This can be used to redirect all IPv6 traffic to the tun interface,
effectively black holing the IPv6 traffic. Without ICMPv6 error
messages this will result in timeouts when the server does not send
error codes. block-ipv6 allows client side only blocking on all
platforms that OpenVPN supports IPv6. On Android it is only way to do
sensible IPv6 blocking on Android < 5.0 and broken devices (Samsung).
PATCH V3:
- Fix style iusses reported by Antonio and accidentily commited parts
- merge udp_checksum and ipv6_checkusm into common ip_checksum method
- Use fake ff80::7 address when no other address is configured.
- Make block-ipv6 also work for server by replying block-ipv6 to all
ipv6 traffic send to the server
Note for the server the process_ip happens before the ipv6 route
lookup so every ipv6 packet, regardless of its source address is
replyied to with a no route to host packet.
---
doc/openvpn.8 | 34 +++++++++++++
src/openvpn/dhcp.c | 49 ++-----------------
src/openvpn/forward.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++--
src/openvpn/forward.h | 4 +-
src/openvpn/multi.c | 2 +-
src/openvpn/options.c | 11 +++++
src/openvpn/options.h | 1 +
src/openvpn/proto.c | 45 +++++++++++++++++
src/openvpn/proto.h | 52 ++++++++++++++++++++
src/openvpn/socket.h | 19 --------
10 files changed, 278 insertions(+), 71 deletions(-)
diff --git a/doc/openvpn.8 b/doc/openvpn.8
index a4189ac2..9f5ae781 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -1232,6 +1232,40 @@ Like \-\-redirect\-gateway, but omit actually changing
the default
gateway. Useful when pushing private subnets.
.\"*********************************************************
.TP
+.B \-\-block\-ipv6
+On the client, instead of sending IPv6 packets over the VPN tunnel, all IPv6
packets are answered with
+an ICMPv6 no route host message. On the server, all IPv6 packets from clients
are answered with an ICMPv6
+no route to host message. This options is intended for
+cases when IPv6 should be blocked and other options are not available.
+\.B \-\-block\-ipv6
+will use the remote IPv6 as source address of the ICMPv6 packets if set,
+otherwise will use fe80::7 as source address.
+
+For this option to make sense you actually have to route traffic to the tun
interface.
+Following config block would send all IPv6 traffic to OpenVPN and answer all
+requests with no route to host, effectively blocking IPv6.
+
+# client config
+.br
+.B \-\-ifconfig-ipv6
+fd15:53b6:dead::2/64 fd15:53b6:dead::1
+.br
+.B \-\-redirect\-gateway
+ipv6
+.br
+.B \-\-block\-ipv6
+
+# Server config, push a "valid" ipv6 config to the client and block on the
server
+.br
+.B \-\-push
+"ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
+.br
+.B \-\-push
+"redirect\-gateway ipv6"
+.br
+.B \-\-block\-ipv6
+.\"*********************************************************
+.TP
.B \-\-tun\-mtu n
Take the TUN device MTU to be
.B n
diff --git a/src/openvpn/dhcp.c b/src/openvpn/dhcp.c
index a2a54540..cec38cd6 100644
--- a/src/openvpn/dhcp.c
+++ b/src/openvpn/dhcp.c
@@ -147,49 +147,6 @@ do_extract(struct dhcp *dhcp, int optlen)
return ret;
}
-static uint16_t
-udp_checksum(const uint8_t *buf,
- const int len_udp,
- const uint8_t *src_addr,
- const uint8_t *dest_addr)
-{
- uint16_t word16;
- uint32_t sum = 0;
- int i;
-
- /* make 16 bit words out of every two adjacent 8 bit words and */
- /* calculate the sum of all 16 bit words */
- for (i = 0; i < len_udp; i += 2)
- {
- word16 = ((buf[i] << 8) & 0xFF00) + ((i + 1 < len_udp) ? (buf[i+1] &
0xFF) : 0);
- sum += word16;
- }
-
- /* add the UDP pseudo header which contains the IP source and destination
addresses */
- for (i = 0; i < 4; i += 2)
- {
- word16 = ((src_addr[i] << 8) & 0xFF00) + (src_addr[i+1] & 0xFF);
- sum += word16;
- }
- for (i = 0; i < 4; i += 2)
- {
- word16 = ((dest_addr[i] << 8) & 0xFF00) + (dest_addr[i+1] & 0xFF);
- sum += word16;
- }
-
- /* the protocol number and the length of the UDP packet */
- sum += (uint16_t) OPENVPN_IPPROTO_UDP + (uint16_t) len_udp;
-
- /* keep only the last 16 bits of the 32 bit calculated sum and add the
carries */
- while (sum >> 16)
- {
- sum = (sum & 0xFFFF) + (sum >> 16);
- }
-
- /* Take the one's complement of sum */
- return ((uint16_t) ~sum);
-}
-
in_addr_t
dhcp_extract_router_msg(struct buffer *ipbuf)
{
@@ -210,10 +167,10 @@ dhcp_extract_router_msg(struct buffer *ipbuf)
/* recompute the UDP checksum */
df->udp.check = 0;
- df->udp.check = htons(udp_checksum((uint8_t *) &df->udp,
+ df->udp.check = htons(ip_checksum(AF_INET, (uint8_t *) &df->udp,
sizeof(struct openvpn_udphdr) +
sizeof(struct dhcp) + optlen,
- (uint8_t *)&df->ip.saddr,
- (uint8_t *)&df->ip.daddr));
+ (uint8_t *)&df->ip.saddr,
(uint8_t *)&df->ip.daddr,
+ OPENVPN_IPPROTO_UDP));
/* only return the extracted Router address if DHCPACK */
if (message_type == DHCPACK)
diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index 1b7455bb..36e0afe2 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -1198,7 +1198,7 @@ process_incoming_tun(struct context *c)
* The --passtos and --mssfix options require
* us to examine the IP header (IPv4 or IPv6).
*/
- process_ip_header(c, PIPV4_PASSTOS|PIP_MSSFIX|PIPV4_CLIENT_NAT,
&c->c2.buf);
+ process_ip_header(c,
PIPV4_PASSTOS|PIP_MSSFIX|PIPV4_CLIENT_NAT|PIPV6_IMCP_NOHOST_CLIENT, &c->c2.buf);
#ifdef PACKET_TRUNCATION_CHECK
/* if (c->c2.buf.len > 1) --c->c2.buf.len; */
@@ -1209,6 +1209,9 @@ process_incoming_tun(struct context *c)
&c->c2.n_trunc_pre_encrypt);
#endif
+ }
+ if (c->c2.buf.len > 0)
+ {
encrypt_sign(c, true);
}
else
@@ -1219,6 +1222,117 @@ process_incoming_tun(struct context *c)
gc_free(&gc);
}
+/**
+ * Forges a IPv6 ICMP with a no route to host error code from the IPv6 packet
in buf and sends it back via
+ * the tun device
+ */
+void
+ipv6_send_icmp_unreachable(struct context * c, struct buffer *buf, bool client)
+{
+#define ICMPV6LEN 1280
+ struct openvpn_icmp6hdr icmp6out;
+ CLEAR(icmp6out);
+
+ /*
+ * Get a buffer to the ip packet, is_ipv6 automatically forwards
+ * the buffer to the ip packet
+ */
+ struct buffer inputipbuf = *buf;
+
+ is_ipv6(TUNNEL_TYPE(c->c1.tuntap), &inputipbuf);
+
+ if (BLEN(&inputipbuf) < (int) sizeof(struct openvpn_ipv6hdr))
+ {
+ return;
+ }
+
+ const struct openvpn_ipv6hdr* pip6 = (struct openvpn_ipv6hdr *)
BPTR(&inputipbuf);
+
+ struct openvpn_ipv6hdr pip6out;
+
+ /* Copy version, traffic class, flow label from input packet */
+ pip6out = *pip6;
+
+ pip6out.version_prio = pip6->version_prio;
+ pip6out.daddr = pip6->saddr;
+
+ /* Use the Ipv6 remote address if we have one, otherwise use a fake one */
+ if (c->options.ifconfig_ipv6_remote)
+ inet_pton(AF_INET6, c->options.ifconfig_ipv6_remote, &pip6out.saddr);
+ else
+ inet_pton(AF_INET6, "fe80::7", &pip6out.saddr);
+
+ pip6out.nexthdr = OPENVPN_IPPROTO_ICMPV6;
+
+ /*
+ * The ICMPv6 unreachable code worked best in my tests with Windows, Linux
and Android (arne)
+ * Windows did not like the adminitively prohibited return code (no fast
fail)
+ */
+ icmp6out.icmp6_type = OPENVPN_ICMP6_DESTINATION_UNREACHABLE;
+ icmp6out.icmp6_code = OPENVPN_ICMP6_DU_NOROUTE;
+
+ int icmpheader_len = sizeof(struct openvpn_ipv6hdr) + sizeof(struct
openvpn_icmp6hdr);
+ int ethheader_len = sizeof(struct openvpn_ethhdr);
+ int totalheader_len = icmpheader_len;
+
+ if (TUNNEL_TYPE(c->c1.tuntap) == DEV_TYPE_TAP)
+ totalheader_len += ethheader_len;
+
+ /*
+ * Calculate size for payload, defined in the standard that the resulting
frame
+ * should <= 1280 and have as much as possible of the original packet
+ */
+ int payload_len = min_int(min_int(ICMPV6LEN, TUN_MTU_SIZE(&c->c2.frame) -
icmpheader_len), buf_len(&inputipbuf));
+
+ pip6out.payload_len = htons(sizeof(struct openvpn_icmp6hdr) + payload_len);
+
+ /* Construct the packet as outgoing packet back to the client */
+ struct buffer * outbuf;
+ if (client) {
+ c->c2.to_tun = c->c2.buffers->aux_buf;
+ outbuf = &(c->c2.to_tun);
+ } else {
+ c->c2.to_link = c->c2.buffers->aux_buf;
+ outbuf = &(c->c2.to_link);
+ }
+ ASSERT(buf_init(outbuf, totalheader_len));
+
+ /* Fill the end of the buffer with original packet */
+ ASSERT(buf_safe(outbuf, payload_len));
+ ASSERT(buf_copy_n(outbuf, &inputipbuf, payload_len));
+
+ /* ICMP Header, copy into buffer to allow checksum calculation */
+ ASSERT(buf_write_prepend(outbuf, &icmp6out, sizeof(struct
openvpn_icmp6hdr)));
+
+ /* Calculate checksum over the packet and write to header */
+ ((struct openvpn_icmp6hdr*) BPTR(outbuf))->icmp6_cksum =
+ htons (ip_checksum(AF_INET6, BPTR(outbuf), BLEN(outbuf), (const
uint8_t*) &pip6out.saddr,
+ (uint8_t*) &pip6out.daddr,
OPENVPN_IPPROTO_ICMPV6));
+
+ /* IPv6 Header */
+ ASSERT(buf_write_prepend(outbuf, &pip6out, sizeof(struct
openvpn_ipv6hdr)));
+
+ /*
+ * Working IPv6 block for TAP will also need the client to respond to IPv6
nd with
+ * its own (fake) adress
+ */
+ if (TUNNEL_TYPE(c->c1.tuntap) == DEV_TYPE_TAP)
+ {
+ if (BLEN(buf) < (int) sizeof (struct openvpn_ethhdr))
+ return;
+
+ const struct openvpn_ethhdr* orig_ethhdr = (struct openvpn_ethhdr *)
BPTR(buf);
+
+ /* Copy frametype and reverse source/destination for the response */
+ struct openvpn_ethhdr ethhdr;
+ memcpy(ethhdr.source, orig_ethhdr->dest, OPENVPN_ETH_ALEN);
+ memcpy(ethhdr.dest, orig_ethhdr->source, OPENVPN_ETH_ALEN);
+ ethhdr.proto = htons(OPENVPN_ETH_P_IPV6);
+ ASSERT(buf_write_prepend(outbuf, ðhdr, sizeof(struct
openvpn_ethhdr)));
+ }
+}
+
+
void
process_ip_header(struct context *c, unsigned int flags, struct buffer *buf)
{
@@ -1240,7 +1354,10 @@ process_ip_header(struct context *c, unsigned int flags,
struct buffer *buf)
{
flags &= ~PIPV4_EXTRACT_DHCP_ROUTER;
}
-
+ if (!c->options.block_ipv6)
+ {
+ flags &= ~(PIPV6_IMCP_NOHOST_CLIENT|PIPV6_IMCP_NOHOST_SERVER);
+ }
if (buf->len > 0)
{
/*
@@ -1275,7 +1392,7 @@ process_ip_header(struct context *c, unsigned int flags,
struct buffer *buf)
/* possibly do NAT on packet */
if ((flags & PIPV4_CLIENT_NAT) && c->options.client_nat)
{
- const int direction = (flags & PIPV4_OUTGOING) ?
CN_INCOMING : CN_OUTGOING;
+ const int direction = (flags & PIP_OUTGOING) ? CN_INCOMING
: CN_OUTGOING;
client_nat_transform(c->options.client_nat, &ipbuf,
direction);
}
/* possibly extract a DHCP router message */
@@ -1295,6 +1412,13 @@ process_ip_header(struct context *c, unsigned int flags,
struct buffer *buf)
{
mss_fixup_ipv6(&ipbuf,
MTU_TO_MSS(TUN_MTU_SIZE_DYNAMIC(&c->c2.frame)));
}
+ if (!(flags & PIP_OUTGOING) && (flags &
(PIPV6_IMCP_NOHOST_CLIENT|PIPV6_IMCP_NOHOST_SERVER)))
+ {
+ ipv6_send_icmp_unreachable(c, buf, (bool)(flags &
PIPV6_IMCP_NOHOST_CLIENT));
+ /* Drop the IPv6 packet */
+ buf->len=0;
+ }
+
}
}
}
@@ -1478,7 +1602,7 @@ process_outgoing_tun(struct context *c)
* The --mssfix option requires
* us to examine the IP header (IPv4 or IPv6).
*/
- process_ip_header(c,
PIP_MSSFIX|PIPV4_EXTRACT_DHCP_ROUTER|PIPV4_CLIENT_NAT|PIPV4_OUTGOING,
&c->c2.to_tun);
+ process_ip_header(c,
PIP_MSSFIX|PIPV4_EXTRACT_DHCP_ROUTER|PIPV4_CLIENT_NAT|PIP_OUTGOING,
&c->c2.to_tun);
if (c->c2.to_tun.len <= MAX_RW_SIZE_TUN(&c->c2.frame))
{
diff --git a/src/openvpn/forward.h b/src/openvpn/forward.h
index 9fde5a30..0fa4a31e 100644
--- a/src/openvpn/forward.h
+++ b/src/openvpn/forward.h
@@ -251,9 +251,11 @@ bool send_control_channel_string(struct context *c, const
char *str, int msgleve
#define PIPV4_PASSTOS (1<<0)
#define PIP_MSSFIX (1<<1) /* v4 and v6 */
-#define PIPV4_OUTGOING (1<<2)
+#define PIP_OUTGOING (1<<2)
#define PIPV4_EXTRACT_DHCP_ROUTER (1<<3)
#define PIPV4_CLIENT_NAT (1<<4)
+#define PIPV6_IMCP_NOHOST_CLIENT (1<<5)
+#define PIPV6_IMCP_NOHOST_SERVER (1<<6)
void process_ip_header(struct context *c, unsigned int flags, struct buffer
*buf);
diff --git a/src/openvpn/multi.c b/src/openvpn/multi.c
index 82a0b9d9..eeb7644a 100644
--- a/src/openvpn/multi.c
+++ b/src/openvpn/multi.c
@@ -2837,7 +2837,7 @@ multi_get_queue(struct mbuf_set *ms)
if (mbuf_extract_item(ms, &item)) /* cleartext IP packet */
{
- unsigned int pip_flags = PIPV4_PASSTOS;
+ unsigned int pip_flags = PIPV4_PASSTOS|PIPV6_IMCP_NOHOST_SERVER;
set_prefix(item.instance);
item.instance->context.c2.buf = item.buffer->buf;
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 641a26e2..d1b4f48c 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -226,6 +226,8 @@ static const char usage_message[] =
" Add 'bypass-dns' flag to similarly bypass tunnel for
DNS.\n"
"--redirect-private [flags]: Like --redirect-gateway, but omit actually
changing\n"
" the default gateway. Useful when pushing private
subnets.\n"
+ "--block-ipv6 : (client only) Instead sending IPv6 to the server
generate\n"
+ " ICMPv6 host unreachable messages.\n"
"--client-nat snat|dnat network netmask alias : on client add 1-to-1 NAT
rule.\n"
#ifdef ENABLE_PUSH_PEER_INFO
"--push-peer-info : (client only) push client info to server.\n"
@@ -2084,6 +2086,10 @@ options_postprocess_verify_ce(const struct options
*options, const struct connec
msg(M_USAGE, "--lladdr can only be used in --dev tap mode");
}
+ if (options->block_ipv6 && dev != DEV_TYPE_TUN)
+ {
+ msg(M_USAGE, "--block-ipv6 can be only used in --dev tun mode");
+ }
/*
* Sanity check on MTU parameters
*/
@@ -6360,6 +6366,11 @@ add_option(struct options *options,
#endif
options->routes->flags |= RG_ENABLE;
}
+ else if (streq(p[0], "block-ipv6") && !p[1])
+ {
+ VERIFY_PERMISSION(OPT_P_ROUTE);
+ options->block_ipv6 = true;
+ }
else if (streq(p[0], "remote-random-hostname") && !p[1])
{
VERIFY_PERMISSION(OPT_P_GENERAL);
diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index 496c1143..38e9e431 100644
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -340,6 +340,7 @@ struct options
bool route_delay_defined;
struct route_option_list *routes;
struct route_ipv6_option_list *routes_ipv6; /* IPv6 */
+ bool block_ipv6;
bool route_nopull;
bool route_gateway_via_dhcp;
bool allow_pull_fqdn; /* as a client, allow server to push a FQDN for
certain parameters */
diff --git a/src/openvpn/proto.c b/src/openvpn/proto.c
index 2cbea3ab..4cafdd31 100644
--- a/src/openvpn/proto.c
+++ b/src/openvpn/proto.c
@@ -98,6 +98,51 @@ is_ipv6(int tunnel_type, struct buffer *buf)
return is_ipv_X( tunnel_type, buf, 6 );
}
+
+uint16_t
+ip_checksum(const sa_family_t af, const uint8_t *payload, const int
len_payload, const uint8_t *src_addr,
+ const uint8_t *dest_addr, const int proto)
+{
+ uint32_t sum = 0;
+ int addr_len = (af == AF_INET) ? 4 : 16;
+
+ /*
+ * make 16 bit words out of every two adjacent 8 bit words and */
+ /* calculate the sum of all 16 bit words
+ */
+ for (int i = 0; i < len_payload; i += 2)
+ {
+ sum += (uint16_t) (((payload[i] << 8) & 0xFF00) + ((i + 1 <
len_payload) ? (payload[i + 1] & 0xFF) : 0));
+
+ }
+
+ /* add the pseudo header which contains the IP source and destination
addresses */
+ for (int i = 0; i < addr_len; i += 2)
+ {
+ sum += (uint16_t) ((src_addr[i] << 8) & 0xFF00) + (src_addr[i + 1] &
0xFF);
+
+ }
+ for (int i = 0; i < addr_len; i += 2)
+ {
+ sum += (uint16_t) ((dest_addr[i] << 8) & 0xFF00) + (dest_addr[i + 1] &
0xFF);
+ }
+
+ /* the length of the payload */
+ sum += (uint16_t) len_payload;
+
+ /* The next header or proto field*/
+ sum += (uint16_t) proto;
+
+ /* keep only the last 16 bits of the 32 bit calculated sum and add the
carries */
+ while (sum >> 16)
+ {
+ sum = (sum & 0xFFFF) + (sum >> 16);
+ }
+
+ /* Take the one's complement of sum */
+ return ((uint16_t) ~sum);
+}
+
#ifdef PACKET_TRUNCATION_CHECK
void
diff --git a/src/openvpn/proto.h b/src/openvpn/proto.h
index 57f25c90..afbd226b 100644
--- a/src/openvpn/proto.h
+++ b/src/openvpn/proto.h
@@ -98,6 +98,7 @@ struct openvpn_iphdr {
#define OPENVPN_IPPROTO_IGMP 2 /* IGMP protocol */
#define OPENVPN_IPPROTO_TCP 6 /* TCP protocol */
#define OPENVPN_IPPROTO_UDP 17 /* UDP protocol */
+#define OPENVPN_IPPROTO_ICMPV6 58 /* ICMPV6 protocol */
uint8_t protocol;
uint16_t check;
@@ -120,6 +121,24 @@ struct openvpn_ipv6hdr {
struct in6_addr daddr;
};
+/*
+ * ICMPv6 header
+ */
+struct openvpn_icmp6hdr {
+# define OPENVPN_ICMP6_DESTINATION_UNREACHABLE 1
+# define OPENVPN_ND_ROUTER_SOLICIT 133
+# define OPENVPN_ND_ROUTER_ADVERT 134
+# define OPENVPN_ND_NEIGHBOR_SOLICIT 135
+# define OPENVPN_ND_NEIGHBOR_ADVERT 136
+# define OPENVPN_ND_INVERSE_SOLICIT 141
+# define OPENVPN_ND_INVERSE_ADVERT 142
+ uint8_t icmp6_type;
+# define OPENVPN_ICMP6_DU_NOROUTE 0
+# define OPENVPN_ICMP6_DU_COMMUNICATION_PROHIBTED 1
+ uint8_t icmp6_code;
+ uint16_t icmp6_cksum;
+ uint8_t icmp6_dataun[4];
+};
/*
* UDP header
@@ -265,6 +284,39 @@ bool is_ipv4(int tunnel_type, struct buffer *buf);
bool is_ipv6(int tunnel_type, struct buffer *buf);
+static inline int
+af_addr_size(sa_family_t af)
+{
+ switch (af)
+ {
+ case AF_INET: return sizeof(struct sockaddr_in);
+
+ case AF_INET6: return sizeof(struct sockaddr_in6);
+
+ default:
+#if 0
+ /* could be called from socket_do_accept() with empty addr */
+ msg(M_ERR, "Bad address family: %d\n", af);
+ ASSERT(0);
+#endif
+ return 0;
+ }
+}
+
+/**
+ * Calculates an IP or IPv6 checksum with a pseudo header as required by TCP,
UDP and ICMPv6
+ * @param af Address family for which the checksum is calculated AF_INET or
AF_INET6
+ * @param payload the TCP, ICMPv6 or UDP packet
+ * @param len_payload length of payload
+ * @param src_addr Source address of the packet
+ * @param dest_addr Destination address of the packet
+ * @param proto next header or IP protocol of the packet
+ * @return calculated checksum in host order
+ */
+uint16_t
+ip_checksum(const sa_family_t af, const uint8_t *payload, const int
len_payload, const uint8_t *src_addr,
+ const uint8_t *dest_addr, const int proto);
+
#ifdef PACKET_TRUNCATION_CHECK
void ipv4_packet_size_verify(const uint8_t *data,
const int size,
diff --git a/src/openvpn/socket.h b/src/openvpn/socket.h
index 2d7f2187..9ccc9466 100644
--- a/src/openvpn/socket.h
+++ b/src/openvpn/socket.h
@@ -848,25 +848,6 @@ addr_inet4or6(struct sockaddr *addr)
int addr_guess_family(sa_family_t af,const char *name);
-static inline int
-af_addr_size(sa_family_t af)
-{
- switch (af)
- {
- case AF_INET: return sizeof(struct sockaddr_in);
-
- case AF_INET6: return sizeof(struct sockaddr_in6);
-
- default:
-#if 0
- /* could be called from socket_do_accept() with empty addr */
- msg(M_ERR, "Bad address family: %d\n", af);
- ASSERT(0);
-#endif
- return 0;
- }
-}
-
static inline bool
link_socket_actual_match(const struct link_socket_actual *a1, const struct
link_socket_actual *a2)
{
--
2.13.6 (Apple Git-96)
------------------------------------------------------------------------------
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