ovl: verify stored origin fh matches lower dir

When the NFS export feature is enabled, overlayfs implicitly enables the
feature "verify_lower". When the "verify_lower" feature is enabled, a
directory inode found in lower layer by name or by redirect_dir is
verified against the file handle of the copy up origin that is stored in
the upper layer.

This introduces a change of behavior for the case of lower layer
modification while overlay is offline. A lower directory created or
moved offline under an exisitng upper directory, will not be merged with
that upper directory.

The NFS export feature should not be used after copying layers, because
the new lower directory inodes would fail verification and won't be
merged with upper directories.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 11e164cb259337f9e272cec664b3ba6f51da076d..69ca8eb075193f6ab6194087d2457dc6ad1e1cfe 100644 (file)
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -737,6 +737,18 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                        }
                }
 
+               /*
+                * When "verify_lower" feature is enabled, do not merge with a
+                * lower dir that does not match a stored origin xattr.
+                */
+               if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
+                       err = ovl_verify_origin(upperdentry, this, false);
+                       if (err) {
+                               dput(this);
+                               break;
+                       }
+               }
+
                stack[ctr].dentry = this;
                stack[ctr].layer = lower.layer;
                ctr++;