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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH 4.9 21/54] ep_create_wakeup_source(): dentry name can change under you...
Date:   Mon, 12 Oct 2020 15:26:43 +0200
Message-Id: <20201012132630.569922401@linuxfoundation.org>
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From: Al Viro <viro@zeniv.linux.org.uk>

commit 3701cb59d892b88d569427586f01491552f377b1 upstream.

or get freed, for that matter, if it's a long (separately stored)
name.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/eventpoll.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1260,7 +1260,7 @@ 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) {
@@ -1269,8 +1269,9 @@ static int ep_create_wakeup_source(struc
 			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;