From 82ee45eb000a4f569776cbf59496cb48828bdaa0 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Wed, 8 Jul 2020 16:16:13 +0300
Subject: [PATCH] ovl: fix regression with re-formatted lower squashfs
Git-commit: a888db310195400f050b89c47673f0f8babfbb41
Patch-mainline: v5.8-rc6
References: bsc#1184176

Commit 9df085f3c9a2 ("ovl: relax requirement for non null uuid of lower
fs") relaxed the requirement for non null uuid with single lower layer to
allow enabling index and nfs_export features with single lower squashfs.

Fabian reported a regression in a setup when overlay re-uses an existing
upper layer and re-formats the lower squashfs image.  Because squashfs
has no uuid, the origin xattr in upper layer are decoded from the new
lower layer where they may resolve to a wrong origin file and user may
get an ESTALE or EIO error on lookup.

To avoid the reported regression while still allowing the new features
with single lower squashfs, do not allow decoding origin with lower null
uuid unless user opted-in to one of the new features that require
following the lower inode of non-dir upper (index, xino, metacopy).

Reported-by: Fabian <godi.beat@gmx.net>
Link: https://lore.kernel.org/linux-unionfs/32532923.JtPX5UtSzP@fgdesktop/
Fixes: 9df085f3c9a2 ("ovl: relax requirement for non null uuid of lower fs")
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
[ddiss@suse.de: rebase without 07f1e59637a8e5a8bddba5da7567d46635da510f]
Reviewed-by: David Disseldorp <ddiss@suse.de>

---
 fs/overlayfs/super.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 1e4cb019defd..d6b724beb304 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1258,6 +1258,18 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
 	if (!ofs->config.nfs_export && !ofs->upper_mnt)
 		return true;
 
+	/*
+	 * We allow using single lower with null uuid for index and nfs_export
+	 * for example to support those features with single lower squashfs.
+	 * To avoid regressions in setups of overlay with re-formatted lower
+	 * squashfs, do not allow decoding origin with lower null uuid unless
+	 * user opted-in to one of the new features that require following the
+	 * lower inode of non-dir upper.
+	 */
+	if (!ofs->config.index && !ofs->config.metacopy && !ofs->config.xino &&
+	    uuid_is_null(uuid))
+		return false;
+
 	for (i = 0; i < ofs->numlowerfs; i++) {
 		/*
 		 * We use uuid to associate an overlay lower file handle with a
-- 
2.26.2