143 lines
3.5 KiB
C
143 lines
3.5 KiB
C
// vim:sw=4:ts=4:et:
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/*
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* Copyright (C) 2021 Andrei Belov (@defanator on github)
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*
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*/
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <inttypes.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include <unistd.h>
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/* 16 octets in binary form + dots between octets + trailing zero */
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#define INET6_ADDRBINSTRLEN ((8 * 16) + (1 * 15) + 1UL)
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#ifndef INET6_ADDRSTRLEN
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#define INET6_ADDRSTRLEN sizeof("ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255")
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#endif
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char * sprintb(char *dst, void const * const ptr, size_t const size)
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{
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int i, j;
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char *dp = dst;
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unsigned char byte;
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unsigned char *b = (unsigned char*) ptr;
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for (i = size - 1; i >= 0; i--) {
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for (j = 7; j >= 0; j--) {
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byte = (b[i] >> j) & 1;
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*dp++ = byte ? '1' : '0';
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}
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}
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*dp = 0x0;
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return dst;
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}
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char * sprintb_addr6(char *dst, struct in6_addr *in6) {
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char *dp = dst;
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u_char *p = in6->s6_addr;
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int i;
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for (i = 0; i < 16; i++) {
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sprintb(dp, &p[i], sizeof(u_char));
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dp += 8;
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if (i < 15) *dp++ = '.';
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}
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return dst;
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}
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struct in6_addr ipv6_rand(char *net,uint8_t prefixlen)
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{
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int i, j, s;
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uint8_t bits, shift;
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u_char *addr, *mask;
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struct in6_addr addr6, mask6,rand6;
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//char straddr6[INET6_ADDRSTRLEN];
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//char binaddr6[INET6_ADDRBINSTRLEN];
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char *ip6net = net;
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if (inet_pton(AF_INET6, ip6net, &addr6) < 1) {
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printf("incorrect IPv6 address/net: \"%s\"\n", ip6net);
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exit(1);
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}
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addr = addr6.s6_addr;
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mask = mask6.s6_addr;
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shift = prefixlen;
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bits = 128 - shift;
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for (i = 0; i < 16; i++) {
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s = (shift > 8) ? 8 : shift;
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shift -= s;
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mask[i] = (u_char) (0xffu << (8 - s));
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if (addr[i] != (addr[i] & mask[i])) {
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addr[i] &= mask[i];
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}
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}
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//inet_ntop(AF_INET6, &addr6, straddr6, INET6_ADDRSTRLEN);
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//printf("network: %s/%d\n", straddr6, prefixlen);
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//inet_ntop(AF_INET6, &mask6, straddr6, INET6_ADDRSTRLEN);
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//printf("netmask: %s (free bits=%d)\n", straddr6, bits);
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//printf("%s\n", sprintb_addr6(binaddr6, &addr6));
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//printf("%s\n", sprintb_addr6(binaddr6, &mask6));
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//printf("----\n");
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srand(((unsigned) getpid() << 16) ^ time(NULL));
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uint32_t rv = rand();
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int k = 0;
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shift = bits;
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rand6 = addr6;
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addr = rand6.s6_addr;
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for (j = 15; j >= 0; j--) {
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s = (shift > 8) ? 8 : shift;
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shift -= s;
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addr[j] = addr[j] ^ ((addr[j] ^ rv) & ~mask[j]);
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if (shift == 0) break;
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rv >>= 8;
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/*
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* Note that the MSB of the first octet in random value rv
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* will always be 0 as RAND_MAX=0x7FFFFFFF, i.e. if we refresh
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* rv after using all the 4 octets from uint32_t, the leading
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* bit in octets 4, 8, 12, 16 in generated IPv6 address
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* will _always_ be 0.
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*
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* While it seems legit for e.g. ::ffff:0:0/96 (IPv4-mapped
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* addresses), there may be a better way of handling this
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* (e.g. refresh rv after using 3 of 4 octets or reverse
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* bits in first octet before applying).
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*
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*/
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//if (++k > 2) {
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if (++k > 3) {
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rv = rand();
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k = 0;
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}
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}
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//inet_ntop(AF_INET6, &rand6, straddr6, INET6_ADDRSTRLEN);
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//printf("%s [%s]\n", sprintb_addr6(binaddr6, &rand6), straddr6);
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return rand6;
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} |