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Tue, 29 May 2018 04:48:24 -0700 (PDT) From: Lev Stipakov X-Google-Original-From: Lev Stipakov To: openvpn-devel@lists.sourceforge.net Date: Tue, 29 May 2018 14:47:27 +0300 Message-Id: <1527594447-10710-1-git-send-email-lev@openvpn.net> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1527587707-21417-1-git-send-email-lev@openvpn.net> References: <1527587707-21417-1-git-send-email-lev@openvpn.net> X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (lstipakov[at]gmail.com) -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [74.125.82.68 listed in list.dnswl.org] -0.0 RCVD_IN_MSPIKE_H3 RBL: Good reputation (+3) [74.125.82.68 listed in wl.mailspike.net] -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.0 RCVD_IN_MSPIKE_WL Mailspike good senders X-Headers-End: 1fNd7A-005RwK-99 Subject: [Openvpn-devel] [PATCH v2] Improve "recursive routing" warning X-BeenThere: openvpn-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Lev Stipakov MIME-Version: 1.0 Errors-To: openvpn-devel-bounces@lists.sourceforge.net X-getmail-retrieved-from-mailbox: Inbox V2: style fixes - print protocol, source/dest addresses and ports - mention "--allow-recursive-routing" - add possible usecase to manpage Trac #843 Signed-off-by: Lev Stipakov style fixes --- doc/openvpn.8 | 4 ++- src/openvpn/forward.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 88 insertions(+), 9 deletions(-) diff --git a/doc/openvpn.8 b/doc/openvpn.8 index 4114f40..262d4ea 100644 --- a/doc/openvpn.8 +++ b/doc/openvpn.8 @@ -4072,7 +4072,9 @@ 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 7d9a338..b121849 100644 --- a/src/openvpn/forward.c +++ b/src/openvpn/forward.c @@ -1068,7 +1068,7 @@ read_incoming_tun(struct context *c) /** * 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. @@ -1080,6 +1080,11 @@ 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; @@ -1094,7 +1099,7 @@ 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; } @@ -1105,12 +1110,38 @@ 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 */ + sport = 0; + dport = 0; + + saddr = ntohl(pip->saddr); + daddr = ntohl(pip->daddr); + protocol = pip->protocol; + + /* whole packet? */ + if (BLEN(buf) == (ip_hdr_offset + (int)(ntohs(pip->tot_len)))) + { + const uint8_t *payload = BPTR(buf) + ip_hdr_offset + sizeof(struct openvpn_iphdr); + + 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 if (proto_ver == 6) @@ -1118,7 +1149,7 @@ 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; } @@ -1129,22 +1160,68 @@ 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 */ + sport = 0; + dport = 0; + + saddr6 = pip6->saddr; + daddr6 = pip6->daddr; + protocol = pip6->nexthdr; + + /* whole packet? */ + if (BLEN(buf) == ((int)sizeof(struct openvpn_ipv6hdr) + ip_hdr_offset + (int)ntohs(pip6->payload_len))) + { + const uint8_t *payload = BPTR(buf) + ip_hdr_offset + sizeof(struct openvpn_ipv6hdr); + + 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); + } + } } } 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, "%s", "UDP"); + else if (protocol == OPENVPN_IPPROTO_TCP) + buf_printf(&addrs_buf, "%s", "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); } }