libsyslog: add multicast egress options, ABI 0.1.0 -> 0.2.0

This patch adds two new members to the syslog_data struct: - .log_iface: outbound interface for multicast destinations - .log_ttl: IP TTL value for multicast destinations When the .log_host member is set to an IPv4 or IPv6 multicast group the two new members control the behavior of egressing multicast traffic. Signed-off-by: Joachim Wiberg <[email protected]>
troglobit · Jan 2, 2025 · d880e03 · d880e03
1 parent 599bcb1
commit d880e03
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Showing 3 changed files with 47 additions and 1 deletion.
diff --git a/src/Makefile.am b/src/Makefile.am
@@ -54,7 +54,7 @@ pkgconfig_DATA        = libsyslog.pc
 pkginclude_HEADERS    = syslog.h
 libsyslog_la_SOURCES  = syslog.c syslog.h compat.h
 libsyslog_la_CPPFLAGS = $(AM_CPPFLAGS) -D_XOPEN_SOURCE=600
-libsyslog_la_LDFLAGS  = $(AM_LDFLAGS) -version-info 1:0:1
+libsyslog_la_LDFLAGS  = $(AM_LDFLAGS) -version-info 2:0:2
 libsyslog_la_LIBADD   = $(LTLIBOBJS)
 
 # Both libsyslog and syslogd/logger require objects like lib/pidfile.o.

diff --git a/src/syslog.c b/src/syslog.c
@@ -45,6 +45,8 @@ __RCSID("$NetBSD: syslog.c,v 1.55 2015/10/26 11:44:30 roy Exp $");
 #include <sys/uio.h>
 #include <sys/un.h>
 #include <netdb.h>
+#include <net/if.h>	    /* if_nametoindex() */
+#include <netinet/in.h>     /* IN_MULTICAST, IN6_IS_ADDR_MULTICAST */
 
 #include <errno.h>
 #include <fcntl.h>
@@ -110,6 +112,42 @@ static socklen_t sa_len(struct sockaddr *sa)
 }
 #endif
 
+/*
+ * Used to set outbound multicast interface and IP TTL
+ */
+static int set_mcopts(int sd, struct sockaddr *sa, char *iface, int ttl)
+{
+	int idx = 0;
+	int rc = 0;
+
+	if (iface) {
+		idx = if_nametoindex(iface);
+		if (idx == 0)
+			return -1;
+	}
+
+	if (sa->sa_family == AF_INET) {
+		struct sockaddr_in *sin = (struct sockaddr_in *)sa;
+		struct ip_mreqn imr = { .imr_ifindex = idx };
+
+		if (!IN_MULTICAST(ntohl(sin->sin_addr.s_addr)))
+			return 0;
+
+		rc += setsockopt(sd, IPPROTO_IP, IP_MULTICAST_IF, &imr, sizeof(imr));
+		rc += setsockopt(sd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
+	} else if (sa->sa_family == AF_INET6) {
+		struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sa;
+
+		if (!IN6_IS_ADDR_MULTICAST(&sin6->sin6_addr))
+			return 0;
+
+		rc += setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &idx, sizeof(idx));
+		rc += setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
+	}
+
+	return rc;
+}
+
 /*
  * syslog, vsyslog --
  *	print message on log file; output is intended for syslogd(8).
@@ -534,6 +572,7 @@ vsyslogp_r(int pri, struct syslog_data *data, const char *msgid,
 	for (tries = 0; tries < MAXTRIES; tries++) {
 		if (sendto(data->log_file, tbuf, cnt, 0, sa, len) != -1)
 			break;
+
 		if (errno != ENOBUFS) {
 			disconnectlog_r(data);
 			connectlog_r(data);
@@ -634,6 +673,9 @@ connectlog_r(struct syslog_data *data)
 			return;
 		}
 
+		/* attempt to set outbound interface for multicast & ttl */
+		set_mcopts(data->log_file, sa, data->log_iface, data->log_ttl);
+
 		if (connect(data->log_file, sa, len) == -1) {
 			(void)close(data->log_file);
 			data->log_file = -1;

diff --git a/src/syslog.h b/src/syslog.h
@@ -213,6 +213,8 @@ struct syslog_data {
 	int	log_mask;
 	void	*log_host;		/* struct sockaddr* */
 	int     log_pid;
+	char	*log_iface;		/* Multicast interface */
+	int	log_ttl;		/* Multicast TTL */
 };
 
 #define SYSLOG_DATA_INIT { \
@@ -228,6 +230,8 @@ struct syslog_data {
     .log_mask = 0xff, \
     .log_host = NULL, \
     .log_pid = -1, \
+    .log_iface = NULL, \
+    .log_ttl = 1, \
 }
 
 #ifdef __cplusplus