[PATCH net 11/12] net: shaper: enforce singleton NETDEV scope with id 0

[Jakub Kicinski <kuba@kernel.org>]

The NETDEV scope represents a singleton root shaper in the per-device
hierarchy.  All code assumes NETDEV shapers have id 0:
net_shaper_default_parent() hardcodes parent->id = 0 when returning
the NETDEV parent for QUEUE/NODE children, and the UAPI documentation
describes NETDEV scope as "the main shaper" (singular, not plural).

Make sure we reject non-0 IDs like we reject out of range queues.

Fixes: 4b623f9f0f59 ("net-shapers: implement NL get operation")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/shaper/shaper.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/shaper/shaper.c b/net/shaper/shaper.c
index 16bf24d9e3ca..2adf8b0e1105 100644
--- a/net/shaper/shaper.c
+++ b/net/shaper/shaper.c
@@ -535,6 +535,13 @@ static int net_shaper_validate_caps(struct net_shaper_binding *binding,
 		return -EOPNOTSUPP;
 	}
 
+	if (shaper->handle.scope == NET_SHAPER_SCOPE_NETDEV &&
+	    shaper->handle.id != 0) {
+		NL_SET_ERR_MSG(info->extack,
+			       "Netdev scope is a singleton, must use ID 0");
+		return -EINVAL;
+	}
+
 	if (shaper->handle.scope == NET_SHAPER_SCOPE_QUEUE &&
 	    binding->type == NET_SHAPER_BINDING_TYPE_NETDEV &&
 	    shaper->handle.id >= binding->netdev->real_num_tx_queues) {
-- 
2.54.0