[PATCH net v2 09/10] 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.

Fixes: 4b623f9f0f59 ("net-shapers: implement NL get operation")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/shaper/shaper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/shaper/shaper.c b/net/shaper/shaper.c
index eb049847fed6..4ae3ee6764a0 100644
--- a/net/shaper/shaper.c
+++ b/net/shaper/shaper.c
@@ -482,6 +482,12 @@ static int net_shaper_parse_handle(const struct nlattr *attr,
 	else if (handle->scope == NET_SHAPER_SCOPE_NODE)
 		id = NET_SHAPER_ID_UNSPEC;
 
+	if (id && handle->scope == NET_SHAPER_SCOPE_NETDEV) {
+		NL_SET_ERR_MSG_ATTR(info->extack, id_attr,
+				    "Netdev scope is a singleton, must use ID 0");
+		return -EINVAL;
+	}
+
 	handle->id = id;
 	return 0;
 }
-- 
2.54.0