1 files changed, 30 insertions, 2 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 30adc9d408a0..22ffb23ea44d 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1175,9 +1175,29 @@ out:
 	return err;
 }
 
+static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
+{
+	unsigned int i;
+
+	if (!ofs->config.nfs_export && !(ofs->config.index && ofs->upper_mnt))
+		return true;
+
+	for (i = 0; i < ofs->numlowerfs; i++) {
+		/*
+		 * We use uuid to associate an overlay lower file handle with a
+		 * lower layer, so we can accept lower fs with null uuid as long
+		 * as all lower layers with null uuid are on the same fs.
+		 */
+		if (uuid_equal(&ofs->lower_fs[i].sb->s_uuid, uuid))
+			return false;
+	}
+	return true;
+}
+
 /* Get a unique fsid for the layer */
-static int ovl_get_fsid(struct ovl_fs *ofs, struct super_block *sb)
+static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 {
+	struct super_block *sb = path->mnt->mnt_sb;
 	unsigned int i;
 	dev_t dev;
 	int err;
@@ -1191,6 +1211,14 @@ static int ovl_get_fsid(struct ovl_fs *ofs, struct super_block *sb)
 			return i + 1;
 	}
 
+	if (!ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
+		ofs->config.index = false;
+		ofs->config.nfs_export = false;
+		pr_warn("overlayfs: %s uuid detected in lower fs '%pd2', falling back to index=off,nfs_export=off.\n",
+			uuid_is_null(&sb->s_uuid) ? "null" : "conflicting",
+			path->dentry);
+	}
+
 	err = get_anon_bdev(&dev);
 	if (err) {
 		pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
@@ -1225,7 +1253,7 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 		struct vfsmount *mnt;
 		int fsid;
 
-		err = fsid = ovl_get_fsid(ofs, stack[i].mnt->mnt_sb);
+		err = fsid = ovl_get_fsid(ofs, &stack[i]);
 		if (err < 0)
 			goto out;