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#include "misc-rstfilter.h"
#include "util-malloc.h"
#include "siphash24.h"
#include <time.h>
struct ResetFilter
{
unsigned long long seed;
size_t bucket_count;
size_t bucket_mask;
unsigned counter;
unsigned char *buckets;
};
static size_t
next_pow2(size_t n)
{
size_t bit_count = 0;
/* Always have at least one bit */
if (n == 0)
return 1;
/* If already a power-of-two, then return that */
if ((n & (n - 1)) == 0)
return n;
/* Count the number of bits */
while (n != 0) {
n >>= 1;
bit_count += 1;
}
return (size_t)1 << (size_t)bit_count;
}
struct ResetFilter *
rstfilter_create(unsigned long long seed, size_t bucket_count)
{
struct ResetFilter *rf;
rf = CALLOC(1, sizeof(*rf));
rf->seed = seed;
rf->bucket_count = next_pow2(bucket_count);
rf->bucket_mask = rf->bucket_count - 1;
rf->buckets = CALLOC(rf->bucket_count/2, sizeof(*rf->buckets));
return rf;
}
void
rstfilter_destroy(struct ResetFilter *rf)
{
if (rf == NULL)
return;
free(rf->buckets);
free(rf);
}
int
rstfilter_is_filter(struct ResetFilter *rf,
ipaddress src_ip, unsigned src_port,
ipaddress dst_ip, unsigned dst_port)
{
uint64_t hash;
uint64_t input[5];
uint64_t key[2];
size_t index;
unsigned char *p;
int result = 0;
/*
* Setup the input
*/
switch (src_ip.version) {
case 4:
input[0] = src_ip.ipv4;
input[1] = src_port;
input[2] = dst_ip.ipv4;
input[3] = dst_port;
break;
case 6:
input[0] = src_ip.ipv6.hi;
input[1] = src_ip.ipv6.lo;
input[2] = dst_ip.ipv6.hi;
input[3] = dst_ip.ipv6.lo;
input[4] = src_port<<16 | dst_port;
break;
}
key[0] = rf->seed;
key[1] = rf->seed;
/*
* Grab the bucket
*/
hash = siphash24(input, sizeof(input), key);
index = hash & rf->bucket_mask;
/*
* Find the result (1=filterout, 0=sendrst)
*/
p = &rf->buckets[index/2];
if (index & 1) {
if ((*p & 0x0F) == 0x0F)
result = 1; /* filter out */
else
*p = (*p) + 0x01;
} else {
if ((*p & 0xF0) == 0xF0)
result = 1; /* filter out */
else
*p = (*p) + 0x10;
}
/*
* Empty a random bucket
*/
input[0] = (unsigned)hash;
input[1] = rf->counter++;
hash = siphash24(input, sizeof(input), key);
index = hash & rf->bucket_mask;
p = &rf->buckets[index/2];
if (index & 1) {
if ((*p & 0x0F))
*p = (*p) - 0x01;
} else {
if ((*p & 0xF0))
*p = (*p) - 0x10;
}
return result;
}
int
rstfilter_selftest(void)
{
struct ResetFilter *rf;
size_t i;
unsigned count_filtered = 0;
unsigned count_passed = 0;
ipaddress src;
ipaddress dst;
src.version = 4;
src.ipv4 = 1;
dst.version = 4;
dst.ipv4 = 3;
rf = rstfilter_create(time(0), 64);
/* Verify the first 15 packets pass the filter */
for (i=0; i<15; i++) {
int x;
x = rstfilter_is_filter(rf, src, 2, dst, 4);
if (x) {
fprintf(stderr, "[-] rstfilter failed, line=%u\n", __LINE__);
return 1;
}
}
/* Now run 10000 more times */
for (i=0; i<1000; i++) {
int x;
x = rstfilter_is_filter(rf, src, 2, dst, 4);
count_filtered += x;
count_passed += !x;
}
/* SOME must have passed, due to us emptying random buckets */
if (count_passed == 0) {
fprintf(stderr, "[-] rstfilter failed, line=%u\n", __LINE__);
return 1;
}
/* However, while some pass, the vast majority should be filtered */
if (count_passed > count_filtered/10) {
fprintf(stderr, "[-] rstfilter failed, line=%u\n", __LINE__);
return 1;
}
//printf("filtered=%u passed=%u\n", count_filtered, count_passed);
return 0;
}
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