[PATCH net-next v1] net: devmem: document that bind-tx is unprivileged by design

[Mina Almasry <almasrymina@google.com>]

Unlike bind-rx, which configures shared NIC RX queues to steer incoming
traffic into the caller's dmabuf and requires CAP_NET_ADMIN
(uns-admin-perm), bind-tx only DMA-maps the caller's dmabuf so the caller
can transmit from it on their own sockets without affecting other traffic
or device configuration.

Add a comment in netdev.yaml and above netdev_nl_bind_tx_doit() to make it
explicit that NETDEV_CMD_BIND_TX is unprivileged by design.

Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 Documentation/netlink/specs/netdev.yaml | 2 ++
 net/core/netdev-genl.c                  | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index e13461cf3fc33..4303593e5003c 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml
@@ -852,6 +852,8 @@ operations:
       name: bind-tx
       doc: Bind dmabuf to netdev for TX
       attribute-set: dmabuf
+      # Intentionally unprivileged (no admin-perm / uns-admin-perm); see
+      # comment above netdev_nl_bind_tx_doit().
       do:
         request:
           attributes:
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index fa9edfdb32c29..690c27f63d260 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -1180,6 +1180,12 @@ netdev_find_netmem_tx_dev(struct net_device *dev)
 	return NULL;
 }
 
+/* Note: NETDEV_CMD_BIND_TX is intentionally unprivileged (no
+ * GENL_ADMIN_PERM / GENL_UNS_ADMIN_PERM). Unlike bind-rx, which configures
+ * shared NIC RX queues, bind-tx only DMA-maps the caller's dmabuf so they can
+ * transmit from it on their own sockets without affecting other traffic or
+ * device state.
+ */
 int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
 {
 	struct net_devmem_dmabuf_binding *binding;

base-commit: 8830e65ed46de41f849eefb8ba227d4852c460f6
-- 
2.55.0.1082.g2b9226bbc0-goog