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Arbitrary payload modification fully works now. Absolutely ridicous the time it took me (2 days) to realize I was computing the ip checksum with the old checksum values, which made it not to work. Finally can keep going

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h3xduck
2021-11-27 14:10:43 -05:00
parent ca23880fd4
commit a440326653
7 changed files with 814 additions and 802 deletions
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34
src/include/packet/protocol/ip_helper.h
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@@ -24,7 +24,7 @@ static __always_inline unsigned short checksum(unsigned short *addr, int nbytes)
if(nbytes>0){
sum +=htons((unsigned char)*addr);
}
while (sum>>16){
sum = (sum & 0xffff) + (sum >> 16);
}
@@ -34,30 +34,34 @@ static __always_inline unsigned short checksum(unsigned short *addr, int nbytes)
}
static __always_inline uint16_t csum_fold_helper(uint32_t csum)
static __always_inline __u16 csum_fold_helper(__u32 csum)
{
bpf_printk("csumA: %u\n", csum & 0xffff);
bpf_printk("csumB: %u\n", csum >> 16);
bpf_printk("csumA+B: %u\n", (csum & 0xffff) + (csum >> 16));
bpf_printk("csumNEG(A+B): %u\n", ~((csum & 0xffff) + (csum >> 16)));
//return ~((csum & 0xffff) + (csum >> 16));
//The following solves some errors where the last summatory overflows
#pragma unroll
for (int ii = 0; ii < 4; ii++) {
if (csum >> 16)
csum = (csum & 0xffff) + (csum >> 16);
for (int i = 0; i < 4; i ++) {
if (csum >> 16){
csum = (csum & 0xffff) + (csum >> 16);
}
}
return ~csum;
return ~csum;
}
/**
* IP checksum calculation.
* Following RFC 1071, using BPFs.*
*/
static __always_inline void ipv4_csum(void *data_start, int data_size, uint32_t *csum)
static __always_inline void ipv4_csum(void *data_start, int data_size, __u32 *csum)
{
bpf_printk("csum: %u\n", *csum);
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
bpf_printk("csum: %u\n", *csum);
//WITH EBPF HELPERS
bpf_printk("csum: %u for data_start %u, data_size %i\n", *csum, data_start, data_size);
unsigned char* p = (unsigned char*) data_start;
for(int ii = 0; ii<20; ii++){
bpf_printk("B%i: %x\n", ii, p[ii]);
}
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
*csum = csum_fold_helper(*csum);
bpf_printk("csum: %u\n", *csum);
}
#endif