priv(rmnet_dev);
+	struct net_device *real_dev = priv->real_dev;
+	struct rmnet_port *port;
+
+	/*
+	 * The rtnl path only checks CAP_NET_ADMIN against dev_net(dev),
+	 * but rmnet_unregister_bridge() below clears the bridge state of
+	 * the real device's port, which may live in a different netns.
+	 */
+	if (!rtnl_dev_link_net_capable(rmnet_dev, dev_net(real_dev)))
+		return -EPERM;
+
+	port = rmnet_get_port_rtnl(slave_dev);
 
 	rmnet_unregister_bridge(port);
 
-- 
2.53.0