From cb3649cda6826684edf6c9faf70d56a276ca991e Mon Sep 17 00:00:00 2001
From: Eric Long <i@hack3r.moe>
Date: Tue, 8 Oct 2024 19:55:38 +0800
Subject: [PATCH] bpf: move random padding into function

---
 bpf/egress.c  | 3 +--
 bpf/ingress.c | 4 +---
 common/defs.h | 4 ++++
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/bpf/egress.c b/bpf/egress.c
index a209f3c..419a992 100644
--- a/bpf/egress.c
+++ b/bpf/egress.c
@@ -129,8 +129,7 @@ int egress_handler(struct __sk_buff* skb) {
   if (likely(conn->state == CONN_ESTABLISHED)) {
     seq = conn->seq;
     ack_seq = conn->ack_seq;
-    padding =
-      conn->settings.padding == PADDING_RANDOM ? (seq + ack_seq) % 11 : conn->settings.padding;
+    padding = conn_padding(conn, seq, ack_seq);
     conn->seq += payload_len + padding;
   } else {
     if (conn->state == CONN_IDLE) {
diff --git a/bpf/ingress.c b/bpf/ingress.c
index 63d07bb..effabcd 100644
--- a/bpf/ingress.c
+++ b/bpf/ingress.c
@@ -305,9 +305,7 @@ int ingress_handler(struct xdp_md* xdp) {
   }
   if (will_drop) return XDP_DROP;
 
-  __u32 padding = conn->settings.padding == PADDING_RANDOM
-                    ? (ntohl(tcp->seq) + ntohl(tcp->ack_seq)) % 11
-                    : conn->settings.padding;
+  __u32 padding = conn_padding(conn, ntohl(tcp->seq), ntohl(tcp->ack));
   size_t reserve_len = TCP_UDP_HEADER_DIFF + padding;
   if (ipv4) {
     __be16 old_len = ipv4->tot_len;
diff --git a/common/defs.h b/common/defs.h
index d1ac961..8811cee 100644
--- a/common/defs.h
+++ b/common/defs.h
@@ -307,6 +307,10 @@ static __always_inline __u32 conn_cooldown_display(struct connection* conn) {
   return conn->initiator ? conn_cooldown(conn) : 0;
 }
 
+static __always_inline __u32 conn_padding(struct connection* conn, __u32 seq, __u32 ack_seq) {
+  return conn->settings.padding == PADDING_RANDOM ? (seq + ack_seq) % 11 : conn->settings.padding;
+}
+
 static __always_inline int time_diff_sec(__u64 a, __u64 b) {
   if (a <= b) return 0;
   if ((a - b) % SECOND < SECOND / 2)