usbip: Fix potential format overflow in userspace tools

The usbip userspace tools call sprintf()/snprintf() and don't check for
the return value which can lead the paths to overflow, truncating the
final file in the path.

More urgently, GCC 7 now warns that these aren't checked with
-Wformat-overflow, and with -Werror enabled in configure.ac, that makes
these tools unbuildable.

This patch fixes these problems by replacing sprintf() with snprintf() in
one place and adding checks for the return value of snprintf().

Reviewed-by: Peter Senna Tschudin <[e-mail]>
Signed-off-by: Jonathan Dieter <[e-mail]>
Acked-by: Shuah Khan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/usb/usbip/libsrc/usbip_common.c

···
 		       struct usbip_usb_interface *uinf)
 {
 	char busid[SYSFS_BUS_ID_SIZE];
+	int size;
 	struct udev_device *sif;
 
-	sprintf(busid, "%s:%d.%d", udev->busid, udev->bConfigurationValue, i);
+	size = snprintf(busid, sizeof(busid), "%s:%d.%d",
+			udev->busid, udev->bConfigurationValue, i);
+	if (size < 0 || (unsigned int)size >= sizeof(busid)) {
+		err("busid length %i >= %lu or < 0", size,
+		    (long unsigned)sizeof(busid));
+		return -1;
+	}
 
 	sif = udev_device_new_from_subsystem_sysname(udev_context, "usb", busid);
 	if (!sif) {

tools/usb/usbip/libsrc/usbip_host_common.c

···
 static int32_t read_attr_usbip_status(struct usbip_usb_device *udev)
 {
 	char status_attr_path[SYSFS_PATH_MAX];
+	int size;
 	int fd;
 	int length;
 	char status;
 	int value = 0;
 
-	snprintf(status_attr_path, SYSFS_PATH_MAX, "%s/usbip_status",
-		 udev->path);
+	size = snprintf(status_attr_path, sizeof(status_attr_path),
+			"%s/usbip_status", udev->path);
+	if (size < 0 || (unsigned int)size >= sizeof(status_attr_path)) {
+		err("usbip_status path length %i >= %lu or < 0", size,
+		    (long unsigned)sizeof(status_attr_path));
+		return -1;
+	}
+
 
 	fd = open(status_attr_path, O_RDONLY);
 	if (fd < 0) {
···
 {
 	char attr_name[] = "usbip_sockfd";
 	char sockfd_attr_path[SYSFS_PATH_MAX];
+	int size;
 	char sockfd_buff[30];
 	int ret;
 
···
 	}
 
 	/* only the first interface is true */
-	snprintf(sockfd_attr_path, sizeof(sockfd_attr_path), "%s/%s",
-		 edev->udev.path, attr_name);
+	size = snprintf(sockfd_attr_path, sizeof(sockfd_attr_path), "%s/%s",
+			edev->udev.path, attr_name);
+	if (size < 0 || (unsigned int)size >= sizeof(sockfd_attr_path)) {
+		err("exported device path length %i >= %lu or < 0", size,
+		    (long unsigned)sizeof(sockfd_attr_path));
+		return -1;
+	}
 
-	snprintf(sockfd_buff, sizeof(sockfd_buff), "%d\n", sockfd);
+	size = snprintf(sockfd_buff, sizeof(sockfd_buff), "%d\n", sockfd);
+	if (size < 0 || (unsigned int)size >= sizeof(sockfd_buff)) {
+		err("socket length %i >= %lu or < 0", size,
+		    (long unsigned)sizeof(sockfd_buff));
+		return -1;
+	}
 
 	ret = write_sysfs_attribute(sockfd_attr_path, sockfd_buff,
 				    strlen(sockfd_buff));