Initial import of RFC 2385 (TCP-MD5) digest support.

This is the first of two commits; bringing in the kernel support first.
This can be enabled by compiling a kernel with options TCP_SIGNATURE
and FAST_IPSEC.

For the uninitiated, this is a TCP option which provides for a means of
authenticating TCP sessions which came into being before IPSEC. It is
still relevant today, however, as it is used by many commercial router
vendors, particularly with BGP, and as such has become a requirement for
interconnect at many major Internet points of presence.

Several parts of the TCP and IP headers, including the segment payload,
are digested with MD5, including a shared secret. The PF_KEY interface
is used to manage the secrets using security associations in the SADB.

There is a limitation here in that as there is no way to map a TCP flow
per-port back to an SPI without polluting tcpcb or using the SPD; the
code to do the latter is unstable at this time. Therefore this code only
supports per-host keying granularity.

Whilst FAST_IPSEC is mutually exclusive with KAME IPSEC (and thus IPv6),
TCP_SIGNATURE applies only to IPv4. For the vast majority of prospective
users of this feature, this will not pose any problem.

This implementation is output-only; that is, the option is honoured when
responding to a host initiating a TCP session, but no effort is made
[yet] to authenticate inbound traffic. This is, however, sufficient to
interwork with Cisco equipment.

Tested with a Cisco 2501 running IOS 12.0(27), and Quagga 0.96.4 with
local patches. Patches for tcpdump to validate TCP-MD5 sessions are also
available from me upon request.

Sponsored by:	sentex.net

1 files changed, 25 insertions, 0 deletions

diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index 33353b4..0390f1e 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -105,6 +105,7 @@ struct tcpcb {
 #define	TF_RXWIN0SENT	0x080000	/* sent a receiver win 0 in response */
 #define	TF_FASTRECOVERY	0x100000	/* in NewReno Fast Recovery */
 #define	TF_WASFRECOVERY	0x200000	/* was in NewReno Fast Recovery */
+#define	TF_SIGNATURE	0x400000	/* require MD5 digests (RFC2385) */
 	int	t_force;		/* 1 if forcing out a byte */
 
 	tcp_seq	snd_una;		/* send unacknowledged */
@@ -189,6 +190,21 @@ struct tcpcb {
 #define ENTER_FASTRECOVERY(tp)	tp->t_flags |= TF_FASTRECOVERY
 #define EXIT_FASTRECOVERY(tp)	tp->t_flags &= ~TF_FASTRECOVERY
 
+#ifdef TCP_SIGNATURE
+/*
+ * Defines which are needed by the xform_tcp module and tcp_[in|out]put
+ * for SADB verification and lookup.
+ */
+#define	TCP_SIGLEN	16	/* length of computed digest in bytes */
+#define	TCP_KEYLEN_MIN	1	/* minimum length of TCP-MD5 key */
+#define	TCP_KEYLEN_MAX	80	/* maximum length of TCP-MD5 key */
+/*
+ * Only a single SA per host may be specified at this time. An SPI is
+ * needed in order for the KEY_ALLOCSA() lookup to work.
+ */
+#define	TCP_SIG_SPI	0x1000
+#endif /* TCP_SIGNATURE */
+
 /*
  * Structure to hold TCP options that are only used during segment
  * processing (in tcp_input), but not held in the tcpcb.
@@ -203,6 +219,8 @@ struct tcpopt {
 #define	TOF_CCECHO	0x0008
 #define	TOF_MSS		0x0010
 #define	TOF_SCALE	0x0020
+#define	TOF_SIGNATURE	0x0040		/* signature option present */
+#define	TOF_SIGLEN	0x0080		/* sigature length valid (RFC2385) */
 	u_int32_t	to_tsval;
 	u_int32_t	to_tsecr;
 	tcp_cc		to_cc;		/* holds CC or CCnew */
@@ -234,6 +252,7 @@ struct syncache {
 #define SCF_TIMESTAMP	0x04			/* negotiated timestamps */
 #define SCF_CC		0x08			/* negotiated CC */
 #define SCF_UNREACH	0x10			/* icmp unreachable received */
+#define SCF_SIGNATURE	0x20			/* send MD5 digests */
 	TAILQ_ENTRY(syncache)	sc_hash;
 	TAILQ_ENTRY(syncache)	sc_timerq;
 };
@@ -549,6 +568,12 @@ void	 tcp_hc_updatetao(struct in_conninfo *, int, tcp_cc, u_short);
 #define TCP_HC_TAO_CCSENT	0x2
 #define TCP_HC_TAO_MSSOPT	0x3
 
+#ifdef TCP_SIGNATURE
+int tcpsignature_apply(void *fstate, void *data, unsigned int len);
+int tcpsignature_compute(struct mbuf *m, int off0, int len, int tcpoptlen,
+    u_char *buf, u_int direction);
+#endif /* TCP_SIGNATURE */
+
 extern	struct pr_usrreqs tcp_usrreqs;
 extern	u_long tcp_sendspace;
 extern	u_long tcp_recvspace;