Merge branch 'net-flow-dissector-allow-explicit-passing-of-netns'

Florian Westphal says:

====================
net: flow dissector: allow explicit passing of netns

Change since last version:
 fix kdoc comment warning reported by kbuild robot, no other changes,
 thus retaining RvB tags from Eric and Willem.
 v1: https://lore.kernel.org/netdev/20240607083205.3000-1-fw@strlen.de/

Years ago flow dissector gained ability to delegate flow dissection
to a bpf program, scoped per netns.

The netns is derived from skb->dev, and if that is not available, from
skb->sk.  If neither is set, we hit a (benign) WARN_ON_ONCE().

This WARN_ON_ONCE can be triggered from netfilter.
Known skb origins are nf_send_reset and ipv4 stack generated IGMP
messages.

Lets allow callers to pass the current netns explicitly and make
nf_tables use those instead.

This targets net-next instead of net because the WARN is benign and this
is not a regression.
====================

Link: https://lore.kernel.org/r/20240608221057.16070-1-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/skbuff.h

@@ -1498,8 +1498,14 @@ __skb_set_sw_hash(struct sk_buff *skb, __u32 hash, bool is_l4)
 	__skb_set_hash(skb, hash, true, is_l4);
 }
 
-void __skb_get_hash(struct sk_buff *skb);
-u32 __skb_get_hash_symmetric(const struct sk_buff *skb);
+u32 __skb_get_hash_symmetric_net(const struct net *net, const struct sk_buff *skb);
+
+static inline u32 __skb_get_hash_symmetric(const struct sk_buff *skb)
+{
+	return __skb_get_hash_symmetric_net(NULL, skb);
+}
+
+void __skb_get_hash_net(const struct net *net, struct sk_buff *skb);
 u32 skb_get_poff(const struct sk_buff *skb);
 u32 __skb_get_poff(const struct sk_buff *skb, const void *data,
 		   const struct flow_keys_basic *keys, int hlen);
@@ -1578,10 +1584,18 @@ void skb_flow_dissect_hash(const struct sk_buff *skb,
 			   struct flow_dissector *flow_dissector,
 			   void *target_container);
 
+static inline __u32 skb_get_hash_net(const struct net *net, struct sk_buff *skb)
+{
+	if (!skb->l4_hash && !skb->sw_hash)
+		__skb_get_hash_net(net, skb);
+
+	return skb->hash;
+}
+
 static inline __u32 skb_get_hash(struct sk_buff *skb)
 {
 	if (!skb->l4_hash && !skb->sw_hash)
-		__skb_get_hash(skb);
+		__skb_get_hash_net(NULL, skb);
 
 	return skb->hash;
 }

net/core/flow_dissector.c

@@ -1845,22 +1845,23 @@ EXPORT_SYMBOL(make_flow_keys_digest);
 
 static struct flow_dissector flow_keys_dissector_symmetric __read_mostly;
 
-u32 __skb_get_hash_symmetric(const struct sk_buff *skb)
+u32 __skb_get_hash_symmetric_net(const struct net *net, const struct sk_buff *skb)
 {
 	struct flow_keys keys;
 
 	__flow_hash_secret_init();
 
 	memset(&keys, 0, sizeof(keys));
-	__skb_flow_dissect(NULL, skb, &flow_keys_dissector_symmetric,
+	__skb_flow_dissect(net, skb, &flow_keys_dissector_symmetric,
 			   &keys, NULL, 0, 0, 0, 0);
 
 	return __flow_hash_from_keys(&keys, &hashrnd);
 }
-EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);
+EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric_net);
 
 /**
- * __skb_get_hash: calculate a flow hash
+ * __skb_get_hash_net: calculate a flow hash
+ * @net: associated network namespace, derived from @skb if NULL
  * @skb: sk_buff to calculate flow hash from
  *
  * This function calculates a flow hash based on src/dst addresses
@@ -1868,18 +1869,24 @@ EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);
  * on success, zero indicates no valid hash.  Also, sets l4_hash in skb
  * if hash is a canonical 4-tuple hash over transport ports.
  */
-void __skb_get_hash(struct sk_buff *skb)
+void __skb_get_hash_net(const struct net *net, struct sk_buff *skb)
 {
 	struct flow_keys keys;
 	u32 hash;
 
+	memset(&keys, 0, sizeof(keys));
+
+	__skb_flow_dissect(net, skb, &flow_keys_dissector,
+			   &keys, NULL, 0, 0, 0,
+			   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+
 	__flow_hash_secret_init();
 
-	hash = ___skb_get_hash(skb, &keys, &hashrnd);
+	hash = __flow_hash_from_keys(&keys, &hashrnd);
 
 	__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
 }
-EXPORT_SYMBOL(__skb_get_hash);
+EXPORT_SYMBOL(__skb_get_hash_net);
 
 __u32 skb_get_hash_perturb(const struct sk_buff *skb,
 			   const siphash_key_t *perturb)

net/netfilter/nf_tables_trace.c

@@ -317,7 +317,7 @@ void nft_trace_init(struct nft_traceinfo *info, const struct nft_pktinfo *pkt,
 	net_get_random_once(&trace_key, sizeof(trace_key));
 
 	info->skbid = (u32)siphash_3u32(hash32_ptr(skb),
-					skb_get_hash(skb),
+					skb_get_hash_net(nft_net(pkt), skb),
 					skb->skb_iif,
 					&trace_key);
 }

net/netfilter/nft_hash.c

@@ -51,7 +51,8 @@ static void nft_symhash_eval(const struct nft_expr *expr,
 	struct sk_buff *skb = pkt->skb;
 	u32 h;
 
-	h = reciprocal_scale(__skb_get_hash_symmetric(skb), priv->modulus);
+	h = reciprocal_scale(__skb_get_hash_symmetric_net(nft_net(pkt), skb),
+			     priv->modulus);
 
 	regs->data[priv->dreg] = h + priv->offset;
 }