ceph: clean up unsafe d_parent accesses in build_dentry_path

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.

Link: http://tracker.ceph.com/issues/18148
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 377ac34ddbb3a39f7a63dee208e11d61ad5fd8db..7c2eb28c24f644ab88038cd13ec1ee02f07b2b60 100644 (file)
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1800,13 +1800,18 @@ static int build_dentry_path(struct dentry *dentry,
                             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);