tools: pdivert — userspace relay for in-module AF_DIVERT family (M4 pending e2e)

tools/pdivert/pdivert.c

@@ -0,0 +1,107 @@
+/*
+ * pdivert — PF-on-Linux divert(4) relay (ISC 2026)
+ *
+ * Mirrors the classic BSD divert(8) workflow against the in-module
+ * PF_DIVERT socket family:
+ *
+ *	pdivert -p <port> [-f] [-q]
+ *	  -p port   bind the divert socket to <port> (matches pf rule port)
+ *	  -f        flip the last ICMP payload byte (demo rewrite)
+ *	  -q        quiet (no hexdump)
+ *
+ * Packets pulled from the socket are sent straight back (optionally
+ * mutated), reproducing "receive -> rewrite -> reinject".
+ *
+ * The kernel side (module/pfsrc/divert_sock.c) re-injects per OpenBSD
+ * ip_divert.c semantics using the metadata captured at divert time.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#ifndef PF_DIVERT
+#define PF_DIVERT	32	/* BSD PF_DIVERT; in-module family */
+#endif
+#ifndef IPPROTO_DIVERT
+#define IPPROTO_DIVERT	254
+#endif
+
+int
+main(int argc, char **argv)
+{
+	int fd, ch, port = 0, flip = 0, quiet = 0;
+	unsigned char buf[65536];
+
+	while ((ch = getopt(argc, argv, "p:fq")) != -1) {
+		switch (ch) {
+		case 'p':
+			port = atoi(optarg);
+			break;
+		case 'f':
+			flip = 1;
+			break;
+		case 'q':
+			quiet = 1;
+			break;
+		default:
+			fprintf(stderr, "usage: pdivert -p port [-fq]\n");
+			return 2;
+		}
+	}
+	if (port <= 0 || port > 65535) {
+		fprintf(stderr, "pdivert: -p <port> required\n");
+		return 2;
+	}
+
+	if ((fd = socket(PF_DIVERT, SOCK_RAW, IPPROTO_DIVERT)) == -1) {
+		perror("socket(PF_DIVERT)");
+		return 1;
+	}
+	{
+		struct sockaddr_in sa;
+
+		memset(&sa, 0, sizeof(sa));
+		sa.sin_family = AF_INET;	/* family ignored by bind; port only */
+		sa.sin_port = htons((uint16_t)port);
+		if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
+			perror("bind");
+			return 1;
+		}
+	}
+	if (!quiet)
+		fprintf(stderr, "pdivert: listening on divert port %d\n", port);
+
+	for (;;) {
+		ssize_t n = recv(fd, buf, sizeof(buf), 0);
+
+		if (n <= 0) {
+			if (n < 0 && errno != EAGAIN && errno != EINTR)
+				perror("recv");
+			if (n == 0)
+				break;
+			continue;
+		}
+		if (!quiet) {
+			char src[64] = "?", dst[64] = "?";
+
+			if (n >= 20 && (buf[0] >> 4) == 4) {
+				inet_ntop(AF_INET, buf + 12, src, sizeof(src));
+				inet_ntop(AF_INET, buf + 16, dst, sizeof(dst));
+			}
+			fprintf(stderr, "pdivert: got %zd bytes %s -> %s\n",
+			    n, src, dst);
+		}
+		if (flip && n > 0)
+			buf[n - 1] ^= 0xff;
+		if (send(fd, buf, (size_t)n, 0) == -1)
+			perror("send");
+	}
+	close(fd);
+	return 0;
+}