Patch "ovl: mount read-only if workdir can't be created" has been added to the 4.0-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ovl: mount read-only if workdir can't be created

to the 4.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ovl-mount-read-only-if-workdir-can-t-be-created.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From cc6f67bcafcb6bbbb2d1be1603dcd95125a52800 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@suse.cz>
Date: Tue, 19 May 2015 14:30:12 +0200
Subject: ovl: mount read-only if workdir can't be created

From: Miklos Szeredi <mszeredi@suse.cz>

commit cc6f67bcafcb6bbbb2d1be1603dcd95125a52800 upstream.

OpenWRT folks reported that overlayfs fails to mount if upper fs is full,
because workdir can't be created.  Wordir creation can fail for various
other reasons too.

There's no reason that the mount itself should fail, overlayfs can work
fine without a workdir, as long as the overlay isn't modified.

So mount it read-only and don't allow remounting read-write.

Add a couple of WARN_ON()s for the impossible case of workdir being used
despite being read-only.

Reported-by: Bastian Bittorf <bittorf@bluebottle.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/overlayfs/copy_up.c |    3 +++
 fs/overlayfs/dir.c     |    9 +++++++++
 fs/overlayfs/super.c   |   10 +++++-----
 3 files changed, 17 insertions(+), 5 deletions(-)

--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -299,6 +299,9 @@ int ovl_copy_up_one(struct dentry *paren
 	struct cred *override_cred;
 	char *link = NULL;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	ovl_path_upper(parent, &parentpath);
 	upperdir = parentpath.dentry;
 
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -222,6 +222,9 @@ static struct dentry *ovl_clear_empty(st
 	struct kstat stat;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return ERR_PTR(-EROFS);
+
 	err = ovl_lock_rename_workdir(workdir, upperdir);
 	if (err)
 		goto out;
@@ -322,6 +325,9 @@ static int ovl_create_over_whiteout(stru
 	struct dentry *newdentry;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	err = ovl_lock_rename_workdir(workdir, upperdir);
 	if (err)
 		goto out;
@@ -506,6 +512,9 @@ static int ovl_remove_and_whiteout(struc
 	struct dentry *opaquedir = NULL;
 	int err;
 
+	if (WARN_ON(!workdir))
+		return -EROFS;
+
 	if (is_dir) {
 		if (OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
 			opaquedir = ovl_check_empty_and_clear(dentry);
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -529,7 +529,7 @@ static int ovl_remount(struct super_bloc
 {
 	struct ovl_fs *ufs = sb->s_fs_info;
 
-	if (!(*flags & MS_RDONLY) && !ufs->upper_mnt)
+	if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
 		return -EROFS;
 
 	return 0;
@@ -925,9 +925,10 @@ static int ovl_fill_super(struct super_b
 		ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
 		err = PTR_ERR(ufs->workdir);
 		if (IS_ERR(ufs->workdir)) {
-			pr_err("overlayfs: failed to create directory %s/%s\n",
-			       ufs->config.workdir, OVL_WORKDIR_NAME);
-			goto out_put_upper_mnt;
+			pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
+				ufs->config.workdir, OVL_WORKDIR_NAME, -err);
+			sb->s_flags |= MS_RDONLY;
+			ufs->workdir = NULL;
 		}
 	}
 
@@ -997,7 +998,6 @@ out_put_lower_mnt:
 	kfree(ufs->lower_mnt);
 out_put_workdir:
 	dput(ufs->workdir);
-out_put_upper_mnt:
 	mntput(ufs->upper_mnt);
 out_put_lowerpath:
 	for (i = 0; i < numlower; i++)


Patches currently in stable-queue which might be from mszeredi@suse.cz are

queue-4.0/ovl-don-t-remove-non-empty-opaque-directory.patch
queue-4.0/ovl-mount-read-only-if-workdir-can-t-be-created.patch