From: Lev Stipakov <l...@openvpn.net>
This patch provides additional information, such as
source address/port and destination address/port, to a
"recursive routing" warning message. It also mentiones
possible workaround.
Trac #843
Signed-off-by: Lev Stipakov <l...@openvpn.net>
---
v4:
- remove unneeded format specifier for const string
v3:
- factor out ports extraction code into own function
to avoid code duplication
- better commit message
v2:
- print protocol, source/dest addresses and ports
- mention "--allow-recursive-routing"
- add possible usecase to manpage
doc/openvpn.8 | 4 ++-
src/openvpn/forward.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 93 insertions(+), 9 deletions(-)
diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 94b5cc4..fb9eb84 100644
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4090,7 +4090,9 @@ notifications unless this option is enabled.
.TP
.B \-\-allow\-recursive\-routing
When this option is set, OpenVPN will not drop incoming tun packets
-with same destination as host.
+with same destination as host. Could be useful when packets sent by openvpn
+itself are not subject to the routing tables that would move packets
+into the tunnel.
.\"*********************************************************
.SS Data Channel Encryption Options:
These options are meaningful for both Static & TLS\-negotiated key modes
diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index f8faa81..e96c546 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -1291,10 +1291,42 @@ read_incoming_tun(struct context *c)
perf_pop();
}
+/*
+ * Extracts sport and dport from packet, used
+ * in recursive routing warning.
+ */
+static void
+extract_sport_dport(const struct buffer *buf, uint8_t protocol, int
offset_to_payload, int packet_len, uint16_t *sport, uint16_t *dport)
+{
+ /* whole packet? */
+ if (BLEN(buf) == packet_len)
+ {
+ const uint8_t *payload = BPTR(buf) + offset_to_payload;
+
+ if (protocol == OPENVPN_IPPROTO_UDP)
+ {
+ const struct openvpn_udphdr *udp = (const struct openvpn_udphdr
*)payload;
+ *sport = ntohs(udp->source);
+ *dport = ntohs(udp->dest);
+ }
+ else if (protocol == OPENVPN_IPPROTO_TCP)
+ {
+ const struct openvpn_tcphdr *tcp = (const struct openvpn_tcphdr
*)payload;
+ *sport = ntohs(tcp->source);
+ *dport = ntohs(tcp->dest);
+ }
+ }
+ else
+ {
+ *sport = 0;
+ *dport = 0;
+ }
+}
+
/**
* Drops UDP packets which OS decided to route via tun.
*
- * On Windows and OS X when netwotk adapter is disabled or
+ * On Windows and OS X when network adapter is disabled or
* disconnected, platform starts to use tun as external interface.
* When packet is sent to tun, it comes to openvpn, encapsulated
* and sent to routing table, which sends it again to tun.
@@ -1306,6 +1338,11 @@ drop_if_recursive_routing(struct context *c, struct
buffer *buf)
struct openvpn_sockaddr tun_sa;
int ip_hdr_offset = 0;
+ uint32_t saddr, daddr;
+ struct in6_addr saddr6, daddr6;
+ uint16_t sport, dport;
+ uint8_t protocol;
+
if (c->c2.to_link_addr == NULL) /* no remote addr known */
{
return;
@@ -1320,7 +1357,7 @@ drop_if_recursive_routing(struct context *c, struct
buffer *buf)
const struct openvpn_iphdr *pip;
/* make sure we got whole IP header */
- if (BLEN(buf) < ((int) sizeof(struct openvpn_iphdr) + ip_hdr_offset))
+ if (BLEN(buf) < ((int)sizeof(struct openvpn_iphdr) + ip_hdr_offset))
{
return;
}
@@ -1331,12 +1368,21 @@ drop_if_recursive_routing(struct context *c, struct
buffer *buf)
return;
}
- pip = (struct openvpn_iphdr *) (BPTR(buf) + ip_hdr_offset);
+ pip = (const struct openvpn_iphdr *)(BPTR(buf) + ip_hdr_offset);
- /* drop packets with same dest addr as gateway */
+ /* drop packets with the same dest addr as gateway */
if (tun_sa.addr.in4.sin_addr.s_addr == pip->daddr)
{
drop = true;
+
+ /* collect information for warning message */
+
+ saddr = ntohl(pip->saddr);
+ daddr = ntohl(pip->daddr);
+ protocol = pip->protocol;
+
+ extract_sport_dport(buf, protocol, ip_hdr_offset + sizeof(struct
openvpn_iphdr),
+ ip_hdr_offset + (int)(ntohs(pip->tot_len)),
&sport, &dport);
}
}
else if (proto_ver == 6)
@@ -1344,7 +1390,7 @@ drop_if_recursive_routing(struct context *c, struct
buffer *buf)
const struct openvpn_ipv6hdr *pip6;
/* make sure we got whole IPv6 header */
- if (BLEN(buf) < ((int) sizeof(struct openvpn_ipv6hdr) + ip_hdr_offset))
+ if (BLEN(buf) < ((int)sizeof(struct openvpn_ipv6hdr) + ip_hdr_offset))
{
return;
}
@@ -1355,22 +1401,58 @@ drop_if_recursive_routing(struct context *c, struct
buffer *buf)
return;
}
- /* drop packets with same dest addr as gateway */
+ /* drop packets with the same dest addr as gateway */
pip6 = (struct openvpn_ipv6hdr *) (BPTR(buf) + ip_hdr_offset);
if (IN6_ARE_ADDR_EQUAL(&tun_sa.addr.in6.sin6_addr, &pip6->daddr))
{
drop = true;
+
+ /* collect information for warning message */
+
+ saddr6 = pip6->saddr;
+ daddr6 = pip6->daddr;
+ protocol = pip6->nexthdr;
+
+ extract_sport_dport(buf, protocol, ip_hdr_offset + sizeof(struct
openvpn_ipv6hdr),
+ (int)sizeof(struct openvpn_ipv6hdr) +
ip_hdr_offset + (int)ntohs(pip6->payload_len),
+ &sport, &dport);
}
}
if (drop)
{
struct gc_arena gc = gc_new();
+ struct buffer addrs_buf = alloc_buf_gc(128, &gc);
+ /* drop packet */
c->c2.buf.len = 0;
- msg(D_LOW, "Recursive routing detected, drop tun packet to %s",
- print_link_socket_actual(c->c2.to_link_addr, &gc));
+ if (protocol == OPENVPN_IPPROTO_UDP)
+ {
+ buf_printf(&addrs_buf, "UDP");
+ }
+ else if (protocol == OPENVPN_IPPROTO_TCP)
+ {
+ buf_printf(&addrs_buf, "TCP");
+ }
+ else
+ {
+ buf_printf(&addrs_buf, "%d", protocol);
+ }
+
+ if (proto_ver == 4)
+ {
+ buf_printf(&addrs_buf, " %s:%d -> %s:%d",
+ print_in_addr_t(saddr, 0, &gc), sport,
+ print_in_addr_t(daddr, 0, &gc), dport);
+ } else if (proto_ver == 6)
+ {
+ buf_printf(&addrs_buf, " %s:%d -> %s:%d",
+ print_in6_addr(saddr6, 0, &gc), sport,
+ print_in6_addr(daddr6, 0, &gc), dport);
+ }
+
+ msg(D_LOW, "Recursive routing detected, drop packet %s. Fix your
routing or consider using --allow-recursive-routing option.", BSTR(&addrs_buf));
gc_free(&gc);
}
}
--
2.7.4
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