1 files changed, 140 insertions, 0 deletions
diff --git a/srclimit.c b/srclimit.c
new file mode 100644
index 0000000..5014ed7
--- /dev/null
+++ b/srclimit.c
@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2020 Darren Tucker <dtucker@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "includes.h"
+
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <limits.h>
+#include <netdb.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "addr.h"
+#include "canohost.h"
+#include "log.h"
+#include "misc.h"
+#include "srclimit.h"
+#include "xmalloc.h"
+
+static int max_children, max_persource, ipv4_masklen, ipv6_masklen;
+
+/* Per connection state, used to enforce unauthenticated connection limit. */
+static struct child_info {
+	int id;
+	struct xaddr addr;
+} *child;
+
+void
+srclimit_init(int max, int persource, int ipv4len, int ipv6len)
+{
+	int i;
+
+	max_children = max;
+	ipv4_masklen = ipv4len;
+	ipv6_masklen = ipv6len;
+	max_persource = persource;
+	if (max_persource == INT_MAX)	/* no limit */
+		return;
+	debug("%s: max connections %d, per source %d, masks %d,%d", __func__,
+	    max, persource, ipv4len, ipv6len);
+	if (max <= 0)
+		fatal("%s: invalid number of sockets: %d", __func__, max);
+	child = xcalloc(max_children, sizeof(*child));
+	for (i = 0; i < max_children; i++)
+		child[i].id = -1;
+}
+
+/* returns 1 if connection allowed, 0 if not allowed. */
+int
+srclimit_check_allow(int sock, int id)
+{
+	struct xaddr xa, xb, xmask;
+	struct sockaddr_storage addr;
+	socklen_t addrlen = sizeof(addr);
+	struct sockaddr *sa = (struct sockaddr *)&addr;
+	int i, bits, first_unused, count = 0;
+	char xas[NI_MAXHOST];
+
+	if (max_persource == INT_MAX)	/* no limit */
+		return 1;
+
+	debug("%s: sock %d id %d limit %d", __func__, sock, id, max_persource);
+	if (getpeername(sock, sa, &addrlen) != 0)
+		return 1;	/* not remote socket? */
+	if (addr_sa_to_xaddr(sa, addrlen, &xa) != 0)
+		return 1;	/* unknown address family? */
+
+	/* Mask address off address to desired size. */
+	bits = xa.af == AF_INET ? ipv4_masklen : ipv6_masklen;
+	if (addr_netmask(xa.af, bits, &xmask) != 0 ||
+	    addr_and(&xb, &xa, &xmask) != 0) {
+		debug3("%s: invalid mask %d bits", __func__, bits);
+		return 1;
+	}
+
+	first_unused = max_children;
+	/* Count matching entries and find first unused one. */
+	for (i = 0; i < max_children; i++) {
+		if (child[i].id == -1) {
+			if (i < first_unused)
+				first_unused = i;
+		} else if (addr_cmp(&child[i].addr, &xb) == 0) {
+			count++;
+		}
+	}
+	if (addr_ntop(&xa, xas, sizeof(xas)) != 0) {
+		debug3("%s: addr ntop failed", __func__);
+		return 1;
+	}
+	debug3("%s: new unauthenticated connection from %s/%d, at %d of %d",
+	    __func__, xas, bits, count, max_persource);
+
+	if (first_unused == max_children) { /* no free slot found */
+		debug3("%s: no free slot", __func__);
+		return 0;
+	}
+	if (first_unused < 0 || first_unused >= max_children)
+		fatal("%s: internal error: first_unused out of range",
+		    __func__);
+
+	if (count >= max_persource)
+		return 0;
+
+	/* Connection allowed, store masked address. */
+	child[first_unused].id = id;
+	memcpy(&child[first_unused].addr, &xb, sizeof(xb));
+	return 1;
+}
+
+void
+srclimit_done(int id)
+{
+	int i;
+
+	if (max_persource == INT_MAX)	/* no limit */
+		return;
+
+	debug("%s: id %d", __func__, id);
+	/* Clear corresponding state entry. */
+	for (i = 0; i < max_children; i++) {
+		if (child[i].id == id) {
+			child[i].id = -1;
+			return;
+		}
+	}
+}