netdev: prevent accessing NAPI instances from another namespace

The NAPI IDs were not fully exposed to user space prior to the netlink
API, so they were never namespaced. The netlink API must ensure that
at the very least NAPI instance belongs to the same netns as the owner
of the genl sock.

napi_by_id() can become static now, but it needs to move because of
dev_get_by_napi_id().

Cc: stable@vger.kernel.org
Fixes: 1287c1ae0fc2 ("netdev-genl: Support setting per-NAPI config values")
Fixes: 27f91aaf49b3 ("netdev-genl: Add netlink framework functions for napi")
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250106180137.1861472-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 30 insertions, 13 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index faa23042df38..a9f62f5aeb84 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -753,6 +753,36 @@ int dev_fill_forward_path(const struct net_device *dev, const u8 *daddr,
 }
 EXPORT_SYMBOL_GPL(dev_fill_forward_path);
 
+/* must be called under rcu_read_lock(), as we dont take a reference */
+static struct napi_struct *napi_by_id(unsigned int napi_id)
+{
+	unsigned int hash = napi_id % HASH_SIZE(napi_hash);
+	struct napi_struct *napi;
+
+	hlist_for_each_entry_rcu(napi, &napi_hash[hash], napi_hash_node)
+		if (napi->napi_id == napi_id)
+			return napi;
+
+	return NULL;
+}
+
+/* must be called under rcu_read_lock(), as we dont take a reference */
+struct napi_struct *netdev_napi_by_id(struct net *net, unsigned int napi_id)
+{
+	struct napi_struct *napi;
+
+	napi = napi_by_id(napi_id);
+	if (!napi)
+		return NULL;
+
+	if (WARN_ON_ONCE(!napi->dev))
+		return NULL;
+	if (!net_eq(net, dev_net(napi->dev)))
+		return NULL;
+
+	return napi;
+}
+
 /**
  *	__dev_get_by_name	- find a device by its name
  *	@net: the applicable net namespace
@@ -6293,19 +6323,6 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 }
 EXPORT_SYMBOL(napi_complete_done);
 
-/* must be called under rcu_read_lock(), as we dont take a reference */
-struct napi_struct *napi_by_id(unsigned int napi_id)
-{
-	unsigned int hash = napi_id % HASH_SIZE(napi_hash);
-	struct napi_struct *napi;
-
-	hlist_for_each_entry_rcu(napi, &napi_hash[hash], napi_hash_node)
-		if (napi->napi_id == napi_id)
-			return napi;
-
-	return NULL;
-}
-
 static void skb_defer_free_flush(struct softnet_data *sd)
 {
 	struct sk_buff *skb, *next;