From: Christopher Martin <chrsmrtn@gmail.com>
Date: Tue, 16 Oct 2018 19:16:53 -0400
Subject: Adding option to randomize interface id

Please find attached a patch that adds a new feature to
wide-dhcpv6-client, namely an option ("ifid-random") in the
prefix-interface section of dhcp6c.conf to generate a random interface
id on startup. This is useful if you wish to have the final 64 bits of
your IPv6 address change from time to time - a sort of very rough
equivalent of IPv6 Privacy Extensions. If you do not add "ifid-random"
to the config file, then nothing about the client's current behaviour
changes.

Note that if your prefix-interface section has both the current "ifid
X" option (where X is whatever number you want to manually assign as
your interface id) and the new "ifid-random" option, then the
interface id is randomized and "ifid X" is ignored.

Thanks,
Christopher Martin
---
 cfparse.y     | 9 ++++++++-
 cftoken.l     | 1 +
 config.c      | 9 +++++++++
 config.h      | 2 +-
 dhcp6c.conf.5 | 9 +++++++++
 5 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/cfparse.y b/cfparse.y
index e83ecf7..9e685f4 100644
--- a/cfparse.y
+++ b/cfparse.y
@@ -104,7 +104,7 @@ static void cleanup_cflist __P((struct cf_list *));
 
 %token INTERFACE IFNAME
 %token PROFILE PROFILENAME
-%token PREFIX_INTERFACE SLA_ID SLA_LEN IFID DUID_ID
+%token PREFIX_INTERFACE SLA_ID SLA_LEN IFID IFID_RAND DUID_ID
 %token ID_ASSOC IA_PD IAID IA_NA
 %token ADDRESS
 %token REQUEST SEND ALLOW PREFERENCE
@@ -1064,6 +1064,13 @@ ifparam:
 			l->num = (u_int64_t)$2;
 			$$ = l;
 		}
+	|	IFID_RAND EOS
+		{
+			struct cf_list *l;
+
+			MAKE_CFLIST(l, IFPARAM_IFID_RAND, NULL, NULL);
+			$$ = l;
+		}
 	;
 
 ianaconf_list:
diff --git a/cftoken.l b/cftoken.l
index f35b59f..e266ac2 100644
--- a/cftoken.l
+++ b/cftoken.l
@@ -244,6 +244,7 @@ ecl		\}
 <S_CNF>sla-id { DECHO; return (SLA_ID); }
 <S_CNF>sla-len { DECHO; return (SLA_LEN); }
 <S_CNF>ifid { DECHO; return (IFID); }
+<S_CNF>ifid-random { DECHO; return (IFID_RAND); }
 
 	/* duration */
 <S_CNF>infinity { DECHO; return (INFINITY); }
diff --git a/config.c b/config.c
index 2c5ad5d..5829d92 100644
--- a/config.c
+++ b/config.c
@@ -521,6 +521,15 @@ add_pd_pif(iapdc, cfl0)
 			}
 			break;
 		case IFPARAM_IFID:
+			if (use_default_ifid) {
+				for (i = sizeof(pif->ifid) - 1; i >= 0; i--)
+					pif->ifid[i] = (cfl->num >> 8*(sizeof(pif->ifid) - 1 - i)) & 0xff;
+				use_default_ifid = 0;
+			}
+			break;
+		case IFPARAM_IFID_RAND:
+			for (i = 0; i < pif->ifid_len ; i++)
+				cfl->num = cfl->num*2 + rand()%2;
 			for (i = sizeof(pif->ifid) -1; i >= 0; i--)
 				pif->ifid[i] = (cfl->num >> 8*(sizeof(pif->ifid) - 1 - i)) & 0xff;
 			use_default_ifid = 0;
diff --git a/config.h b/config.h
index 64ce9e8..36a5aa3 100644
--- a/config.h
+++ b/config.h
@@ -266,7 +266,7 @@ enum { DECL_SEND, DECL_ALLOW, DECL_INFO_ONLY, DECL_REQUEST, DECL_DUID,
        DECL_PREFIX, DECL_PREFERENCE, DECL_SCRIPT, DECL_DELAYEDKEY,
        DECL_ADDRESS,
        DECL_RANGE, DECL_ADDRESSPOOL,
-       IFPARAM_SLA_ID, IFPARAM_SLA_LEN, IFPARAM_IFID,
+       IFPARAM_SLA_ID, IFPARAM_SLA_LEN, IFPARAM_IFID, IFPARAM_IFID_RAND,
        DHCPOPT_RAPID_COMMIT, DHCPOPT_AUTHINFO,
        DHCPOPT_DNS, DHCPOPT_DNSNAME,
        DHCPOPT_IA_PD, DHCPOPT_IA_NA, DHCPOPT_NTP,
diff --git a/dhcp6c.conf.5 b/dhcp6c.conf.5
index 1c91d72..5693fb8 100644
--- a/dhcp6c.conf.5
+++ b/dhcp6c.conf.5
@@ -453,6 +453,15 @@ must be a decimal integer.  It will be combined with the delegated
 prefix and the sla-id to form a complete interface address.  The
 default is to use the EUI-64 address of the
 .Ar interface .
+.It Xo
+.Ic ifid-random ;
+.Xc
+This statement instructs the client to generate a completely random
+interface id. This will override the
+.Ic ifid
+statement, if present. The resulting random interface id will be combined
+with the delegated prefix and the sla-id to form a complete interface
+address.
 .El
 .El
 .\"