Re: [PATCH net] net: devmem: check uid and netns in net_devmem_get_binding()

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Mon, Oct 05, 2026 at 09:04:03PM +0000, Kaifeng Wang wrote:
> NETDEV_CMD_BIND_TX is unprivileged, and dmabuf binding IDs are allocated
> from a single global xarray. Currently net_devmem_get_binding() looks up
> the binding by ID without checking whether the sending socket belongs to
> the same user or network namespace that created the binding.
> 
> Record the creating netlink socket's network namespace and UID on the
> binding, and verify both in net_devmem_get_binding() before checking the
> route destination device. Return -EINVAL on mismatch so callers cannot
> distinguish non-existent IDs from bindings owned by other users.
> 
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Signed-off-by: Kaifeng Wang <kaifengw@google.com>
> ---
>  net/core/devmem.c      | 7 ++++++-
>  net/core/devmem.h      | 5 +++++
>  net/core/netdev-genl.c | 5 +++--
>  3 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index f4d60654ce7f..9a773b1ce92d 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -191,6 +191,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>  		       enum dma_data_direction direction,
>  		       unsigned int dmabuf_fd, unsigned int niov_shift,
>  		       struct netdev_nl_sock *priv,
> +		       const struct sock *nl_sk,
>  		       struct netlink_ext_ack *extack)
>  {
>  	struct net_devmem_dmabuf_binding *binding;
> @@ -220,6 +221,8 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>  
>  	binding->dev = dev;
>  	binding->vdev = vdev;
> +	write_pnet(&binding->net, sock_net(nl_sk));
> +	binding->uid = sk_uid(nl_sk);
>  	binding->niov_shift = niov_shift;
>  	xa_init_flags(&binding->bound_rxqs, XA_FLAGS_ALLOC);
>  
> @@ -390,7 +393,9 @@ struct net_devmem_dmabuf_binding *net_devmem_get_binding(struct sock *sk,
>  	int err = 0;
>  
>  	binding = net_devmem_lookup_dmabuf(dmabuf_id);
> -	if (!binding || !binding->tx_vec) {
> +	if (!binding || !binding->tx_vec ||
> +	    !net_eq(sock_net(sk), read_pnet(&binding->net)) ||
> +	    !uid_eq(sk_uid(sk), binding->uid)) {
>  		err = -EINVAL;
>  		goto out_err;
>  	}
> diff --git a/net/core/devmem.h b/net/core/devmem.h
> index 4a293a7d1149..7b9d3e04367c 100644
> --- a/net/core/devmem.h
> +++ b/net/core/devmem.h
> @@ -10,6 +10,7 @@
>  #ifndef _NET_DEVMEM_H
>  #define _NET_DEVMEM_H
>  
> +#include <net/net_namespace.h>
>  #include <net/netmem.h>
>  #include <net/netdev_netlink.h>
>  
> @@ -26,6 +27,8 @@ struct net_devmem_dmabuf_binding {
>  	 * dereferenced.
>  	 */
>  	void *vdev;
> +	possible_net_t net;
> +	kuid_t uid;
>  	struct gen_pool *chunk_pool;
>  	/* Protect dev */
>  	struct mutex lock;
> @@ -97,6 +100,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>  		       enum dma_data_direction direction,
>  		       unsigned int dmabuf_fd, unsigned int niov_shift,
>  		       struct netdev_nl_sock *priv,
> +		       const struct sock *nl_sk,
>  		       struct netlink_ext_ack *extack);
>  struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id);
>  void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding);
> @@ -181,6 +185,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>  		       unsigned int dmabuf_fd,
>  		       unsigned int niov_shift,
>  		       struct netdev_nl_sock *priv,
> +		       const struct sock *nl_sk,
>  		       struct netlink_ext_ack *extack)
>  {
>  	return ERR_PTR(-EOPNOTSUPP);
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index 33b9f4eb9565..847814e3df3f 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -1094,7 +1094,7 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>  
>  	binding = net_devmem_bind_dmabuf(netdev, NULL, dma_dev, DMA_FROM_DEVICE,
>  					 dmabuf_fd, niov_shift, priv,
> -					 info->extack);
> +					 NETLINK_CB(skb).sk, info->extack);
>  	if (IS_ERR(binding)) {
>  		err = PTR_ERR(binding);
>  		goto err_rxq_bitmap;
> @@ -1243,7 +1243,8 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>  	binding = net_devmem_bind_dmabuf(bind_dev,
>  					 bind_dev != netdev ? netdev : NULL,
>  					 dma_dev, DMA_TO_DEVICE, dmabuf_fd,
> -					 PAGE_SHIFT, priv, info->extack);
> +					 PAGE_SHIFT, priv, NETLINK_CB(skb).sk,
> +					 info->extack);
>  	if (IS_ERR(binding)) {
>  		err = PTR_ERR(binding);
>  		goto err_unlock_bind_dev;
> -- 
> 2.56.0.rc1.315.gc6ed9934b7-goog
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>