Add support for PACKET_FANOUT on Linux

This work is based on PR #674 while taking into consideration the review
comments which caused the PR to be closed by the original author,
@xpahos.

CMakeLists.txt

@@ -2619,6 +2619,7 @@ set(MAN3PCAP_NOEXPAND
     pcap_open_live.3pcap
     pcap_set_buffer_size.3pcap
     pcap_set_datalink.3pcap
+    pcap_set_fanout_linux.3pcap
     pcap_set_promisc.3pcap
     pcap_set_protocol_linux.3pcap
     pcap_set_rfmon.3pcap

CREDITS

@@ -169,6 +169,8 @@ Additional people who have contributed patches (in alphabetical order):
     Nick Kelsey                   <nickk at silicondust dot com>
     Nicolas Dade                  <ndade at nsd dot dyndns dot org>
     Niko Delarich                 <niko dot delarich at gmail dot com>
+    Noam Meltzer                  <noam at cynerio dot co>
+                                  <tsnoam at gmail dot com>
     N. Leiten                     <nleiten at sourceforge dot net>
     nnposter                      <nnposter at users dot noreply dot github dot com>
                                   <nvercamm at sourceforge dot net>

Makefile.in

@@ -216,6 +216,7 @@ MAN3PCAP_NOEXPAND = \
 	pcap_open_live.3pcap \
 	pcap_set_buffer_size.3pcap \
 	pcap_set_datalink.3pcap \
+	pcap_set_fanout_linux.3pcap \
 	pcap_set_promisc.3pcap \
 	pcap_set_protocol_linux.3pcap \
 	pcap_set_rfmon.3pcap \

pcap-int.h

@@ -176,6 +176,8 @@ struct pcap_opt {
 	 */
 #ifdef __linux__
 	int	protocol;	/* protocol to use when creating PF_PACKET socket */
+	int	fanout_enabled;	/* If evaluates to TRUE, fanout mode is enabled; default: FALSE. */
+	int	fanout_opt;	/* 16 lower bits are the group id; upper bits are the mode. */
 #endif
 #ifdef _WIN32
 	int	nocapture_local;/* disable NPF loopback */

pcap-linux.c

@@ -224,6 +224,7 @@ static void map_arphrd_to_dlt(pcap_t *, int, const char *, int);
 static int pcap_activate_linux(pcap_t *);
 static int activate_pf_packet(pcap_t *, int);
 static int setup_mmapped(pcap_t *, int *);
+static int activate_fanout(pcap_t *);
 static int pcap_can_set_rfmon_linux(pcap_t *);
 static int pcap_inject_linux(pcap_t *, const void *, int);
 static int pcap_stats_linux(pcap_t *, struct pcap_stat *);
@@ -1076,6 +1077,16 @@ pcap_activate_linux(pcap_t *handle)
 		goto fail;
 	}
 
+	/*
+	 * Only after we have the socket properly binded and set with the
+	 * correct protocol we can set the FANOUT mode.
+	 */
+	if ((status2 = activate_fanout(handle)) != 0) {
+		status = status2;
+		goto fail;
+	}
+
+
 	handle->inject_op = pcap_inject_linux;
 	handle->setfilter_op = pcap_setfilter_linux;
 	handle->setdirection_op = pcap_setdirection_linux;
@@ -2281,8 +2292,8 @@ activate_pf_packet(pcap_t *handle, int is_any_device)
 	const char		*device = handle->opt.device;
 	int			status = 0;
 	int			sock_fd, arptype;
-#ifdef HAVE_PACKET_AUXDATA
-	int			val;
+#if defined(HAVE_PACKET_AUXDATA)
+	int			val = 0;
 #endif
 	int			err = 0;
 	struct packet_mreq	mr;
@@ -2644,6 +2655,30 @@ activate_pf_packet(pcap_t *handle, int is_any_device)
 	return status;
 }
 
+/*
+ * Add the packet socket into FANOUT group, if needed.
+ *
+ * On success (or if nothing was done), returns 0.
+ *
+ * On error, returns -1 and sets handle->errbuf to the appropriate message.
+ */
+static int
+activate_fanout(pcap_t *handle) {
+	int rc = 0;
+#ifdef PACKET_FANOUT
+	int val = handle->opt.fanout_opt;
+
+	if (handle->opt.fanout_enabled &&
+	    setsockopt(handle->fd, SOL_PACKET, PACKET_FANOUT, &val, sizeof(val)) < 0) {
+		pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE, errno, "setsockopt (PACKET_FANOUT)");
+		rc = -1;
+	}
+#endif /* PACKET_FANOUT */
+
+	return rc;
+}
+
+
 /*
  * Attempt to setup memory-mapped access.
  *
@@ -5421,6 +5456,25 @@ pcap_set_protocol_linux(pcap_t *p, int protocol)
 	return (0);
 }
 
+int
+pcap_set_fanout_linux(pcap_t *p, int enable, uint16_t mode, uint16_t group_id)
+{
+#ifdef PACKET_FANOUT
+	if (pcap_check_activated(p)) {
+		return (PCAP_ERROR_ACTIVATED);
+	}
+
+	p->opt.fanout_enabled = enable;
+	p->opt.fanout_opt = (((int)mode) << 16) | ((int)group_id & 0xffff);
+
+	return 0;
+#else
+	pcap_fmt_errmsg_for_errno(p->errbuf, PCAP_ERRBUF_SIZE,
+	    errno, "fanout is not supported");
+	return -1;
+#endif
+}
+
 /*
  * Libpcap version string.
  */

pcap.c

@@ -2520,6 +2520,8 @@ pcap_create_common(char *ebuf, size_t total_size, size_t private_offset)
 	 */
 #ifdef __linux__
 	p->opt.protocol = 0;
+	p->opt.fanout_enabled = 0;
+	p->opt.fanout_opt = 0;
 #endif
 #ifdef _WIN32
 	p->opt.nocapture_local = 0;

pcap/pcap.h

@@ -451,6 +451,7 @@ PCAP_API const char *pcap_tstamp_type_val_to_description(int);
 #ifdef __linux__
 PCAP_AVAILABLE_1_9
 PCAP_API int	pcap_set_protocol_linux(pcap_t *, int);
+PCAP_API int	pcap_set_fanout_linux(pcap_t *, int, uint16_t, uint16_t);
 #endif
 
 /*

pcap_set_fanout_linux.3pcap

@@ -0,0 +1,76 @@
+.\" Copyright (c) 1994, 1996, 1997
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that: (1) source code distributions
+.\" retain the above copyright notice and this paragraph in its entirety, (2)
+.\" distributions including binary code include the above copyright notice and
+.\" this paragraph in its entirety in the documentation or other materials
+.\" provided with the distribution, and (3) all advertising materials mentioning
+.\" features or use of this software display the following acknowledgement:
+.\" ``This product includes software developed by the University of California,
+.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
+.\" the University nor the names of its contributors may be used to endorse
+.\" or promote products derived from this software without specific prior
+.\" written permission.
+.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+.\"
+.TH PCAP_SET_FANOUT 3PCAP "16 April 2020"
+.SH NAME
+pcap_set_fanout_linux \- set fanout group for load balancing
+among processes
+.SH SYNOPSIS
+.nf
+.ft B
+#include <linux/if_packet.h>
+#include <pcap/pcap.h>
+.LP
+.ft B
+int pcap_set_fanout_linux(pcap_t *p, int enable, uint16_t mode, uint16_t group_id);
+.ft
+.fi
+.SH DESCRIPTION
+On Linux network interface devices,
+.B pcap_set_fanout_linux()
+sets the fanout configuration to be used in the
+.BR socket (2)
+call to create a capture socket when the handle is activated.
+.LP
+Using fanout is required if you want to load-balance multiple processes and/or
+threads to handle the intercepted traffic. When preparing the socket to be used,
+it is required to set a group_id in order to distinguish between different
+consumers.
+.LP
+A single fanout groups load-balances the handling of intercepted traffic.
+.LP
+It is possible to have any combination of fanout groups or "normal" consumers,
+as it is possible with only "normal" consumers ("normal" - non fanout).
+.LP
+This function is only provided on Linux, and, if it is used on any device other
+than a network interface, it will have no effect.
+.LP
+.IR enable
+is a boolean flag to control if fanout is enabled (default is FALSE).
+.LP
+.IR mode
+is the fanout mode and flags to use. More information on the various modes can
+be found in
+.BR packet (7)\c
+\&.
+.LP
+.IR group_id
+is a unique identifier of the socket group.
+.LP
+.BR pcap_set_fanout_linux()
+should not be used in portable code.
+
+.SH RETURN VALUE
+Returns 0 on success or
+.B PCAP_ERROR_ACTIVATED
+if called on a capture handle that has been activated.
+.SH SEE ALSO
+.BR pcap (3PCAP)
+.BR socket (2)
+.BR packet (7)