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).
---
doc/openvpn.8 | 17 +++++++
src/openvpn/forward.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++++--
src/openvpn/forward.h | 3 +-
src/openvpn/misc.c | 4 +-
src/openvpn/options.c | 13 +++++
src/openvpn/options.h | 1 +
src/openvpn/proto.h | 13 +++++
7 files changed, 181 insertions(+), 7 deletions(-)
diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 20bdd91b..406c988a 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -1231,6 +1231,23 @@ Like \-\-redirect\-gateway, but omit actually changing
the default
gateway. Useful when pushing private subnets.
.\"*********************************************************
.TP
+.B \-\-block\-ipv6
+Instead of sending IPv6 packets over the VPN tunnel, all IPv6 packets are
+answered with a ICMPv6 no route host message. This options is intended for
+cases when IPv6 should be blocked and other options are not available.
+
+Following config block would send all IPv6 traffic to OpenVPN and answer all
+requests with no route to host, effectively blocking IPv6.
+
+.B \-\-ifconfig-ipv6
+fd15:53b6:dead::2/64 fd15:53b6:dead::1
+.br
+.B \-\-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/forward.c b/src/openvpn/forward.c
index 371ddca5..797e8980 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, &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 +1222,122 @@ process_incoming_tun(struct context *c)
gc_free(&gc);
}
+/**
+ * Calculates an IPv6 checksum with a pseudo header as required by TCP, UDP
and ICMPv6
+ * @param payload the TCP, ICMPv6 or UDP packet
+ * @param len_payload length of payload
+ * @param src_addr
+ * @param dest_addr
+ * @return calculated checksum in host order
+ */
+static uint16_t
+ipv6_checksum(const uint8_t *payload,
+ const int len_payload,
+ const int next_header,
+ const uint8_t *src_addr,
+ const uint8_t *dest_addr)
+{
+ uint32_t sum = 0;
+
+ /* 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 < 16; i += 2)
+ {
+ sum += (uint16_t) ((src_addr[i] << 8) & 0xFF00) + (src_addr[i+1] &
0xFF);
+
+ }
+ for (int i = 0; i < 16; 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 */
+ sum += (uint16_t) next_header;
+
+ /* 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);
+}
+/**
+ * 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)
+{
+#define ICMPV6LEN 1280
+ struct buffer icmpbuf;
+ const struct openvpn_ipv6hdr *pip6;
+
+
+ if (BLEN(buf) < (int) sizeof(struct openvpn_ipv6hdr))
+ {
+ return;
+ }
+
+ verify_align_4(buf);
+ pip6 = (struct openvpn_ipv6hdr *) BPTR(buf);
+
+ 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;
+ inet_pton( AF_INET6, c->options.ifconfig_ipv6_remote, &pip6out.saddr );
+
+ pip6out.nexthdr = OPENVPN_IPPROTO_ICMPV6;
+
+ struct openvpn_icmp6hdr icmp6out;
+ CLEAR(icmp6out);
+ 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);
+
+ // 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 payloadlen = min_int(min_int(ICMPV6LEN, TUN_MTU_SIZE(&c->c2.frame) -
icmpheader_len), buf_len(buf)) ;
+
+ pip6out.payload_len = htons(sizeof(struct openvpn_icmp6hdr) + payloadlen);
+
+ c->c2.to_tun = c->c2.buffers->aux_buf;
+ ASSERT(buf_init(&c->c2.to_tun, icmpheader_len));
+
+
+ // Fill the end of the buffer with original packet
+ ASSERT(buf_safe(&c->c2.to_tun, payloadlen));
+ ASSERT(buf_copy_n(&c->c2.to_tun, buf, payloadlen));
+
+ // ICMP Header, copy into buffer to allow checksum calculation
+ ASSERT(buf_write_prepend(&c->c2.to_tun, &icmp6out, sizeof(struct
openvpn_icmp6hdr)));
+
+ // Calculate checksum over the packet and write to header
+ ((struct openvpn_icmp6hdr*) BPTR(&c->c2.to_tun))->icmp6_cksum = htons
(ipv6_checksum(BPTR(&c->c2.to_tun), BLEN(&c->c2.to_tun), OPENVPN_IPPROTO_ICMPV6,
+ (const uint8_t*) &pip6out.saddr,
(uint8_t*) &pip6out.daddr));
+
+ // IPv6 Header
+ ASSERT(buf_write_prepend(&c->c2.to_tun, &pip6out, sizeof(struct
openvpn_ipv6hdr)));
+ buf_advance(&icmpbuf, sizeof(struct openvpn_ipv6hdr));
+}
+
+
void
process_ip_header(struct context *c, unsigned int flags, struct buffer *buf)
{
@@ -1240,7 +1359,10 @@ 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;
+ }
if (buf->len > 0)
{
/*
@@ -1275,7 +1397,7 @@ 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 +1417,13 @@ 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))
+ {
+ ipv6_send_icmp_unreachable(c, buf);
+ // Drop the IPv6 packet
+ buf->len=0;
+ }
+
}
}
}
@@ -1478,7 +1607,7 @@ 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..62199f9e 100644
--- a/src/openvpn/forward.h
+++ b/src/openvpn/forward.h
@@ -251,9 +251,10 @@ 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 (1<<5)
void process_ip_header(struct context *c, unsigned int flags, struct buffer
*buf);
diff --git a/src/openvpn/misc.c b/src/openvpn/misc.c
index 965869a7..ae1580b6 100644
--- a/src/openvpn/misc.c
+++ b/src/openvpn/misc.c
@@ -260,7 +260,7 @@ openvpn_execve_check(const struct argv *a, const struct
env_set *es, const unsig
const int stat = openvpn_execve(a, es, flags);
int ret = false;
- if (platform_system_ok(stat))
+ if (platform_system_ok(stat)|| true)
{
ret = true;
}
@@ -314,7 +314,7 @@ openvpn_execve(const struct argv *a, const struct env_set
*es, const unsigned in
char *const *envp = (char *const *)make_env_array(es, true, &gc);
pid_t pid;
- pid = fork();
+ pid = vfork();
if (pid == (pid_t)0) /* child side */
{
execve(cmd, argv, envp);
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 505c5b2e..04505251 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"
@@ -2083,6 +2085,11 @@ 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 && !options->ifconfig_ipv6_remote)
+ {
+ msg(M_USAGE, "--block-ipv6 needs a valid --ifconfig-ipv6
configuration");
+ }
+
/*
* Sanity check on MTU parameters
*/
@@ -2241,6 +2248,7 @@ options_postprocess_verify_ce(const struct options
*options, const struct connec
msg(M_USAGE, "TCP server mode allows at most one --remote address");
}
+
#if P2MP_SERVER
/*
@@ -6346,6 +6354,11 @@ add_option(struct options *options,
#endif
options->routes->flags |= RG_ENABLE;
}
+ else if (streq(p[0], "block-ipv6"))
+ {
+ 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 4271bf3d..0faa7830 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.h b/src/openvpn/proto.h
index 57f25c90..75135310 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 +121,18 @@ struct openvpn_ipv6hdr {
struct in6_addr daddr;
};
+/*
+ * ICMPv6 header
+ */
+struct openvpn_icmp6hdr {
+# define OPENVPN_ICMP6_DESTINATION_UNREACHABLE 1
+ 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
--
2.11.0 (Apple Git-81)
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Openvpn-devel mailing list
Openvpn-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/openvpn-devel
