Patch "ceph: clean up unsafe d_parent accesses in build_dentry_path" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ceph: clean up unsafe d_parent accesses in build_dentry_path

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ceph-clean-up-unsafe-d_parent-accesses-in-build_dentry_path.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jeff Layton <[email protected]>
Date: Thu, 15 Dec 2016 08:37:57 -0500
Subject: ceph: clean up unsafe d_parent accesses in build_dentry_path

From: Jeff Layton <[email protected]>

[ Upstream commit c6b0b656ca24ede6657abb4a2cd910fa9c1879ba ]

While we hold a reference to the dentry when build_dentry_path is called, we could end up racing with a rename that changes d_parent. Handle that situation correctly, by using the rcu_read_lock to ensure that the parent dentry and inode stick around long enough to safely check ceph_snap and ceph_ino.

---
 fs/ceph/mds_client.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -1782,13 +1782,18 @@ static int build_dentry_path(struct dent
 			     int *pfreepath)
 {
 	char *path;
+	struct inode *dir;
 
-	if (ceph_snap(d_inode(dentry->d_parent)) == CEPH_NOSNAP) {
-		*pino = ceph_ino(d_inode(dentry->d_parent));
+	rcu_read_lock();
+	dir = d_inode_rcu(dentry->d_parent);
+	if (dir && ceph_snap(dir) == CEPH_NOSNAP) {
+		*pino = ceph_ino(dir);
+		rcu_read_unlock();
 		*ppath = dentry->d_name.name;
 		*ppathlen = dentry->d_name.len;
 		return 0;
 	}
+	rcu_read_unlock();
 	path = ceph_mdsc_build_path(dentry, ppathlen, pino, 1);
 	if (IS_ERR(path))
 		return PTR_ERR(path);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ceph-fix-bogus-endianness-change-in-ceph_ioctl_set_layout.patch queue-4.9/ceph-clean-up-unsafe-d_parent-accesses-in-build_dentry_path.patch queue-4.9/ceph-don-t-update_dentry_lease-unless-we-actually-got-one.patch