usbip: fix usbip bind writing random string after command in match_busid

BugLink: http://bugs.launchpad.net/bugs/1745069

commit 544c4605 upstream.

usbip bind writes commands followed by random string when writing to
match_busid attribute in sysfs, caused by using full variable size
instead of string length.
Signed-off-by: Juan Zea <juan.zea@qindel.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

tools/usb/usbip/src/utils.c

@@ -30,6 +30,7 @@ int modify_match_busid(char *busid, int add)
 	char command[SYSFS_BUS_ID_SIZE + 4];
 	char match_busid_attr_path[SYSFS_PATH_MAX];
 	int rc;
+	int cmd_size;
 
 	snprintf(match_busid_attr_path, sizeof(match_busid_attr_path),
 		 "%s/%s/%s/%s/%s/%s", SYSFS_MNT_PATH, SYSFS_BUS_NAME,
@@ -37,12 +38,14 @@ int modify_match_busid(char *busid, int add)
 		 attr_name);
 
 	if (add)
-		snprintf(command, SYSFS_BUS_ID_SIZE + 4, "add %s", busid);
+		cmd_size = snprintf(command, SYSFS_BUS_ID_SIZE + 4, "add %s",
+				    busid);
 	else
-		snprintf(command, SYSFS_BUS_ID_SIZE + 4, "del %s", busid);
+		cmd_size = snprintf(command, SYSFS_BUS_ID_SIZE + 4, "del %s",
+				    busid);
 
 	rc = write_sysfs_attribute(match_busid_attr_path, command,
-				   sizeof(command));
+				   cmd_size);
 	if (rc < 0) {
 		dbg("failed to write match_busid: %s", strerror(errno));
 		return -1;