libudev: monitor - ignore messages from unusual sources

For added protection, ignore any unicast message received on the
netlink socket or any multicast message on the kernel group not
received from the kernel.

Signed-off-by: Scott James Remnant <scott@ubuntu.com>

1 files changed, 23 insertions, 6 deletions

diff --git a/udev/lib/libudev-monitor.c b/udev/lib/libudev-monitor.c
index 21bd19ba03..79627ed4a4 100644
--- a/udev/lib/libudev-monitor.c
+++ b/udev/lib/libudev-monitor.c
@@ -260,6 +260,7 @@ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monito
 	struct iovec iov;
 	char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 	struct cmsghdr *cmsg;
+	struct sockaddr_nl snl;
 	struct ucred *cred;
 	char buf[4096];
 	size_t bufpos;
@@ -280,34 +281,50 @@ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monito
 	smsg.msg_control = cred_msg;
 	smsg.msg_controllen = sizeof(cred_msg);
 
+	if (udev_monitor->snl.nl_family != 0) {
+		smsg.msg_name = &snl;
+		smsg.msg_namelen = sizeof snl;
+	}
+
 	if (recvmsg(udev_monitor->sock, &smsg, 0) < 0) {
 		if (errno != EINTR)
-			info(udev_monitor->udev, "unable to receive message");
+			info(udev_monitor->udev, "unable to receive message\n");
 		return NULL;
 	}
 
+	if (udev_monitor->snl.nl_family != 0) {
+		if (snl.nl_groups == 0) {
+			info(udev_monitor->udev, "unicast netlink message ignored\n");
+			return NULL;
+		}
+		if ((snl.nl_groups == UDEV_MONITOR_KERNEL) && (snl.nl_pid > 0)) {
+			info(udev_monitor->udev, "multicast kernel netlink message from pid %d ignored\n", snl.nl_pid);
+			return NULL;
+		}
+	}
+
 	cmsg = CMSG_FIRSTHDR(&smsg);
 	if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
-		info(udev_monitor->udev, "no sender credentials received, message ignored");
+		info(udev_monitor->udev, "no sender credentials received, message ignored\n");
 		return NULL;
 	}
 
 	cred = (struct ucred *)CMSG_DATA(cmsg);
 	if (cred->uid != 0) {
-		info(udev_monitor->udev, "sender uid=%d, message ignored", cred->uid);
+		info(udev_monitor->udev, "sender uid=%d, message ignored\n", cred->uid);
 		return NULL;
 	}
 
 	/* skip header */
 	bufpos = strlen(buf) + 1;
 	if (bufpos < sizeof("a@/d") || bufpos >= sizeof(buf)) {
-		info(udev_monitor->udev, "invalid message length");
+		info(udev_monitor->udev, "invalid message length\n");
 		return NULL;
 	}
 
 	/* check message header */
 	if (strstr(buf, "@/") == NULL) {
-		info(udev_monitor->udev, "unrecognized message header");
+		info(udev_monitor->udev, "unrecognized message header\n");
 		return NULL;
 	}
 
@@ -414,6 +431,6 @@ int udev_monitor_send_device(struct udev_monitor *udev_monitor, struct udev_devi
 	else
 		return -1;
 
-	info(udev_monitor->udev, "passed %zi bytes to monitor %p, \n", count, udev_monitor);
+	info(udev_monitor->udev, "passed %zi bytes to monitor %p\n", count, udev_monitor);
 	return count;
 }