linux-kernel - [PATCH 4.2.y-ckt 217/273] should_follow_link(): validate ->d

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Message-Id: <1457391064-6660-218-git-send-email-kamal@canonical.com>
Date:	Mon,  7 Mar 2016 14:50:08 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 217/273] should_follow_link(): validate ->d_seq after having decided to follow

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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: Kamal Mostafa <kamal@...onical.com>
---
 fs/namei.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 1047096..414561f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1714,6 +1714,11 @@ static inline int should_follow_link(struct nameidata *nd, struct path *link,
 		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);
 }
 
-- 
2.7.0