From 78894e78885cd27878029f0999354d516f24a8c9 Mon Sep 17 00:00:00 2001
From: Herbert Wolverson <herberticus@gmail.com>
Date: Mon, 18 Nov 2024 09:19:43 -0600
Subject: [PATCH] This should allow IS-IS packets to pass.

---
 src/rust/lqos_sys/src/bpf/common/dissector.h    |  4 ++--
 src/rust/lqos_sys/src/bpf/common/dissector_tc.h | 13 +++++++------
 src/rust/lqos_sys/src/bpf/lqos_kern.c           |  5 ++++-
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/rust/lqos_sys/src/bpf/common/dissector.h b/src/rust/lqos_sys/src/bpf/common/dissector.h
index 1e65e651..a827fee4 100644
--- a/src/rust/lqos_sys/src/bpf/common/dissector.h
+++ b/src/rust/lqos_sys/src/bpf/common/dissector.h
@@ -159,8 +159,8 @@ static __always_inline bool dissector_find_l3_offset(
         return true;
     }
 
-    // Fast return for ARP or non-802.3 ether types
-    if (eth_type == ETH_P_ARP || eth_type < ETH_P_802_3_MIN)
+    // Fast return for ARP or non-802.3 ether types (0xFEFE is IS-IS)
+    if (eth_type == ETH_P_ARP || eth_type < ETH_P_802_3_MIN || eth_type == 0xFEFE)
     {
         return false;
     }
diff --git a/src/rust/lqos_sys/src/bpf/common/dissector_tc.h b/src/rust/lqos_sys/src/bpf/common/dissector_tc.h
index 5074085a..a3577014 100644
--- a/src/rust/lqos_sys/src/bpf/common/dissector_tc.h
+++ b/src/rust/lqos_sys/src/bpf/common/dissector_tc.h
@@ -77,6 +77,13 @@ static __always_inline bool tc_dissector_find_l3_offset(
     __u32 offset = sizeof(struct ethhdr);
     __u16 eth_type = bpf_ntohs(dissector->ethernet_header->h_proto);
 
+    // Fast return for ARP or non-802.3 ether types/
+    // 0xFEFE is the ethertype used to ISIS
+    if (eth_type == ETH_P_ARP || eth_type < ETH_P_802_3_MIN || eth_type == 0xFEFE)
+    {
+        return false;
+    }
+
     // Fast return for unwrapped IP
     if (eth_type == ETH_P_IP || eth_type == ETH_P_IPV6)
     {
@@ -85,12 +92,6 @@ static __always_inline bool tc_dissector_find_l3_offset(
         return true;
     }
 
-    // Fast return for ARP or non-802.3 ether types
-    if (eth_type == ETH_P_ARP || eth_type < ETH_P_802_3_MIN)
-    {
-        return false;
-    }
-
     // Walk the headers until we find IP
     __u8 i = 0;
     while (i < 10 && !is_ip(eth_type))
diff --git a/src/rust/lqos_sys/src/bpf/lqos_kern.c b/src/rust/lqos_sys/src/bpf/lqos_kern.c
index 9dca16d7..65174da8 100644
--- a/src/rust/lqos_sys/src/bpf/lqos_kern.c
+++ b/src/rust/lqos_sys/src/bpf/lqos_kern.c
@@ -107,7 +107,7 @@ int xdp_prog(struct xdp_md *ctx)
     bpf_debug("(XDP) Scan VLANs: %u %u", internet_vlan, isp_vlan);
 #endif
     // If the dissector is unable to figure out what's going on, bail
-    // out.
+    // out. This specifically permits non-IP packets to pass unmolested.
     if (!dissector_new(ctx, &dissector)) return XDP_PASS;
 
     // Note that this step rewrites the VLAN tag if redirection
@@ -308,6 +308,9 @@ int tc_iphash_to_cpu(struct __sk_buff *skb)
     // we probably don't want to drop it - to ensure that IS-IS, ARP, STP
     // and other packet types are still handled by the default queues.
     struct tc_dissector_t dissector = {0};
+    // If the dissector returns false, return TC_ACT_OK to pass the packet
+    // unmolested/unshaped. This is designed to pass STP and similar non-IP
+    // traffic.
     if (!tc_dissector_new(skb, &dissector)) return TC_ACT_OK;
     if (!tc_dissector_find_l3_offset(&dissector)) return TC_ACT_OK;
     if (!tc_dissector_find_ip_header(&dissector)) return TC_ACT_OK;