tcp: Add siphash implementation for initial sequence numbers

Implement siphash routines for initial TCP sequence numbers (12 bytes
input for IPv4, 36 bytes input for IPv6), and while at it, also
functions we'll use later on for hash table indices and TCP timestamp
offsets (with 8, 20, 32 bytes of input).

Use these to set the initial sequence number, according to RFC 6528,
for connections originating either from the tap device or from
sockets.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Makefile

@@ -2,8 +2,8 @@ CFLAGS += -Wall -Wextra -pedantic
 
 all: passt qrap
 
-passt: passt.c passt.h arp.c arp.h dhcp.c dhcp.h ndp.c ndp.h tap.c tap.h tcp.c tcp.h udp.c udp.h util.c util.h
+passt: passt.c passt.h arp.c arp.h dhcp.c dhcp.h ndp.c ndp.h siphash.c siphash.h tap.c tap.h tcp.c tcp.h udp.c udp.h util.c util.h
-	$(CC) $(CFLAGS) passt.c arp.c dhcp.c ndp.c tap.c tcp.c udp.c util.c -o passt
+	$(CC) $(CFLAGS) passt.c arp.c dhcp.c ndp.c siphash.c tap.c tcp.c udp.c util.c -o passt
 
 qrap: qrap.c passt.h
 	$(CC) $(CFLAGS) qrap.c -o qrap

siphash.c

@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *
+ * siphash.c - SipHash routines
+ *
+ * Copyright (c) 2020-2021 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ *
+ * This is an implementation of the SipHash-2-4-64 functions needed for TCP
+ * initial sequence numbers and socket lookup table hash for IPv4 and IPv6, see:
+ *
+ *	Aumasson, J.P. and Bernstein, D.J., 2012, December. SipHash: a fast
+ *	short-input PRF. In International Conference on Cryptology in India
+ *	(pp. 489-508). Springer, Berlin, Heidelberg.
+ *
+ *	http://cr.yp.to/siphash/siphash-20120918.pdf
+ *
+ * This includes code from the reference SipHash implementation at
+ * https://github.com/veorq/SipHash/ licensed as follows:
+ *
+ * --
+ *  SipHash reference C implementation
+ *
+ * Copyright (c) 2012-2021 Jean-Philippe Aumasson
+ * <jeanphilippe.aumasson@gmail.com>
+ * Copyright (c) 2012-2014 Daniel J. Bernstein <djb@cr.yp.to>
+ *
+ * To the extent possible under law, the author(s) have dedicated all copyright
+ * and related and neighboring rights to this software to the public domain
+ * worldwide. This software is distributed without any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication along
+ * with
+ * this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ * --
+ *
+ * and from the Linux kernel implementation (lib/siphash.c), licensed as
+ * follows:
+ *
+ * --
+ * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ * --
+ *
+ */
+
+#include <stdint.h>
+
+#include "siphash.h"
+
+#define ROTL(x, b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))
+
+#define PREAMBLE(len)							  \
+	uint64_t v[4] = { 0x736f6d6570736575ULL, 0x646f72616e646f6dULL,	  \
+			  0x6c7967656e657261ULL, 0x7465646279746573ULL }; \
+	uint64_t b = (uint64_t)(len) << 56;				  \
+	uint32_t ret;							  \
+	int __i;							  \
+									  \
+	do {								  \
+		for (__i = sizeof(v) / sizeof(v[0]); __i >= 0; __i--)	  \
+			v[__i] = k[__i % 2];				  \
+	} while (0)
+
+#define SIPROUND(n)							  \
+	do {								  \
+		for (__i = 0; __i < (n); __i++) {			  \
+			v[0] += v[1];					  \
+			v[1] = ROTL(v[1], 13) ^ v[0];			  \
+			v[0] = ROTL(v[0], 32);				  \
+			v[2] += v[3];					  \
+			v[3] = ROTL(v[3], 16) ^ v[2];			  \
+			v[0] += v[3];					  \
+			v[3] = ROTL(v[3], 21) ^ v[0];			  \
+			v[2] += v[1];					  \
+			v[1] = ROTL(v[1], 17) ^ v[2];			  \
+			v[2] = ROTL(v[2], 32);				  \
+		}							  \
+	} while (0)
+
+#define POSTAMBLE							  \
+	do {								  \
+		v[3] ^= b;						  \
+		SIPROUND(2);						  \
+		v[0] ^= b;						  \
+		v[2] ^= 0xff;						  \
+		SIPROUND(4);						  \
+		b = (v[0] ^ v[1]) ^ (v[2] ^ v[3]);			  \
+		ret = (uint32_t)(b >> 32) ^ (uint32_t)b;		  \
+		(void)ret;						  \
+	} while (0)
+
+/**
+ * siphash_8b() - Table index or timestamp offset for TCP over IPv4 (8 bytes in)
+ * @in:		Input data (remote address and two ports, or two addresses)
+ * @k:		Hash function key, 128 bits
+ *
+ * Return: the 64-bit hash output
+ */
+uint64_t siphash_8b(const uint8_t *in, const uint64_t *k)
+{
+	PREAMBLE(8);
+	v[3] ^= *(uint64_t *)in;
+	SIPROUND(2);
+	v[0] ^= *(uint64_t *)in;
+	POSTAMBLE;
+
+	return b;
+}
+
+/**
+ * siphash_12b() - Initial sequence number for TCP over IPv4 (12 bytes in)
+ * @in:		Input data (two addresses, two ports)
+ * @k:		Hash function key, 128 bits
+ *
+ * Return: 32 bits obtained by XORing the two halves of the 64-bit hash output
+ */
+uint32_t siphash_12b(const uint8_t *in, const uint64_t *k)
+{
+	uint32_t *in32 = (uint32_t *)in;
+	uint64_t combined;
+
+	combined = (uint64_t)(*(in32 + 1)) << 32 | *in32;
+
+	PREAMBLE(12);
+	v[3] ^= combined;
+	SIPROUND(2);
+	v[0] ^= combined;
+	b |= *(in32 + 2);
+	POSTAMBLE;
+
+	return ret;
+}
+
+/**
+ * siphash_20b() - Table index for TCP over IPv6 (20 bytes in)
+ * @in:		Input data (remote address, two ports)
+ * @k:		Hash function key, 128 bits
+ *
+ * Return: the 64-bit hash output
+ */
+uint64_t siphash_20b(const uint8_t *in, const uint64_t *k)
+{
+	uint32_t *in32 = (uint32_t *)in;
+	uint64_t combined;
+	int i;
+
+	PREAMBLE(20);
+
+	for (i = 0; i < 2; i++, in32 += 2) {
+		combined = (uint64_t)(*(in32 + 1)) << 32 | *in32;
+		v[3] ^= combined;
+		SIPROUND(2);
+		v[0] ^= combined;
+	}
+
+	b |= *in32;
+	POSTAMBLE;
+
+	return b;
+}
+
+/**
+ * siphash_32b() - Timestamp offset for TCP over IPv6 (32 bytes in)
+ * @in:		Input data (two addresses)
+ * @k:		Hash function key, 128 bits
+ *
+ * Return: the 64-bit hash output
+ */
+uint32_t siphash_32b(const uint8_t *in, const uint64_t *k)
+{
+	uint64_t *in64 = (uint64_t *)in;
+	int i;
+
+	PREAMBLE(32);
+
+	for (i = 0; i < 4; i++, in64++) {
+		v[3] ^= *in64;
+		SIPROUND(2);
+		v[0] ^= *in64;
+	}
+
+	POSTAMBLE;
+
+	return b;
+}
+
+/**
+ * siphash_36b() - Initial sequence number for TCP over IPv6 (36 bytes in)
+ * @in:		Input data (two addresses, two ports)
+ * @k:		Hash function key, 128 bits
+ *
+ * Return: 32 bits obtained by XORing the two halves of the 64-bit hash output
+ */
+uint32_t siphash_36b(const uint8_t *in, const uint64_t *k)
+{
+	uint32_t *in32 = (uint32_t *)in;
+	uint64_t combined;
+	int i;
+
+	PREAMBLE(36);
+
+	for (i = 0; i < 4; i++, in32 += 2) {
+		combined = (uint64_t)(*(in32 + 1)) << 32 | *in32;
+		v[3] ^= combined;
+		SIPROUND(2);
+		v[0] ^= combined;
+	}
+
+	b |= *in32;
+	POSTAMBLE;
+
+	return ret;
+}

siphash.h

@@ -0,0 +1,5 @@
+uint64_t siphash_8b(const uint8_t *in, const uint64_t *k);
+uint32_t siphash_12b(const uint8_t *in, const uint64_t *k);
+uint64_t siphash_20b(const uint8_t *in, const uint64_t *k);
+uint32_t siphash_32b(const uint8_t *in, const uint64_t *k);
+uint32_t siphash_36b(const uint8_t *in, const uint64_t *k);

tcp.c

@@ -304,8 +304,9 @@
 #include <stddef.h>
 #include <string.h>
 #include <sys/epoll.h>
-#include <sys/types.h>
+#include <sys/random.h>
 #include <sys/socket.h>
+#include <sys/types.h>
 #include <unistd.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
@@ -315,6 +316,7 @@
 #include "passt.h"
 #include "tap.h"
 #include "util.h"
+#include "siphash.h"
 
 /* Approximately maximum number of open descriptors per process */
 #define MAX_CONNS			(256 * 1024)
@@ -430,6 +432,7 @@ struct tcp_conn {
 static char sock_buf[MAX_WINDOW];
 static uint8_t tcp_act[MAX_CONNS / 8] = { 0 };
 static struct tcp_conn tc[MAX_CONNS];
+static uint64_t hash_secret[2];
 
 static int tcp_send_to_tap(struct ctx *c, int s, int flags, char *in, int len);
 
@@ -676,6 +679,60 @@ static void tcp_clamp_window(int s, struct tcphdr *th, int len, int init)
 	}
 }
 
+/**
+ * tcp_seq_init() - Calculate initial sequence number according to RFC 6528
+ * @c:		Execution context
+ * @af:		Address family, AF_INET or AF_INET6
+ * @addr:	Remote address, pointer to sin_addr or sin6_addr
+ * @dstport:	Destination port, connection-wise, network order
+ * @srcport:	Source port, connection-wise, network order
+ *
+ * Return: initial TCP sequence
+ */
+static uint32_t tcp_seq_init(struct ctx *c, int af, void *addr,
+			     in_port_t dstport, in_port_t srcport)
+{
+	struct timespec ts = { 0 };
+	uint32_t ns, seq;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+
+	if (af == AF_INET) {
+		struct {
+			struct in_addr src;
+			in_port_t srcport;
+			struct in_addr dst;
+			in_port_t dstport;
+		} __attribute__((__packed__)) in = {
+			.src = *(struct in_addr *)addr,
+			.srcport = srcport,
+			.dst = *(struct in_addr *)c->addr4,
+			.dstport = dstport,
+		};
+
+		seq = siphash_12b((uint8_t *)&in, hash_secret);
+	} else if (af == AF_INET6) {
+		struct {
+			struct in6_addr src;
+			in_port_t srcport;
+			struct in6_addr dst;
+			in_port_t dstport;
+		} __attribute__((__packed__)) in = {
+			.src = *(struct in6_addr *)addr,
+			.srcport = srcport,
+			.dst = c->addr6,
+			.dstport = dstport,
+		};
+
+		seq = siphash_36b((uint8_t *)&in, hash_secret);
+	}
+
+	ns = ts.tv_sec * 1E9;
+	ns += ts.tv_nsec >> 5;	/* 32ns ticks, overflows 32 bits every 137s */
+
+	return seq + ns;
+}
+
 /**
  * tcp_conn_from_tap() - Handle connection request (SYN segment) from tap
  * @c:		Execution context
@@ -744,9 +801,8 @@ static void tcp_conn_from_tap(struct ctx *c, int af, void *addr,
 	tc[s].seq_from_tap = tc[s].seq_init_from_tap + 1;
 	tc[s].seq_ack_to_tap = tc[s].seq_from_tap;
 
-	/* TODO: RFC 6528 with SipHash, worth it? */
+	tc[s].seq_to_tap = tcp_seq_init(c, af, addr, th->dest, th->source);
-	tc[s].seq_to_tap = 0;
+	tc[s].seq_ack_from_tap = tc[s].seq_to_tap + 1;
-	tc[s].seq_ack_from_tap = tc[s].seq_to_tap;
 
 	if (connect(s, sa, sl)) {
 		if (errno != EINPROGRESS) {
@@ -827,6 +883,10 @@ static void tcp_conn_from_sock(struct ctx *c, int fd)
 
 		tc[s].sock_port = sa4->sin_port;
 		tc[s].tap_port = ((struct sockaddr_in *)&sa_l)->sin_port;
+
+		tc[s].seq_to_tap = tcp_seq_init(c, AF_INET, &sa4->sin_addr,
+						tc[s].sock_port,
+						tc[s].tap_port);
 	} else if (sa_l.ss_family == AF_INET6) {
 		struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)&sa_r;
 
@@ -834,10 +894,12 @@ static void tcp_conn_from_sock(struct ctx *c, int fd)
 
 		tc[s].sock_port = sa6->sin6_port;
 		tc[s].tap_port = ((struct sockaddr_in6 *)&sa_l)->sin6_port;
+
+		tc[s].seq_to_tap = tcp_seq_init(c, AF_INET6, &sa6->sin6_addr,
+						tc[s].sock_port,
+						tc[s].tap_port);
 	}
 
-	/* TODO: RFC 6528 with SipHash, worth it? */
-	tc[s].seq_to_tap = 0;
 	tc[s].seq_ack_from_tap = tc[s].seq_to_tap + 1;
 
 	tc[s].tap_window = WINDOW_DEFAULT;
@@ -1230,7 +1292,7 @@ void tcp_sock_handler(struct ctx *c, int s, uint32_t events)
 }
 
 /**
- * tcp_sock_init() - Create and bind listening sockets for inbound connections
+ * tcp_sock_init() - Bind sockets for inbound connections, get key for sequence
  * @c:		Execution context
  *
  * Return: 0 on success, -1 on failure
@@ -1246,6 +1308,8 @@ int tcp_sock_init(struct ctx *c)
 			return -1;
 	}
 
+	getrandom(hash_secret, sizeof(hash_secret), GRND_RANDOM);
+
 	return 0;
 }