fix NFS4 handling of mountpoint stat

RFC says we need to follow the chain of mounts if there's more
than one stacked on that point.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 3 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index a8587e90fd5a..bbf72d8f9fc0 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2121,9 +2121,15 @@ out_acl:
                  * and this is the root of a cross-mounted filesystem.
                  */
                 if (ignore_crossmnt == 0 &&
-                    exp->ex_path.mnt->mnt_root->d_inode == dentry->d_inode) {
-                        err = vfs_getattr(exp->ex_path.mnt->mnt_parent,
-                                exp->ex_path.mnt->mnt_mountpoint, &stat);
+                    dentry == exp->ex_path.mnt->mnt_root) {
+                        struct path path = exp->ex_path;
+                        path_get(&path);
+                        while (follow_up(&path)) {
+                                if (path.dentry != path.mnt->mnt_root)
+                                        break;
+                        }
+                        err = vfs_getattr(path.mnt, path.dentry, &stat);
+                        path_put(&path);
                         if (err)
                                 goto out_nfserr;
                 }