[3.16.y-ckt extended stable] Patch "be careful with nd->inode in path_init() and follow_dotdot_rcu()" has been added to staging queue

[Luis Henriques]

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

    be careful with nd->inode in path_init() and follow_dotdot_rcu()

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt1.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 3ff4c0b892ef2151d9429ffbf35a101b7764af8b Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Sat, 13 Sep 2014 21:59:43 -0400
Subject: be careful with nd->inode in path_init() and follow_dotdot_rcu()

commit 4023bfc9f351a7994fb6a7d515476c320f94a574 upstream.

in the former we simply check if dentry is still valid after picking
its ->d_inode; in the latter we fetch ->d_inode in the same places
where we fetch dentry and its ->d_seq, under the same checks.

Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/namei.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index d4ca42085e1d..8a3bdeae730c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1135,6 +1135,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,

 static int follow_dotdot_rcu(struct nameidata *nd)
 {
+	struct inode *inode = nd->inode;
 	if (!nd->root.mnt)
 		set_root_rcu(nd);

@@ -1148,6 +1149,7 @@ static int follow_dotdot_rcu(struct nameidata *nd)
 			struct dentry *parent = old->d_parent;
 			unsigned seq;

+			inode = parent->d_inode;
 			seq = read_seqcount_begin(&parent->d_seq);
 			if (read_seqcount_retry(&old->d_seq, nd->seq))
 				goto failed;
@@ -1157,6 +1159,7 @@ static int follow_dotdot_rcu(struct nameidata *nd)
 		}
 		if (!follow_up_rcu(&nd->path))
 			break;
+		inode = nd->path.dentry->d_inode;
 		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
 	}
 	while (d_mountpoint(nd->path.dentry)) {
@@ -1166,11 +1169,12 @@ static int follow_dotdot_rcu(struct nameidata *nd)
 			break;
 		nd->path.mnt = &mounted->mnt;
 		nd->path.dentry = mounted->mnt.mnt_root;
+		inode = nd->path.dentry->d_inode;
 		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
 		if (!read_seqretry(&mount_lock, nd->m_seq))
 			goto failed;
 	}
-	nd->inode = nd->path.dentry->d_inode;
+	nd->inode = inode;
 	return 0;

 failed:
@@ -1899,7 +1903,14 @@ static int path_init(int dfd, const char *name, unsigned int flags,
 	}

 	nd->inode = nd->path.dentry->d_inode;
-	return 0;
+	if (!(flags & LOOKUP_RCU))
+		return 0;
+	if (likely(!read_seqcount_retry(&nd->path.dentry->d_seq, nd->seq)))
+		return 0;
+	if (!(nd->flags & LOOKUP_ROOT))
+		nd->root.mnt = NULL;
+	rcu_read_unlock();
+	return -ECHILD;
 }

 static inline int lookup_last(struct nameidata *nd, struct path *path)
--
2.1.0