[RFC PATCH net-next v5 1/4] flow_dissector: Add PPPoE dissectors

[Marcin Szycik <marcin.szycik@linux.intel.com>]

From: Wojciech Drewek <wojciech.drewek@intel.com>

Allow to dissect PPPoE specific fields which are:
- session ID (16 bits)
- ppp protocol (16 bits)
- type (16 bits) - this is PPPoE ethertype, for now only
  ETH_P_PPP_SES is supported, possible ETH_P_PPP_DISC
  in the future

The goal is to make the following TC command possible:

  # tc filter add dev ens6f0 ingress prio 1 protocol ppp_ses \
      flower \
        pppoe_sid 12 \
        ppp_proto ip \
      action drop

Note that only PPPoE Session is supported.

Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
---
v5: fix endianness when processing compressed protocols
v4:
  * pppoe header validation
  * added MPLS dissection
  * added support for compressed ppp protocol field
  * flow_dissector_key_pppoe::session_id stored in __be16
  * new field: flow_dissector_key_pppoe::type
v3: revert byte order changes in is_ppp_proto_supported from
    previous version
v2: ntohs instead of htons in is_ppp_proto_supported

 include/net/flow_dissector.h | 13 ++++++
 net/core/flow_dissector.c    | 85 +++++++++++++++++++++++++++++++++---
 2 files changed, 91 insertions(+), 7 deletions(-)

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index 0f9544a9bb9e..6c74812d64b2 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -277,6 +277,18 @@ struct flow_dissector_key_num_of_vlans {
 	u8 num_of_vlans;
 };
 
+/**
+ * struct flow_dissector_key_pppoe:
+ * @session_id: pppoe session id
+ * @ppp_proto: ppp protocol
+ * @type: pppoe eth type
+ */
+struct flow_dissector_key_pppoe {
+	__be16 session_id;
+	__be16 ppp_proto;
+	__be16 type;
+};
+
 enum flow_dissector_key_id {
 	FLOW_DISSECTOR_KEY_CONTROL, /* struct flow_dissector_key_control */
 	FLOW_DISSECTOR_KEY_BASIC, /* struct flow_dissector_key_basic */
@@ -307,6 +319,7 @@ enum flow_dissector_key_id {
 	FLOW_DISSECTOR_KEY_CT, /* struct flow_dissector_key_ct */
 	FLOW_DISSECTOR_KEY_HASH, /* struct flow_dissector_key_hash */
 	FLOW_DISSECTOR_KEY_NUM_OF_VLANS, /* struct flow_dissector_key_num_of_vlans */
+	FLOW_DISSECTOR_KEY_PPPOE, /* struct flow_dissector_key_pppoe */
 
 	FLOW_DISSECTOR_KEY_MAX,
 };
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 6aee04f75e3e..e3dfc9e5d095 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -895,6 +895,42 @@ bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
 	return result == BPF_OK;
 }
 
+/**
+ * is_ppp_proto_supported - checks if inner PPP protocol should be dissected
+ * @proto: protocol type (PPP proto field)
+ */
+static bool is_ppp_proto_supported(__be16 proto)
+{
+	switch (proto) {
+	case htons(PPP_AT):
+	case htons(PPP_IPX):
+	case htons(PPP_VJC_COMP):
+	case htons(PPP_VJC_UNCOMP):
+	case htons(PPP_MP):
+	case htons(PPP_COMPFRAG):
+	case htons(PPP_COMP):
+	case htons(PPP_IPCP):
+	case htons(PPP_ATCP):
+	case htons(PPP_IPXCP):
+	case htons(PPP_IPV6CP):
+	case htons(PPP_CCPFRAG):
+	case htons(PPP_MPLSCP):
+	case htons(PPP_LCP):
+	case htons(PPP_PAP):
+	case htons(PPP_LQR):
+	case htons(PPP_CHAP):
+	case htons(PPP_CBCP):
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool is_pppoe_ses_hdr_valid(struct pppoe_hdr hdr)
+{
+	return hdr.ver == 1 && hdr.type == 1 && hdr.code == 0;
+}
+
 /**
  * __skb_flow_dissect - extract the flow_keys struct and return it
  * @net: associated network namespace, derived from @skb if NULL
@@ -1214,26 +1250,61 @@ bool __skb_flow_dissect(const struct net *net,
 			struct pppoe_hdr hdr;
 			__be16 proto;
 		} *hdr, _hdr;
+		u16 ppp_proto;
+
 		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr);
 		if (!hdr) {
 			fdret = FLOW_DISSECT_RET_OUT_BAD;
 			break;
 		}
 
-		nhoff += PPPOE_SES_HLEN;
-		switch (hdr->proto) {
-		case htons(PPP_IP):
+		if (!is_pppoe_ses_hdr_valid(hdr->hdr)) {
+			fdret = FLOW_DISSECT_RET_OUT_BAD;
+			break;
+		}
+
+		/* least significant bit of the least significant octet
+		 * indicates if protocol field was compressed
+		 */
+		ppp_proto = ntohs(hdr->proto);
+		if (ppp_proto & 256) {
+			ppp_proto = htons(ppp_proto >> 8);
+			nhoff += PPPOE_SES_HLEN - 1;
+		} else {
+			ppp_proto = htons(ppp_proto);
+			nhoff += PPPOE_SES_HLEN;
+		}
+
+		if (ppp_proto == htons(PPP_IP)) {
 			proto = htons(ETH_P_IP);
 			fdret = FLOW_DISSECT_RET_PROTO_AGAIN;
-			break;
-		case htons(PPP_IPV6):
+		} else if (ppp_proto == htons(PPP_IPV6)) {
 			proto = htons(ETH_P_IPV6);
 			fdret = FLOW_DISSECT_RET_PROTO_AGAIN;
-			break;
-		default:
+		} else if (ppp_proto == htons(PPP_MPLS_UC)) {
+			proto = htons(ETH_P_MPLS_UC);
+			fdret = FLOW_DISSECT_RET_PROTO_AGAIN;
+		} else if (ppp_proto == htons(PPP_MPLS_MC)) {
+			proto = htons(ETH_P_MPLS_MC);
+			fdret = FLOW_DISSECT_RET_PROTO_AGAIN;
+		} else if (is_ppp_proto_supported(ppp_proto)) {
+			fdret = FLOW_DISSECT_RET_OUT_GOOD;
+		} else {
 			fdret = FLOW_DISSECT_RET_OUT_BAD;
 			break;
 		}
+
+		if (dissector_uses_key(flow_dissector,
+				       FLOW_DISSECTOR_KEY_PPPOE)) {
+			struct flow_dissector_key_pppoe *key_pppoe;
+
+			key_pppoe = skb_flow_dissector_target(flow_dissector,
+							      FLOW_DISSECTOR_KEY_PPPOE,
+							      target_container);
+			key_pppoe->session_id = hdr->hdr.sid;
+			key_pppoe->ppp_proto = ppp_proto;
+			key_pppoe->type = htons(ETH_P_PPP_SES);
+		}
 		break;
 	}
 	case htons(ETH_P_TIPC): {
-- 
2.35.1