cgroup: fix possible memory leak

There's a leak if copy_from_user() returns failure.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/cgroup.c

@@ -1424,14 +1424,17 @@ static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
 		if (buffer == NULL)
 			return -ENOMEM;
 	}
-	if (nbytes && copy_from_user(buffer, userbuf, nbytes))
-		return -EFAULT;
+	if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
+		retval = -EFAULT;
+		goto out;
+	}
 
 	buffer[nbytes] = 0;     /* nul-terminate */
 	strstrip(buffer);
 	retval = cft->write_string(cgrp, cft, buffer);
 	if (!retval)
 		retval = nbytes;
+out:
 	if (buffer != local_buffer)
 		kfree(buffer);
 	return retval;