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Quentin 2021-04-25 16:27:43 +02:00
parent 9e3488dcba
commit 1ee8439ed8
Signed by: quentin
GPG key ID: A98E9B769E4FF428
2 changed files with 136 additions and 6 deletions
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102
xdp/test.c Normal file
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@ -0,0 +1,102 @@
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <stdlib.h>
#include <stdio.h>
char pkt[]={0x04, 0xf0, 0x21, 0x65, 0x18, 0x12, 0x50, 0x9a, 0x4c,
0x24, 0x1a, 0x72, 0x08, 0x00, 0x45, 0x00, 0x00, 0x20,
0x37, 0xb5, 0x40, 0x00, 0x40, 0x11, 0x70, 0x86, 0xc0,
0xa8, 0x00, 0xad, 0xd4, 0x2f, 0xfd, 0x0c, 0x9e, 0x1e,
0x09, 0x44, 0x00, 0x0c, 0xfd, 0x72, 0x64, 0x64, 0x64,
0x0a};
char pkt2[] = { 0x04,0xf0,0x21,0x65,0x18,0x12,0x50,0x9a,0x4c,0x24,0x1a,0x72,0x08,0x00,0x45,0x00,0x00,0x4e,0xf7,0xb9,0x00,0x00,0x40,0x11,0xb1,0x80,0xc0,0xa8,0x00,0xad,0x08,0x08,0x08,0x08,0x95,0xa2,0x00,0x35,0x00,0x3a,0xd1,0xb0,0x4a,0x8d,0x01,0x20,0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x01,0x06,0x67,0x6f,0x6f,0x67,0x6c,0x65,0x02,0x66,0x72,0x00,0x00,0x01,0x00,0x01,0x00,0x00,0x29,0x10,0x00,0x00,0x00,0x00,0x00,0x00,0x0c,0x00,0x0a,0x00,0x08,0x32,0x1b,0xf3,0x55,0xed,0xd5,0xd5,0x6b };
char pkt3[] = { 0x50,0x9a,0x4c,0x24,0x1a,0x72,0x04,0xf0,0x21,0x65,0x18,0x12,0x08,0x00,0x45,0x00,0x00,0x64,0x7e,0x9c,0x40,0x00,0x40,0x11,0xfb,0xfe,0xc0,0xa8,0x00,0xfe,0xc0,0xa8,0x00,0xad,0x00,0x35,0xe6,0x4c,0x00,0x50,0x88,0x50,0xd1,0x70,0x81,0x80,0x00,0x01,0x00,0x01,0x00,0x00,0x00,0x01,0x0c,0x73,0x61,0x66,0x65,0x62,0x72,0x6f,0x77,0x73,0x69,0x6e,0x67,0x0a,0x67,0x6f,0x6f,0x67,0x6c,0x65,0x61,0x70,0x69,0x73,0x03,0x63,0x6f,0x6d,0x00,0x00,0x01,0x00,0x01,0xc0,0x0c,0x00,0x01,0x00,0x01,0x00,0x00,0x01,0x0d,0x00,0x04,0x8e,0xfa,0xba,0x8a,0x00,0x00,0x29,0x04,0xd0,0x00,0x00,0x00,0x00,0x00,0x00 };
char csDesired[] = { 0x38, 0xf1 };
// Checksum utilities
__attribute__((__always_inline__))
static inline __u16 csum_fold_helper(__u64 csum) {
int i;
#pragma unroll
for (i = 0; i < 4; i ++) {
if (csum >> 16)
csum = (csum & 0xffff) + (csum >> 16);
}
return ~csum;
}
// Update checksum following RFC 1624 (Eqn. 3): https://tools.ietf.org/html/rfc1624
// HC' = ~(~HC + ~m + m')
// Where :
// HC - old checksum in header
// HC' - new checksum in header
// m - old value
// m' - new value
__attribute__((__always_inline__))
static inline void update_csum(__u64 *csum, __be32 old_flag,__be32 new_flag ) {
// ~HC
*csum = ~*csum;
*csum = *csum & 0xffff;
// + ~m
__u32 tmp;
tmp = ~old_addr;
*csum += tmp;
// + m
*csum += new_addr;
// then fold and complement result !
*csum = csum_fold_helper(*csum);
}
int main(void) {
void *data = pkt3;
void *data_end = pkt3+114;
struct ethhdr *eth = data; //structure ethernet from if_ether.h
struct iphdr *ip = (struct iphdr*)(eth + 1);
printf("%#06x\n", bpf_ntohs(ip->check));
__u64 cs = iph->check;
update_csum(&cs, old_addr, new_addr);
iph->check = cs;
printf("new cs: %x\n", ip->check);
}
int main2(void) {
void *data = pkt2; //pkt;
void *data_end = pkt2+92;//pkt+46;
struct ethhdr *eth = data; //structure ethernet from if_ether.h
struct iphdr *ip = (struct iphdr*)(eth + 1);
// Check that our packet ethernet headers is big enough, ie. at least the size of Ethernet's fixed headers
if((void*)ip > data_end) {
printf("eth headers too short\n");
return EXIT_SUCCESS;
}
// Check that the ethernet header declares an IPv4 packet
if(eth->h_proto == bpf_htons(ETH_P_IP)) {
printf("this is an IPv4 packet according to ethernet headers\n");
// Check that the IP packet is big enough, ie. at least the size of IP's fixed headers
if((void*)(ip + 1) > data_end) {
printf("IPv4 headers are too short \n");
return EXIT_SUCCESS;
}
if(ip->protocol == IPPROTO_UDP) {
printf("Protocol is UDP, flags are %#06x\n", ip->frag_off);
printf("Total offset: %x\n", (void*)&(ip->frag_off) - data);
ip->frag_off |= bpf_htons(0x4000); //Set the DF flag to 1 -> 0b 0100 0000 0000 0000
printf("Protocol is UDP, flags are now %#06x\n", ip->frag_off);
}
}
}

40
xdp/xdp_udp.c
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@ -25,6 +25,32 @@
#define bpf_printk(fmt, ...) \
({ \
char ____fmt[] = fmt; \
bpf_trace_printk(____fmt, sizeof(____fmt), \
##__VA_ARGS__); \
})
static inline unsigned short checksum(unsigned short *buf, int bufsz) {
unsigned long sum = 0;
while (bufsz > 1) {
sum += *buf;
buf++;
bufsz -= 2;
}
if (bufsz == 1) {
sum += *(unsigned char *)buf;
}
sum = (sum & 0xffff) + (sum >> 16);
sum = (sum & 0xffff) + (sum >> 16);
return ~sum;
}
SEC("xdp_udp")
int xdp_udp_func(struct xdp_md *ctx)
{
@ -32,25 +58,27 @@ int xdp_udp_func(struct xdp_md *ctx)
void *data = (void *)(long)ctx->data;
struct ethhdr *eth = data; //structure ethernet from if_ether.h
struct iphdr *ip = (struct iphdr*)(eth + 1);
// Check that our packet ethernet headers is big enough, ie. at least the size of Ethernet's fixed headers
if((void*)(eth + 1) > data_end) {
if((void*)ip > data_end) {
return XDP_PASS;
}
// Check that the ethernet header declares an IPv4 packet
if(eth->h_proto == bpf_htons(ETH_P_IP)) {
struct iphdr *ip = (struct iphdr*)(eth + 1);
// Check that the IP packet is big enough, ie. at least the size of IP's fixed headers
if((void*)(ip + 1) > data_end) {
if ((void*)(ip + 1) > data_end) {
return XDP_PASS;
}
if(ip->protocol == IPPROTO_UDP) {
ip->frag_off |= 0x4000; //Set the DF flag to 1 -> 0b 0100 0000 0000 0000
ip->frag_off |= bpf_htons(0x4000); //Set the DF flag to 1 -> 0b 0100 0000 0000 0000
ip->check = 0x0000;
ip->check = checksum((unsigned short*)ip, sizeof(ip));
}
}
return XDP_PASS;
}
char _license[] SEC("license") = "GPL";