[RFC PATCH net-next v4 1/4] flow_dissector: Add PPPoE dissectors

Marcin Szycik
2022-07-08T12:25:00Z

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>
---
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 | 84 +++++++++++++++++++++++++++++++++---
2 files changed, 90 insertions(+), 7 deletions(-)

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index a4c6057c7097..af0d429b9a26 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -261,6 +261,18 @@ 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 */
@@ -291,6 +303,7 @@ 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..3a90219d2354 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 +1250,60 @@ bool __skb_flow_dissect(const struct net *net,
struct pppoe_hdr hdr;
__be16 proto;
} *hdr, _hdr;
+ __be16 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 first byte
+ * indicates if protocol field was compressed
+ */
+ if (hdr->proto & 1) {
+ ppp_proto = hdr->proto << 8;
+ nhoff += PPPOE_SES_HLEN - 1;
+ } else {
+ ppp_proto = hdr->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