[Dnsmasq-discuss] [PATCH] Only bind IPv6 wildcard when it is enabled

[Matthias May]

On Linux when IPv6 is disabled, one would not expect Dnsmasq to bind
the IPv6 wildcard.
This patch adds a condition to the wildcard bind function, which checks
on Linux if IPv6 is disabled.

Signed-off-by: Matthias May <matthias.may at westermo.com>
Signed-off-by: Zefir Kurtisi <zefir.kurtisi at westermo.com>
---
 src/dnsmasq.h |  1 +
 src/network.c | 24 +++++++++++++-----------
 src/util.c    | 22 ++++++++++++++++++++++
 3 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 4220798..2cfb1cb 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -1292,6 +1292,7 @@ int read_write(int fd, unsigned char *packet, int size, int rw);
 void close_fds(long max_fd, int spare1, int spare2, int spare3);
 int wildcard_match(const char* wildcard, const char* match);
 int wildcard_matchn(const char* wildcard, const char* match, int num);
+int is_ipv6_disabled(void);
 #ifdef HAVE_LINUX_NETWORK
 int kernel_version(void);
 #endif
diff --git a/src/network.c b/src/network.c
index c7d002b..0d35fb7 100644
--- a/src/network.c
+++ b/src/network.c
@@ -990,19 +990,21 @@ void create_wildcard_listeners(void)
 
   l = create_listeners(&addr, !!option_bool(OPT_TFTP), 1);
 
-  memset(&addr, 0, sizeof(addr));
+  if (!is_ipv6_disabled()) {
+    memset(&addr, 0, sizeof(addr));
 #ifdef HAVE_SOCKADDR_SA_LEN
-  addr.in6.sin6_len = sizeof(addr.in6);
+    addr.in6.sin6_len = sizeof(addr.in6);
 #endif
-  addr.in6.sin6_family = AF_INET6;
-  addr.in6.sin6_addr = in6addr_any;
-  addr.in6.sin6_port = htons(daemon->port);
- 
-  l6 = create_listeners(&addr, !!option_bool(OPT_TFTP), 1);
-  if (l) 
-    l->next = l6;
-  else 
-    l = l6;
+    addr.in6.sin6_family = AF_INET6;
+    addr.in6.sin6_addr = in6addr_any;
+    addr.in6.sin6_port = htons(daemon->port);
+
+    l6 = create_listeners(&addr, !!option_bool(OPT_TFTP), 1);
+    if (l)
+      l->next = l6;
+    else
+      l = l6;
+  }
 
   daemon->listeners = l;
 }
diff --git a/src/util.c b/src/util.c
index 5f13027..5cd461f 100644
--- a/src/util.c
+++ b/src/util.c
@@ -787,6 +787,28 @@ int wildcard_matchn(const char* wildcard, const char* match, int num)
   return (!num) || (*wildcard == *match);
 }
 
+#ifndef HAVE_LINUX_NETWORK
+/* implement for other platforms */
+int is_ipv6_disabled(void)
+{
+	return 0;
+}
+#else /* HAVE_LINUX_NETWORK */
+int is_ipv6_disabled(void)
+{
+	FILE *f;
+	char *fname = "/proc/sys/net/ipv6/conf/all/disable_ipv6";
+	char buf[4];
+	int ipv6_disabled = 0;
+	if ((f = fopen(fname, "r"))) {
+		if (fgets(buf, 4, f))
+			ipv6_disabled = atoi(buf) == 1;
+		fclose(f);
+	}
+	return ipv6_disabled;
+}
+#endif /* HAVE_LINUX_NETWORK */
+
 #ifdef HAVE_LINUX_NETWORK
 int kernel_version(void)
 {
-- 
2.27.0