linux-kernel - [PATCH 4.4 317/342] should_follow_link(): validate ->d

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Message-Id: <20160301234538.121370124@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:55:30 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 4.4 317/342] should_follow_link(): validate ->d_seq after having decided to follow

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@...iv.linux.org.uk>

commit a7f775428b8f5808815c0e3004020cedb94cbe3b upstream.

... otherwise d_is_symlink() above might have nothing to do with
the inode value we've got.

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

---
 fs/namei.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1711,6 +1711,11 @@ static inline int should_follow_link(str
 		return 0;
 	if (!follow)
 		return 0;
+	/* make sure that d_is_symlink above matches inode */
+	if (nd->flags & LOOKUP_RCU) {
+		if (read_seqcount_retry(&link->dentry->d_seq, seq))
+			return -ECHILD;
+	}
 	return pick_link(nd, link, inode, seq);
 }