[4.2.y-ckt stable] Patch "should_follow_link(): validate ->d_seq after having decided to follow" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    should_follow_link(): validate ->d_seq after having decided to follow

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From 06c2dfc05ebf63838350a7d2571a2cdf56fcd008 Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Sat, 27 Feb 2016 19:31:01 -0500
Subject: should_follow_link(): validate ->d_seq after having decided to follow

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 at zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.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