net: context: connect: Make sure local end is bound before connecting

Introduce net_context_bind_default() to ensure that local address is
set for context if not yet (via explict bind() call). This fixes
dereferences of NULL pointer to local address which was exposed when
MMU was enabled for qemu_x86.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>

subsys/net/ip/net_context.c

@@ -689,6 +689,53 @@ int net_context_put(struct net_context *context)
 	return 0;
 }
 
+/* If local address is not bound, bind it to INADDR_ANY and random port. */
+static int bind_default(struct net_context *context)
+{
+	sa_family_t family = net_context_get_family(context);
+
+#if defined(CONFIG_NET_IPV6)
+	if (family == AF_INET6) {
+		struct sockaddr_in6 addr6;
+
+		if (net_sin6_ptr(&context->local)->sin6_addr) {
+			return 0;
+		}
+
+		addr6.sin6_family = AF_INET6;
+		memcpy(&addr6.sin6_addr, net_ipv6_unspecified_address(),
+		       sizeof(addr6.sin6_addr));
+		addr6.sin6_port =
+			find_available_port(context,
+					    (struct sockaddr *)&addr6);
+
+		return net_context_bind(context, (struct sockaddr *)&addr6,
+					sizeof(addr6));
+	}
+#endif
+
+#if defined(CONFIG_NET_IPV4)
+	if (family == AF_INET) {
+		struct sockaddr_in addr4;
+
+		if (net_sin_ptr(&context->local)->sin_addr) {
+			return 0;
+		}
+
+		addr4.sin_family = AF_INET;
+		addr4.sin_addr.s_addr = INADDR_ANY;
+		addr4.sin_port =
+			find_available_port(context,
+					    (struct sockaddr *)&addr4);
+
+		return net_context_bind(context, (struct sockaddr *)&addr4,
+					sizeof(addr4));
+	}
+#endif
+
+	return -EINVAL;
+}
+
 int net_context_bind(struct net_context *context, const struct sockaddr *addr,
 		     socklen_t addrlen)
 {
@@ -1331,8 +1378,8 @@ int net_context_connect(struct net_context *context,
 	struct sockaddr *laddr = NULL;
 	struct sockaddr local_addr;
 	u16_t lport, rport;
-	int ret;
 #endif
+	int ret;
 
 	NET_ASSERT(addr);
 	NET_ASSERT(PART_OF_ARRAY(contexts, context));
@@ -1344,6 +1391,11 @@ int net_context_connect(struct net_context *context,
 		return -EBADF;
 	}
 
+	ret = bind_default(context);
+	if (ret) {
+		return ret;
+	}
+
 	if (addr->family != net_context_get_family(context)) {
 		NET_ASSERT_INFO(addr->family == \
 				net_context_get_family(context),