contrib: add sticky sockets example code

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

contrib/sticky-sockets/README

@@ -0,0 +1,5 @@
+Sticky Sockets
+==============
+
+This is a small userspace mini-library that implements as close to
+possible how the kernel does its sticky src address sending.

contrib/sticky-sockets/sticky-sockets.c

@@ -0,0 +1,337 @@
+/* Copyright 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This implements userspace semantics of "sticky sockets", modeled after
+ * WireGuard's kernelspace implementation.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <linux/ipv6.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/udp.h>
+#include <arpa/inet.h>
+
+struct magic_endpoint {
+	union {
+		struct sockaddr addr;
+		struct sockaddr_in addr4;
+		struct sockaddr_in6 addr6;
+	};
+	union {
+		struct {
+			struct in_addr src4;
+			int src_if4; /* Essentially the same as addr6->scope_id */
+		};
+		struct in6_addr src6;
+	};
+};
+
+ssize_t magic_send4(int sock, struct magic_endpoint *endpoint, void *buffer, size_t len)
+{
+	ssize_t ret;
+	struct iovec iovec = {
+		.iov_base = buffer,
+		.iov_len = len
+	};
+	struct {
+		struct cmsghdr cmsghdr;
+		struct in_pktinfo pktinfo;
+	} cmsg = {
+		.cmsghdr.cmsg_level = IPPROTO_IP,
+		.cmsghdr.cmsg_type = IP_PKTINFO,
+		.cmsghdr.cmsg_len = CMSG_LEN(sizeof(cmsg.pktinfo)),
+		.pktinfo.ipi_spec_dst = endpoint->src4,
+		.pktinfo.ipi_ifindex = endpoint->src_if4
+	};
+	struct msghdr msghdr = {
+		.msg_iov = &iovec,
+		.msg_iovlen = 1,
+		.msg_name = &endpoint->addr4,
+		.msg_namelen = sizeof(endpoint->addr4),
+		.msg_control = &cmsg,
+		.msg_controllen = sizeof(cmsg)
+	};
+	ret = sendmsg(sock, &msghdr, 0);
+	if (ret < 0 && errno == EINVAL) {
+		memset(&cmsg.pktinfo, 0, sizeof(cmsg.pktinfo));
+		endpoint->src4.s_addr = endpoint->src_if4 = 0;
+		return sendmsg(sock, &msghdr, 0);
+	}
+	return ret;
+}
+
+ssize_t magic_send6(int sock, struct magic_endpoint *endpoint, void *buffer, size_t len)
+{
+	ssize_t ret;
+	struct iovec iovec = {
+		.iov_base = buffer,
+		.iov_len = len
+	};
+	struct {
+		struct cmsghdr cmsghdr;
+		struct in6_pktinfo pktinfo;
+	} cmsg = {
+		.cmsghdr.cmsg_level = IPPROTO_IPV6,
+		.cmsghdr.cmsg_type = IPV6_PKTINFO,
+		.cmsghdr.cmsg_len = CMSG_LEN(sizeof(cmsg.pktinfo)),
+		.pktinfo.ipi6_addr = endpoint->src6,
+		.pktinfo.ipi6_ifindex = memcmp(&in6addr_any, &endpoint->src6, sizeof(endpoint->src6)) ? endpoint->addr6.sin6_scope_id : 0
+	};
+	struct msghdr msghdr = {
+		.msg_iov = &iovec,
+		.msg_iovlen = 1,
+		.msg_name = &endpoint->addr6,
+		.msg_namelen = sizeof(endpoint->addr6),
+		.msg_control = &cmsg,
+		.msg_controllen = sizeof(cmsg)
+	};
+
+	ret = sendmsg(sock, &msghdr, 0);
+	if (ret < 0 && errno == EINVAL) {
+		memset(&cmsg.pktinfo, 0, sizeof(cmsg.pktinfo));
+		memset(&endpoint->src6, 0, sizeof(endpoint->src6));
+		return sendmsg(sock, &msghdr, 0);
+	}
+	return ret;
+}
+
+ssize_t magic_receive4(int sock, struct magic_endpoint *endpoint, void *buffer, size_t len)
+{
+	ssize_t ret;
+	struct iovec iovec = {
+		.iov_base = buffer,
+		.iov_len = len
+	};
+	struct {
+		struct cmsghdr cmsghdr;
+		struct in_pktinfo pktinfo;
+	} cmsg;
+	struct msghdr msghdr = {
+		.msg_iov = &iovec,
+		.msg_iovlen = 1,
+		.msg_name = &endpoint->addr4,
+		.msg_namelen = sizeof(endpoint->addr4),
+		.msg_control = &cmsg,
+		.msg_controllen = sizeof(cmsg)
+	};
+
+	ret = recvmsg(sock, &msghdr, 0);
+	if (ret < 0)
+		return ret;
+	if (cmsg.cmsghdr.cmsg_level == IPPROTO_IP && cmsg.cmsghdr.cmsg_type == IP_PKTINFO && cmsg.cmsghdr.cmsg_len >= CMSG_LEN(sizeof(cmsg.pktinfo))) {
+		endpoint->src4 = cmsg.pktinfo.ipi_spec_dst;
+		endpoint->src_if4 = cmsg.pktinfo.ipi_ifindex;
+	}
+	return ret;
+}
+
+ssize_t magic_receive6(int sock, struct magic_endpoint *endpoint, void *buffer, size_t len)
+{
+	ssize_t ret;
+	struct iovec iovec = {
+		.iov_base = buffer,
+		.iov_len = len
+	};
+	struct {
+		struct cmsghdr cmsghdr;
+		struct in6_pktinfo pktinfo;
+	} cmsg;
+	struct msghdr msghdr = {
+		.msg_iov = &iovec,
+		.msg_iovlen = 1,
+		.msg_name = &endpoint->addr6,
+		.msg_namelen = sizeof(endpoint->addr6),
+		.msg_control = &cmsg,
+		.msg_controllen = sizeof(cmsg)
+	};
+
+	ret = recvmsg(sock, &msghdr, 0);
+	if (ret < 0)
+		return ret;
+	if (cmsg.cmsghdr.cmsg_level == IPPROTO_IPV6 && cmsg.cmsghdr.cmsg_type == IPV6_PKTINFO && cmsg.cmsghdr.cmsg_len >= CMSG_LEN(sizeof(cmsg.pktinfo))) {
+		endpoint->src6 = cmsg.pktinfo.ipi6_addr;
+		endpoint->addr6.sin6_scope_id = cmsg.pktinfo.ipi6_ifindex;
+	}
+	return ret;
+}
+
+void magic_endpoint_clearsrc(struct magic_endpoint *endpoint)
+{
+	if (endpoint->addr.sa_family == AF_INET)
+		endpoint->src4.s_addr = endpoint->src_if4 = 0;
+	else if (endpoint->addr.sa_family == AF_INET6)
+		memset(&endpoint->src6, 0, sizeof(endpoint->src6));
+	else
+		memset(endpoint, 0, sizeof(*endpoint));
+}
+
+void magic_endpoint_set(struct magic_endpoint *endpoint, const struct sockaddr *addr)
+{
+	if (addr->sa_family == AF_INET)
+		endpoint->addr4 = *(struct sockaddr_in *)addr;
+	else if (addr->sa_family == AF_INET6)
+		endpoint->addr6 = *(struct sockaddr_in6 *)addr;
+	magic_endpoint_clearsrc(endpoint);
+}
+
+int magic_create_sock4(uint16_t listen_port)
+{
+	static const int on = 1;
+	struct sockaddr_in listen_addr = {
+		.sin_family = AF_INET,
+		.sin_port = htons(listen_port),
+		.sin_addr = INADDR_ANY
+	};
+	int fd, ret;
+	
+	fd = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd < 0)
+		return fd;
+	
+	ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
+	if (ret < 0)
+		goto err;
+	
+	ret = setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &on, sizeof(on));
+	if (ret < 0)
+		goto err;
+	
+	ret = bind(fd, (struct sockaddr *)&listen_addr, sizeof(listen_addr));
+	if (ret < 0)
+		goto err;
+	
+	return fd;
+
+err:
+	close(fd);
+	return ret;
+}
+
+int magic_create_sock6(uint16_t listen_port)
+{
+	static const int on = 1;
+	struct sockaddr_in6 listen_addr = {
+		.sin6_family = AF_INET6,
+		.sin6_port = htons(listen_port),
+		.sin6_addr = IN6ADDR_ANY_INIT
+	};
+	int fd, ret;
+	
+	fd = socket(AF_INET6, SOCK_DGRAM, 0);
+	if (fd < 0)
+		return fd;
+	
+	ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
+	if (ret < 0)
+		goto err;
+	
+	ret = setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &on, sizeof(on));
+	if (ret < 0)
+		goto err;
+
+	ret = setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on));
+	if (ret < 0)
+		goto err;
+	
+	ret = bind(fd, (struct sockaddr *)&listen_addr, sizeof(listen_addr));
+	if (ret < 0)
+		goto err;
+	
+	return fd;
+
+err:
+	close(fd);
+	return ret;
+}
+
+int main(int argc, char *argv[])
+{
+	struct magic_endpoint endpoint = { 0 };
+	int sock;
+	ssize_t ret;
+	uint8_t buffer[1024] = { 0 };
+	char srcaddr[40], dstaddr[40];
+
+	if (argc == 2 && !strcmp(argv[1], "-4"))
+		goto v4;
+	if (argc == 2 && !strcmp(argv[1], "-6"))
+		goto v6;
+	return 1;
+
+v6:
+	sock = magic_create_sock6(51820);
+	if (sock < 0) {
+		perror("magic_create_sock6");
+		return 1;
+	}
+
+	ret = magic_receive6(sock, &endpoint, buffer, sizeof(buffer));
+	if (ret < 0) {
+		perror("magic_receive6");
+		return 1;
+	}
+
+	if (!inet_ntop(AF_INET6, &endpoint.src6, srcaddr, sizeof(srcaddr))) {
+		perror("inet_ntop");
+		return 1;
+	}
+
+	if (!inet_ntop(AF_INET6, &endpoint.addr6.sin6_addr, dstaddr, sizeof(dstaddr))) {
+		perror("inet_ntop");
+		return 1;
+	}
+
+	printf("if:%d src:%s dst:%s\n", endpoint.addr6.sin6_scope_id, srcaddr, dstaddr);
+	printf("Received a packet. Sleeping for 10 seconds before replying, so you have time to mess with your networking setup.\n");
+	sleep(10);
+
+	ret = magic_send6(sock, &endpoint, buffer, sizeof(buffer));
+	if (ret < 0) {
+		perror("magic_send6");
+		return 1;
+	}
+
+	close(sock);
+	return 0;
+
+v4:
+	sock = magic_create_sock4(51820);
+	if (sock < 0) {
+		perror("magic_create_sock4");
+		return 1;
+	}
+
+	ret = magic_receive4(sock, &endpoint, buffer, sizeof(buffer));
+	if (ret < 0) {
+		perror("magic_receive4");
+		return 1;
+	}
+
+	if (!inet_ntop(AF_INET, &endpoint.src4, srcaddr, sizeof(srcaddr))) {
+		perror("inet_ntop");
+		return 1;
+	}
+
+	if (!inet_ntop(AF_INET, &endpoint.addr4.sin_addr, dstaddr, sizeof(dstaddr))) {
+		perror("inet_ntop");
+		return 1;
+	}
+
+	printf("if:%d src:%s dst:%s\n", endpoint.src_if4, srcaddr, dstaddr);
+	printf("Received a packet. Sleeping for 10 seconds before replying, so you have time to mess with your networking setup.\n");
+	sleep(10);
+
+	ret = magic_send4(sock, &endpoint, buffer, sizeof(buffer));
+	if (ret < 0) {
+		perror("magic_send4");
+		return 1;
+	}
+	
+	close(sock);
+	return 0;
+}