passt: New design and implementation with native Layer 4 sockets

This is a reimplementation, partially building on the earlier draft,
that uses L4 sockets (SOCK_DGRAM, SOCK_STREAM) instead of SOCK_RAW,
providing L4-L2 translation functionality without requiring any
security capability.

Conceptually, this follows the design presented at:
	https://gitlab.com/abologna/kubevirt-and-kvm/-/blob/master/Networking.md

The most significant novelty here comes from TCP and UDP translation
layers. In particular, the TCP state and translation logic follows
the intent of being minimalistic, without reimplementing a full TCP
stack in either direction, and synchronising as much as possible the
TCP dynamic and flows between guest and host kernel.

Another important introduction concerns addressing, port translation
and forwarding. The Layer 4 implementations now attempt to bind on
all unbound ports, in order to forward connections in a transparent
way.

While at it:
- the qemu 'tap' back-end can't be used as-is by qrap anymore,
  because of explicit checks now introduced in qemu to ensure that
  the corresponding file descriptor is actually a tap device. For
  this reason, qrap now operates on a 'socket' back-end type,
  accounting for and building the additional header reporting
  frame length

- provide a demo script that sets up namespaces, addresses and
  routes, and starts the daemon. A virtual machine started in the
  network namespace, wrapped by qrap, will now directly interface
  with passt and communicate using Layer 4 sockets provided by the
  host kernel.

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

1 files changed, 138 insertions, 3 deletions

diff --git a/util.c b/util.c
index 7dd0db1..324f800 100644
--- a/util.c
+++ b/util.c
@@ -1,17 +1,28 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
 /* PASST - Plug A Simple Socket Transport
  *
  * util.c - Convenience helpers
  *
+ * Copyright (c) 2020-2021 Red Hat GmbH
  * Author: Stefano Brivio <sbrivio@redhat.com>
- * License: GPLv2
  *
  */
 
 #include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <unistd.h>
 #include <linux/ipv6.h>
 #include <arpa/inet.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+#include <netinet/udp.h>
+#include <sys/epoll.h>
+
+#include "passt.h"
 
 /**
  * csum_fold() - Fold long sum for IP and TCP checksum
@@ -50,7 +61,45 @@ uint16_t csum_ip4(void *buf, size_t len)
 	return ~csum_fold(sum);
 }
 
-unsigned char *ipv6_l4hdr(struct ipv6hdr *ip6h, uint8_t *proto)
+/**
+ * csum_ipv4() - Calculate TCP checksum for IPv4 and set in place
+ * @iph:	Packet buffer, IP header
+ */
+void csum_tcp4(struct iphdr *iph)
+{
+	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
+	uint16_t tlen = ntohs(iph->tot_len) - iph->ihl * 4, *p = (uint16_t *)th;
+	uint32_t sum = 0;
+
+	sum += (iph->saddr >> 16) & 0xffff;
+	sum += iph->saddr & 0xffff;
+	sum += (iph->daddr >> 16) & 0xffff;
+	sum += iph->daddr & 0xffff;
+
+	sum += htons(IPPROTO_TCP);
+	sum += htons(tlen);
+
+	th->check = 0;
+	while (tlen > 1) {
+		sum += *p++;
+		tlen -= 2;
+	}
+
+	if (tlen > 0) {
+		sum += *p & htons(0xff00);
+	}
+
+	th->check = (uint16_t)~csum_fold(sum);
+}
+
+/**
+ * ipv6_l4hdr() - Find pointer to L4 header in IPv6 packet and extract protocol
+ * @ip6h:	IPv6 header
+ * @proto:	Filled with L4 protocol number
+ *
+ * Return: pointer to L4 header, NULL if not found
+ */
+char *ipv6_l4hdr(struct ipv6hdr *ip6h, uint8_t *proto)
 {
 	int offset, len, hdrlen;
 	struct ipv6_opt_hdr *o;
@@ -79,9 +128,95 @@ unsigned char *ipv6_l4hdr(struct ipv6hdr *ip6h, uint8_t *proto)
 								    offset;
 		} else {
 			*proto = nh;
-			return (unsigned char *)(ip6h + 1) + offset;
+			return (char *)(ip6h + 1) + offset;
 		}
 	}
 
 	return NULL;
 }
+
+/**
+ * sock_l4_add() - Create and bind socket for given L4, add to epoll list
+ * @c:		Execution context
+ * @v:		IP protocol, 4 or 6
+ * @proto:	Protocol number, network order
+ * @port:	Port, network order
+ *
+ * Return: newly created socket, -1 on error
+ */
+int sock_l4_add(struct ctx *c, int v, uint16_t proto, uint16_t port)
+{
+	struct sockaddr_in addr4 = {
+		.sin_family = AF_INET,
+		.sin_port = port,
+		.sin_addr = { .s_addr = INADDR_ANY },
+	};
+	struct sockaddr_in6 addr6 = {
+		.sin6_family = AF_INET6,
+		.sin6_port = port,
+		.sin6_addr = IN6ADDR_ANY_INIT,
+	};
+	struct epoll_event ev = { 0 };
+	const struct sockaddr *sa;
+	int fd, sl;
+
+	if (proto != IPPROTO_TCP && proto != IPPROTO_UDP)
+		return -1;	/* Not implemented. */
+
+	fd = socket(v == 4 ? AF_INET : AF_INET6,
+		    proto == IPPROTO_TCP ? SOCK_STREAM : SOCK_DGRAM, proto);
+	if (fd < 0) {
+		perror("L4 socket");
+		return -1;
+	}
+
+	if (v == 4) {
+		sa = (const struct sockaddr *)&addr4;
+		sl = sizeof(addr4);
+	} else {
+		sa = (const struct sockaddr *)&addr6;
+		sl = sizeof(addr6);
+	}
+
+	if (bind(fd, sa, sl) < 0) {
+		/* We'll fail to bind to low ports if we don't have enough
+		 * capabilities, and we'll fail to bind on already bound ports,
+		 * this is fine.
+		 */
+		close(fd);
+		return 0;
+	}
+
+	if (proto == IPPROTO_TCP && listen(fd, 128) < 0) {
+		perror("TCP socket listen");
+		close(fd);
+		return -1;
+	}
+
+	ev.events = EPOLLIN;
+	ev.data.fd = fd;
+	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
+		perror("L4 epoll_ctl");
+		return -1;
+	}
+
+	return fd;
+}
+
+/**
+ * timespec_diff_ms() - Report difference in milliseconds between two timestamps
+ * @a:		Minuend timestamp
+ * @b:		Subtrahend timestamp
+ *
+ * Return: difference in milliseconds
+ */
+int timespec_diff_ms(struct timespec *a, struct timespec *b)
+{
+	if (a->tv_nsec < b->tv_nsec) {
+		return (b->tv_nsec - a->tv_nsec) / 1000 +
+		       (a->tv_sec - b->tv_sec - 1) * 1000;
+	}
+
+	return (a->tv_nsec - b->tv_nsec) / 1000 +
+	       (a->tv_sec - b->tv_sec) * 1000;
+}