Function ether_gen_addr

freebsd/net/if_ethersubr.c:1441–1477

* Allocate an address from the FreeBSD Foundation OUI. This uses a * cryptographic hash function on the containing jail's name, UUID and the * interface name to attempt to provide a unique but stable address. * Pseudo-interfaces which require a MAC address should use this function to * allocate non-locally-administered addresses. */

 * allocate non-locally-administered addresses.
 */
void
ether_gen_addr(struct ifnet *ifp, struct ether_addr *hwaddr)
{
	SHA1_CTX ctx;
	char *buf;
	char uuid[HOSTUUIDLEN + 1];
	uint64_t addr;
	int i, sz;
	char digest[SHA1_RESULTLEN];
	char jailname[MAXHOSTNAMELEN];

	getcredhostuuid(curthread->td_ucred, uuid, sizeof(uuid));
	/* If each (vnet) jail would also have a unique hostuuid this would not
	 * be necessary. */
	getjailname(curthread->td_ucred, jailname, sizeof(jailname));
	sz = asprintf(&buf, M_TEMP, "%s-%s-%s", uuid, if_name(ifp),
	    jailname);
	if (sz < 0) {
		/* Fall back to a random mac address. */
		arc4rand(hwaddr, sizeof(*hwaddr), 0);
		hwaddr->octet[0] = 0x02;
		return;
	}

	SHA1Init(&ctx);
	SHA1Update(&ctx, buf, sz);
	SHA1Final(digest, &ctx);
	free(buf, M_TEMP);

	addr = ((digest[0] << 16) | (digest[1] << 8) | digest[2]) &
	    OUI_FREEBSD_GENERATED_MASK;
	addr = OUI_FREEBSD(addr);
	for (i = 0; i < ETHER_ADDR_LEN; ++i) {
		hwaddr->octet[i] = addr >> ((ETHER_ADDR_LEN - i - 1) * 8) &
		    0xFF;
	}
}

DECLARE_MODULE(ether, ether_mod, SI_SUB_INIT_IF, SI_ORDER_ANY);
MODULE_VERSION(ether, 1);