netdev: prevent accessing NAPI instances from another namespace

JIRA: https://issues.redhat.com/browse/RHEL-77816
CVE: CVE-2025-21659
Upstream Status: net.git commit d1cacd7
Conflicts:
  - net/core/dev.h,
    conflict as we don't have upstream commits b9495b5 ("net:
    move kick_defer_list_purge() to net/core/dev.h"),
    ecefbc0 ("net: softnet_data: Make xmit per task"),
    2fe50a4 ("net: move dev_xmit_recursion() helpers to net/core/dev.h")

commit d1cacd7
Author: Jakub Kicinski <kuba@kernel.org>
Date:   Mon Jan 6 10:01:36 2025 -0800

    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: 1287c1a ("netdev-genl: Support setting per-NAPI config values")
    Fixes: 27f91aa ("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>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

net/core/dev.c

@@ -748,6 +748,36 @@ 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
@@ -6217,19 +6247,6 @@ 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;

net/core/dev.h

@@ -24,6 +24,8 @@ struct sd_flow_limit {
 
 extern int netdev_flow_limit_table_len;
 
+struct napi_struct *netdev_napi_by_id(struct net *net, unsigned int napi_id);
+
 #ifdef CONFIG_PROC_FS
 int __init dev_proc_init(void);
 #else
@@ -233,5 +235,4 @@ static inline void netdev_set_gro_flush_timeout(struct net_device *netdev,
 
 int rps_cpumask_housekeeping(struct cpumask *mask);
 
-struct napi_struct *napi_by_id(unsigned int napi_id);
 #endif

net/core/netdev-genl.c

@@ -165,8 +165,6 @@ netdev_nl_napi_fill_one(struct sk_buff *rsp, struct napi_struct *napi,
 	void *hdr;
 	pid_t pid;
 
-	if (WARN_ON_ONCE(!napi->dev))
-		return -EINVAL;
 	if (!(napi->dev->flags & IFF_UP))
 		return 0;
 
@@ -228,7 +226,7 @@ int netdev_nl_napi_get_doit(struct sk_buff *skb, struct genl_info *info)
 	rtnl_lock();
 	rcu_read_lock();
 
-	napi = napi_by_id(napi_id);
+	napi = netdev_napi_by_id(genl_info_net(info), napi_id);
 	if (napi) {
 		err = netdev_nl_napi_fill_one(rsp, napi, info);
 	} else {
@@ -337,7 +335,7 @@ int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
 	rtnl_lock();
 	rcu_read_lock();
 
-	napi = napi_by_id(napi_id);
+	napi = netdev_napi_by_id(genl_info_net(info), napi_id);
 	if (napi) {
 		err = netdev_nl_napi_set_config(napi, info);
 	} else {