From dac6c7c575ac2f8f04706a137e703deffbf88aa7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20=C5=A0tetiar?= <ynezz@true.cz>
Date: Thu, 19 Dec 2019 11:10:46 +0100
Subject: [PATCH] ubusd_monitor: fix possible null pointer dereference
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This dereference could possibly happen if the calloc call fails as the
return value is unchecked. While at it refactor the code little bit to
make it easier to follow, use safe list iterator and provide return
value for ubusd_monitor_connect.

Signed-off-by: Petr Štetiar <ynezz@true.cz>
---
 ubusd_monitor.c | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/ubusd_monitor.c b/ubusd_monitor.c
index fcbc6a4..501e06d 100644
--- a/ubusd_monitor.c
+++ b/ubusd_monitor.c
@@ -29,7 +29,7 @@ ubusd_monitor_free(struct ubus_monitor *m)
 	free(m);
 }
 
-static void
+static bool
 ubusd_monitor_connect(struct ubus_client *cl, struct ubus_msg_buf *ub)
 {
 	struct ubus_monitor *m;
@@ -37,8 +37,28 @@ ubusd_monitor_connect(struct ubus_client *cl, struct ubus_msg_buf *ub)
 	ubusd_monitor_disconnect(cl);
 
 	m = calloc(1, sizeof(*m));
+	if (!m)
+		return false;
+
 	m->cl = cl;
 	list_add(&m->list, &monitors);
+
+	return true;
+}
+
+static struct ubus_monitor*
+ubusd_monitor_find(struct ubus_client *cl)
+{
+	struct ubus_monitor *m, *tmp;
+
+	list_for_each_entry_safe(m, tmp, &monitors, list) {
+		if (m->cl != cl)
+			continue;
+
+		return m;
+	}
+
+	return NULL;
 }
 
 void
@@ -46,13 +66,11 @@ ubusd_monitor_disconnect(struct ubus_client *cl)
 {
 	struct ubus_monitor *m;
 
-	list_for_each_entry(m, &monitors, list) {
-		if (m->cl != cl)
-			continue;
-
-		ubusd_monitor_free(m);
+	m = ubusd_monitor_find(cl);
+	if (!m)
 		return;
-	}
+
+	ubusd_monitor_free(m);
 }
 
 void
@@ -92,13 +110,15 @@ ubusd_monitor_recv(struct ubus_client *cl, struct ubus_msg_buf *ub,
 		return UBUS_STATUS_PERMISSION_DENIED;
 
 	if (!strcmp(method, "add")) {
-		ubusd_monitor_connect(cl, ub);
-		return 0;
+		if (!ubusd_monitor_connect(cl, ub))
+			return UBUS_STATUS_UNKNOWN_ERROR;
+
+		return UBUS_STATUS_OK;
 	}
 
 	if (!strcmp(method, "remove")) {
 		ubusd_monitor_disconnect(cl);
-		return 0;
+		return UBUS_STATUS_OK;
 	}
 
 	return UBUS_STATUS_METHOD_NOT_FOUND;