ep_create_wakeup_source(): dentry name can change under you...

commit 3701cb59 upstream.

or get freed, for that matter, if it's a long (separately stored)
name.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/eventpoll.c

@@ -1376,7 +1376,7 @@ static int reverse_path_check(void)
 
 static int ep_create_wakeup_source(struct epitem *epi)
 {
-	const char *name;
+	struct name_snapshot n;
 	struct wakeup_source *ws;
 
 	if (!epi->ep->ws) {
@@ -1385,8 +1385,9 @@ static int ep_create_wakeup_source(struct epitem *epi)
 			return -ENOMEM;
 	}
 
-	name = epi->ffd.file->f_path.dentry->d_name.name;
-	ws = wakeup_source_register(name);
+	take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry);
+	ws = wakeup_source_register(n.name);
+	release_dentry_name_snapshot(&n);
 
 	if (!ws)
 		return -ENOMEM;