From f6a58b60af9220fa23e7361328f99c7902e2fc06 Mon Sep 17 00:00:00 2001
From: Bram Matthys <syzop@vulnscan.org>
Date: Wed, 9 Dec 2015 17:44:54 +0100
Subject: [PATCH] Added workaround for "Cannot accept connections: Operation
 not supported" problem (#4469).

---
 include/h.h  |  1 +
 src/s_bsd.c  | 25 +++++++++++++++++++------
 src/s_conf.c | 12 +++++++-----
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/include/h.h b/include/h.h
index e11d45187..b4e1386b5 100644
--- a/include/h.h
+++ b/include/h.h
@@ -754,3 +754,4 @@ extern MODVAR aClient *remote_rehash_client;
 extern MODVAR int debugfd;
 extern void convert_to_absolute_path(char **path, char *reldir);
 extern int has_channel_mode(aChannel *chptr, char mode);
+extern void start_listeners(void);
diff --git a/src/s_bsd.c b/src/s_bsd.c
index 04972ae4d..35cf1ac25 100644
--- a/src/s_bsd.c
+++ b/src/s_bsd.c
@@ -95,6 +95,7 @@ void completed_connection(int, int, void *);
 static int check_init(aClient *, char *, size_t);
 void set_sock_opts(int, aClient *, int);
 void set_ipv6_opts(int);
+void close_listener(ConfigItem_listen *listener);
 static char readbuf[BUFSIZE];
 char zlinebuf[BUFSIZE];
 extern char *version;
@@ -285,19 +286,31 @@ void report_baderror(char *text, aClient *cptr)
 /** Accept an incoming client. */
 static void listener_accept(int listener_fd, int revents, void *data)
 {
-	ConfigItem_listen *cptr = data;
+	ConfigItem_listen *listener = data;
 	int cli_fd;
 
-	if ((cli_fd = fd_accept(cptr->fd)) < 0)
+	if ((cli_fd = fd_accept(listener->fd)) < 0)
 	{
-	        if ((ERRNO != P_EWOULDBLOCK) && (ERRNO != P_ECONNABORTED))
+		if ((ERRNO != P_EWOULDBLOCK) && (ERRNO != P_ECONNABORTED))
+		{
+			/* Trouble! accept() returns a strange error.
+			 * Previously in such a case we would just log/broadcast the error and return,
+			 * causing this message to be triggered at a rate of XYZ per second (100% CPU).
+			 * Now we close & re-start the listener.
+			 * Of course the underlying cause of this issue should be investigated, as this
+			 * is very much a workaround.
+			 */
 			report_baderror("Cannot accept connections %s:%s", NULL);
+			sendto_realops("[BUG] Restarting listener on %s:%d due to fatal errors (see previous message)", listener->ip, listener->port);
+			close_listener(listener);
+			start_listeners();
+		}
 		return;
 	}
 
 	ircstp->is_ac++;
 
-	set_sock_opts(cli_fd, NULL, cptr->ipv6);
+	set_sock_opts(cli_fd, NULL, listener->ipv6);
 	set_non_blocking(cli_fd, NULL);
 
 	if ((++OpenFiles >= MAXCLIENTS) || (cli_fd >= MAXCLIENTS))
@@ -305,7 +318,7 @@ static void listener_accept(int listener_fd, int revents, void *data)
 		ircstp->is_ref++;
 		if (last_allinuse < TStime() - 15)
 		{
-			sendto_realops("All connections in use. ([@%s/%u])", cptr->ip, cptr->port);
+			sendto_realops("All connections in use. ([@%s/%u])", listener->ip, listener->port);
 			last_allinuse = TStime();
 		}
 
@@ -317,7 +330,7 @@ static void listener_accept(int listener_fd, int revents, void *data)
 	}
 
 	/* add_connection() may fail. we just don't care. */
-	(void)add_connection(cptr, cli_fd);
+	(void)add_connection(listener, cli_fd);
 }
 
 /*
diff --git a/src/s_conf.c b/src/s_conf.c
index 7547e6dbf..cd10db150 100644
--- a/src/s_conf.c
+++ b/src/s_conf.c
@@ -8087,11 +8087,7 @@ int	_test_loadmodule(ConfigFile *conf, ConfigEntry *ce)
 	return 0;
 }
 
-/*
- * Actually use configuration
-*/
-
-void	run_configuration(void)
+void start_listeners(void)
 {
 	ConfigItem_listen 	*listenptr;
 	int failed = 0, ports_bound = 0;
@@ -8164,6 +8160,12 @@ void	run_configuration(void)
 	}
 }
 
+/* Actually use configuration */
+void run_configuration(void)
+{
+	start_listeners();
+}
+
 int	_conf_offchans(ConfigFile *conf, ConfigEntry *ce)
 {
 	ConfigEntry *cep, *cepp;