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

[subash.a.kasiviswanathan]

> -----Original Message-----
> From: user.email <suruurism@xxxxxxxxx>
> Sent: Saturday, August 29, 2026 11:07 AM
> To: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Cc: subash.a.kasiviswanathan@xxxxxxxxxxxxxxxx;
> sean.tranchetti@xxxxxxxxxxxxxxxx; horms@xxxxxxxxxx
> Subject: [PATCH net v3] net: qualcomm: rmnet: require CAP_NET_ADMIN in
> the real device netns for config ops
> 
> From: Abdifatah Suruur <suruurism@xxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Abdifatah Suruur <suruurism@xxxxxxxxx>
> ---
> 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

The change itself is fine though you might need to update the comment style
to match the networking convention
https://www.kernel.org/doc/html/v5.7/networking/netdev-FAQ.html#q-is-the-com
ment-style-convention-different-for-the-networking-content

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
index bed6f63facf2..5d0a4a428e97 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
@@ -312,6 +312,13 @@ 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]) {
@@ -441,6 +448,13 @@ 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
@@ -489,7 +503,18 @@ 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);