fwd: Rename port_fwd.[ch] and their contents

Currently port_fwd.[ch] contains helpers related to port forwarding,
particular automatic port forwarding.  We're planning to allow much more
flexible sorts of forwarding, including both port translation and NAT based
on the flow table.  This will subsume the existing port forwarding logic,
so rename port_fwd.[ch] to fwd.[ch] with matching updates to all the names
within.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 155 insertions, 0 deletions

diff --git a/fwd.c b/fwd.c
new file mode 100644
index 0000000..09650b2
--- /dev/null
+++ b/fwd.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *  for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ *  for network namespace/tap device mode
+ *
+ * fwd.c - Port forwarding helpers
+ *
+ * Copyright Red Hat
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+
+#include <stdint.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#include "util.h"
+#include "fwd.h"
+#include "passt.h"
+#include "lineread.h"
+
+/* See enum in kernel's include/net/tcp_states.h */
+#define UDP_LISTEN	0x07
+#define TCP_LISTEN	0x0a
+
+/**
+ * procfs_scan_listen() - Set bits for listening TCP or UDP sockets from procfs
+ * @fd:		fd for relevant /proc/net file
+ * @lstate:	Code for listening state to scan for
+ * @map:	Bitmap where numbers of ports in listening state will be set
+ * @exclude:	Bitmap of ports to exclude from setting (and clear)
+ *
+ * #syscalls:pasta lseek
+ * #syscalls:pasta ppc64le:_llseek ppc64:_llseek armv6l:_llseek armv7l:_llseek
+ */
+static void procfs_scan_listen(int fd, unsigned int lstate,
+			       uint8_t *map, const uint8_t *exclude)
+{
+	struct lineread lr;
+	unsigned long port;
+	unsigned int state;
+	char *line;
+
+	if (fd < 0)
+		return;
+
+	if (lseek(fd, 0, SEEK_SET)) {
+		warn("lseek() failed on /proc/net file: %s", strerror(errno));
+		return;
+	}
+
+	lineread_init(&lr, fd);
+	lineread_get(&lr, &line); /* throw away header */
+	while (lineread_get(&lr, &line) > 0) {
+		/* NOLINTNEXTLINE(cert-err34-c): != 2 if conversion fails */
+		if (sscanf(line, "%*u: %*x:%lx %*x:%*x %x", &port, &state) != 2)
+			continue;
+
+		if (state != lstate)
+			continue;
+
+		if (bitmap_isset(exclude, port))
+			bitmap_clear(map, port);
+		else
+			bitmap_set(map, port);
+	}
+}
+
+/**
+ * fwd_scan_ports_tcp() - Scan /proc to update TCP forwarding map
+ * @fwd:	Forwarding information to update
+ * @rev:	Forwarding information for the reverse direction
+ */
+void fwd_scan_ports_tcp(struct fwd_ports *fwd, const struct fwd_ports *rev)
+{
+	memset(fwd->map, 0, PORT_BITMAP_SIZE);
+	procfs_scan_listen(fwd->scan4, TCP_LISTEN, fwd->map, rev->map);
+	procfs_scan_listen(fwd->scan6, TCP_LISTEN, fwd->map, rev->map);
+}
+
+/**
+ * fwd_scan_ports_udp() - Scan /proc to update UDP forwarding map
+ * @fwd:	Forwarding information to update
+ * @rev:	Forwarding information for the reverse direction
+ * @tcp_fwd:	Corresponding TCP forwarding information
+ * @tcp_rev:	TCP forwarding information for the reverse direction
+ */
+void fwd_scan_ports_udp(struct fwd_ports *fwd, const struct fwd_ports *rev,
+			const struct fwd_ports *tcp_fwd,
+			const struct fwd_ports *tcp_rev)
+{
+	uint8_t exclude[PORT_BITMAP_SIZE];
+
+	bitmap_or(exclude, PORT_BITMAP_SIZE, rev->map, tcp_rev->map);
+
+	memset(fwd->map, 0, PORT_BITMAP_SIZE);
+	procfs_scan_listen(fwd->scan4, UDP_LISTEN, fwd->map, exclude);
+	procfs_scan_listen(fwd->scan6, UDP_LISTEN, fwd->map, exclude);
+
+	/* Also forward UDP ports with the same numbers as bound TCP ports.
+	 * This is useful for a handful of protocols (e.g. iperf3) where a TCP
+	 * control port is used to set up transfers on a corresponding UDP
+	 * port.
+	 *
+	 * This means we need to skip numbers of TCP ports bound on the other
+	 * side, too. Otherwise, we would detect corresponding UDP ports as
+	 * bound and try to forward them from the opposite side, but it's
+	 * already us handling them.
+	 */
+	procfs_scan_listen(tcp_fwd->scan4, TCP_LISTEN, fwd->map, exclude);
+	procfs_scan_listen(tcp_fwd->scan6, TCP_LISTEN, fwd->map, exclude);
+}
+
+/**
+ * fwd_scan_ports_init() - Initial setup for automatic port forwarding
+ * @c:		Execution context
+ */
+void fwd_scan_ports_init(struct ctx *c)
+{
+	const int flags = O_RDONLY | O_CLOEXEC;
+
+	c->tcp.fwd_in.scan4 = c->tcp.fwd_in.scan6 = -1;
+	c->tcp.fwd_out.scan4 = c->tcp.fwd_out.scan6 = -1;
+	c->udp.fwd_in.f.scan4 = c->udp.fwd_in.f.scan6 = -1;
+	c->udp.fwd_out.f.scan4 = c->udp.fwd_out.f.scan6 = -1;
+
+	if (c->tcp.fwd_in.mode == FWD_AUTO) {
+		c->tcp.fwd_in.scan4 = open_in_ns(c, "/proc/net/tcp", flags);
+		c->tcp.fwd_in.scan6 = open_in_ns(c, "/proc/net/tcp6", flags);
+		fwd_scan_ports_tcp(&c->tcp.fwd_in, &c->tcp.fwd_out);
+	}
+	if (c->udp.fwd_in.f.mode == FWD_AUTO) {
+		c->udp.fwd_in.f.scan4 = open_in_ns(c, "/proc/net/udp", flags);
+		c->udp.fwd_in.f.scan6 = open_in_ns(c, "/proc/net/udp6", flags);
+		fwd_scan_ports_udp(&c->udp.fwd_in.f, &c->udp.fwd_out.f,
+				   &c->tcp.fwd_in, &c->tcp.fwd_out);
+	}
+	if (c->tcp.fwd_out.mode == FWD_AUTO) {
+		c->tcp.fwd_out.scan4 = open("/proc/net/tcp", flags);
+		c->tcp.fwd_out.scan6 = open("/proc/net/tcp6", flags);
+		fwd_scan_ports_tcp(&c->tcp.fwd_out, &c->tcp.fwd_in);
+	}
+	if (c->udp.fwd_out.f.mode == FWD_AUTO) {
+		c->udp.fwd_out.f.scan4 = open("/proc/net/udp", flags);
+		c->udp.fwd_out.f.scan6 = open("/proc/net/udp6", flags);
+		fwd_scan_ports_udp(&c->udp.fwd_out.f, &c->udp.fwd_in.f,
+				   &c->tcp.fwd_out, &c->tcp.fwd_in);
+	}
+}