[PATCH 4.0 020/148] ovl: mount read-only if workdir cant be created

Greg Kroah-Hartman
2015-06-03T12:17:58Z

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++)