[RFC bpf-next 3/7] net: plumb network namespace into __skb_flow_dissect

[Stanislav Fomichev <sdf@google.com>]

This new argument will be used in the next patches for the
eth_get_headlen use case. eth_get_headlen calls flow dissector
with only data (without skb) so there is currently no way to
pull attached BPF flow dissector program. With this new argument,
we can amend the callers to explicitly pass network namespace
so we can use attached BPF program.

Note: WARN_ON_ONCE(!net) will now trigger for eth_get_headlen users.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 include/linux/skbuff.h    | 15 +++++++++------
 net/core/flow_dissector.c | 20 +++++++++++---------
 net/ethernet/eth.c        |  5 +++--
 3 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 28723a86efdf..aa9a9983de80 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1227,7 +1227,8 @@ bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
 			    const struct sk_buff *skb,
 			    struct flow_dissector *flow_dissector,
 			    struct bpf_flow_keys *flow_keys);
-bool __skb_flow_dissect(const struct sk_buff *skb,
+bool __skb_flow_dissect(struct net *net,
+			const struct sk_buff *skb,
 			struct flow_dissector *flow_dissector,
 			void *target_container,
 			void *data, __be16 proto, int nhoff, int hlen,
@@ -1237,7 +1238,7 @@ static inline bool skb_flow_dissect(const struct sk_buff *skb,
 				    struct flow_dissector *flow_dissector,
 				    void *target_container, unsigned int flags)
 {
-	return __skb_flow_dissect(skb, flow_dissector, target_container,
+	return __skb_flow_dissect(NULL, skb, flow_dissector, target_container,
 				  NULL, 0, 0, 0, flags);
 }
 
@@ -1246,18 +1247,19 @@ static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
 					      unsigned int flags)
 {
 	memset(flow, 0, sizeof(*flow));
-	return __skb_flow_dissect(skb, &flow_keys_dissector, flow,
+	return __skb_flow_dissect(NULL, skb, &flow_keys_dissector, flow,
 				  NULL, 0, 0, 0, flags);
 }
 
 static inline bool
-skb_flow_dissect_flow_keys_basic(const struct sk_buff *skb,
+skb_flow_dissect_flow_keys_basic(struct net *net,
+				 const struct sk_buff *skb,
 				 struct flow_keys_basic *flow, void *data,
 				 __be16 proto, int nhoff, int hlen,
 				 unsigned int flags)
 {
 	memset(flow, 0, sizeof(*flow));
-	return __skb_flow_dissect(skb, &flow_keys_basic_dissector, flow,
+	return __skb_flow_dissect(net, skb, &flow_keys_basic_dissector, flow,
 				  data, proto, nhoff, hlen, flags);
 }
 
@@ -2438,7 +2440,8 @@ static inline void skb_probe_transport_header(struct sk_buff *skb,
 	if (skb_transport_header_was_set(skb))
 		return;
 
-	if (skb_flow_dissect_flow_keys_basic(skb, &keys, NULL, 0, 0, 0, 0))
+	if (skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
+					     NULL, 0, 0, 0, 0))
 		skb_set_transport_header(skb, keys.control.thoff);
 	else
 		skb_set_transport_header(skb, offset_hint);
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index bb1a54747d64..dddcc37c0462 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -725,6 +725,7 @@ bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
 
 /**
  * __skb_flow_dissect - extract the flow_keys struct and return it
+ * @net: associated network namespace, if NULL pulled from skb
  * @skb: sk_buff to extract the flow from, can be NULL if the rest are specified
  * @flow_dissector: list of keys to dissect
  * @target_container: target structure to put dissected values into
@@ -739,7 +740,8 @@ bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
  *
  * Caller must take care of zeroing target container memory.
  */
-bool __skb_flow_dissect(const struct sk_buff *skb,
+bool __skb_flow_dissect(struct net *net,
+			const struct sk_buff *skb,
 			struct flow_dissector *flow_dissector,
 			void *target_container,
 			void *data, __be16 proto, int nhoff, int hlen,
@@ -799,12 +801,11 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 
 		rcu_read_lock();
 
-		if (skb->dev)
-			attached = rcu_dereference(dev_net(skb->dev)->flow_dissector_prog);
-		else if (skb->sk)
-			attached = rcu_dereference(sock_net(skb->sk)->flow_dissector_prog);
-		else
-			WARN_ON_ONCE(1);
+		if (!net && skb)
+			net = skb_net(skb);
+		if (net)
+			attached = rcu_dereference(net->flow_dissector_prog);
+		WARN_ON_ONCE(!net);
 
 		if (attached) {
 			ret = __skb_flow_bpf_dissect(attached, skb,
@@ -1406,7 +1407,7 @@ u32 __skb_get_hash_symmetric(const struct sk_buff *skb)
 	__flow_hash_secret_init();
 
 	memset(&keys, 0, sizeof(keys));
-	__skb_flow_dissect(skb, &flow_keys_dissector_symmetric, &keys,
+	__skb_flow_dissect(NULL, skb, &flow_keys_dissector_symmetric, &keys,
 			   NULL, 0, 0, 0,
 			   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
 
@@ -1508,7 +1509,8 @@ u32 skb_get_poff(const struct sk_buff *skb)
 {
 	struct flow_keys_basic keys;
 
-	if (!skb_flow_dissect_flow_keys_basic(skb, &keys, NULL, 0, 0, 0, 0))
+	if (!skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
+					      NULL, 0, 0, 0, 0))
 		return 0;
 
 	return __skb_get_poff(skb, skb->data, &keys, skb_headlen(skb));
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 4c520110b04f..155d55025bfc 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -136,8 +136,9 @@ u32 eth_get_headlen(void *data, unsigned int len)
 		return len;
 
 	/* parse any remaining L2/L3 headers, check for L4 */
-	if (!skb_flow_dissect_flow_keys_basic(NULL, &keys, data, eth->h_proto,
-					      sizeof(*eth), len, flags))
+	if (!skb_flow_dissect_flow_keys_basic(NULL, NULL, &keys, data,
+					      eth->h_proto, sizeof(*eth),
+					      len, flags))
 		return max_t(u32, keys.control.thoff, sizeof(*eth));
 
 	/* parse for any L4 headers */
-- 
2.20.1.611.gfbb209baf1-goog