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Added module which arbitrarily increases the size of the packet we received. Needs some tweaking to allow for modification of the header and payload fields yet, but the space allocation is already there. Also, multiple improvements overall

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h3xduck
2021-11-24 20:41:07 -05:00
parent 74cc7ff9e5
commit 442f955cf5
8 changed files with 592 additions and 269 deletions
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66
src/include/xdp/xdp_helper.h Normal file
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#ifndef __XDP_HELPER_H__
#define __XDP_HELPER_H__
#include <bpf/bpf_helpers.h>
#include "packet/protocol/ip_helper.h"
#include "packet/protocol/tcp_helper.h"
#include "packet/packet_manager.h"
static struct expand_return{
int code;
struct xdp_md ret_md;
void *data;
void *data_end;
struct ethhdr eth;
struct iphdr ip;
struct tcphdr tcp;
}expand_return;
/**
* Increases the packet payload reserved size by more_bytes bytes
* @param ctx XDP hook metadata
* @param eth start of ethernet header. Points inside ctx struct
* @param ip start of internet protocol header. Points inside ctx struct
* @param tcp start of tcp header. Points inside ctx struct
* @param more_bytes Number bytes to add
* @param
*/
static __always_inline struct expand_return expand_tcp_packet_payload(struct xdp_md *ctx, struct ethhdr *eth, struct iphdr *ip, struct tcphdr *tcp, int more_bytes){
//We might be able to reuse some data from old headers,
//but we will have to recompute checksums still
struct ethhdr eth_copy;
struct iphdr ip_copy;
struct tcphdr tcp_copy;
struct expand_return ret;
//Copy the header for later before expanding ctx
__builtin_memcpy(&eth_copy, eth, sizeof(struct ethhdr));
__builtin_memcpy(&ip_copy, ip, sizeof(struct iphdr));
__builtin_memcpy(&tcp_copy, tcp, sizeof(struct tcphdr));
if (bpf_xdp_adjust_tail(ctx, (int)(sizeof(char)*more_bytes)) != 0)
{
//Failed to expand
bpf_printk("Failed to expand a tcp packet reserved bytes by %i\n", more_bytes);
ret.code = -1;//The rest is undefined
return ret;
}
//We now have to readjust the packet headers, checksums have changed
//Note that we do not care about ctx->data_meta or any other extra field
//since we will not be using any communication here
__builtin_memcpy(&(ret.eth), &eth_copy, sizeof(struct ethhdr));
__builtin_memcpy(&(ret.ip), &ip_copy, sizeof(struct iphdr));
__builtin_memcpy(&(ret.tcp), &tcp_copy, sizeof(struct tcphdr));
ret.ret_md = *ctx;
ret.code = 0;
ret.data = (void *)(long)ctx->data;
ret.data_end = (void *)(long)ctx->data_end;
return ret;
}
#endif