Use kprobe to change checksum offset

hack3ric · Aug 8, 2024 · 1ecbc12 · 1ecbc12
1 parent c0d99b3
commit 1ecbc12
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Showing 2 changed files with 3 additions and 1 deletion.
diff --git a/bpf/egress.c b/bpf/egress.c
@@ -160,7 +160,7 @@ int egress_handler(struct __sk_buff* skb) {
   csum_diff = bpf_csum_diff((__be32*)&old_ph, sizeof(old_ph), (__be32*)&new_ph, sizeof(new_ph), 0);
   bpf_l4_csum_replace(skb, csum_off, 0, csum_diff, BPF_F_PSEUDO_HDR);
 
-  // bpf_skb_change_proto(skb, IPPROTO_TCP, MAGIC_FLAG);
+  bpf_skb_change_proto(skb, IPPROTO_TCP, MAGIC_FLAG);
   // log_info("%llu", retval);
   // mimic_change_csum_offset(skb, IPPROTO_TCP);
 

diff --git a/kmod/kprobe.c b/kmod/kprobe.c
@@ -41,6 +41,8 @@ static int ret_handler(struct kretprobe_instance* ri, struct pt_regs* regs) {
   struct bpf_skb_change_proto_params* params = (typeof(params))ri->data;
   if (!params->skb || params->flags != MAGIC_FLAG) return 0;
 
+  printk("checksum: %d\n", params->skb->ip_summed);
+
   if (params->skb->ip_summed != CHECKSUM_PARTIAL) {
     regs_set_return_value(regs, -1);
     return 0;