linux/fs/overlayfs/ovl_entry.h
Amir Goldstein 85fdee1eef ovl: fix regression caused by exclusive upper/work dir protection
Enforcing exclusive ownership on upper/work dirs caused a docker
regression: https://github.com/moby/moby/issues/34672.

Euan spotted the regression and pointed to the offending commit.
Vivek has brought the regression to my attention and provided this
reproducer:

Terminal 1:

  mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none
        merged/

Terminal 2:

  unshare -m

Terminal 1:

  umount merged
  mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none
        merged/
  mount: /root/overlay-testing/merged: none already mounted or mount point
         busy

To fix the regression, I replaced the error with an alarming warning.
With index feature enabled, mount does fail, but logs a suggestion to
override exclusive dir protection by disabling index.
Note that index=off mount does take the inuse locks, so a concurrent
index=off will issue the warning and a concurrent index=on mount will fail.

Documentation was updated to reflect this change.

Fixes: 2cac0c00a6 ("ovl: get exclusive ownership on upper/work dirs")
Cc: <stable@vger.kernel.org> # v4.13
Reported-by: Euan Kemp <euank@euank.com>
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2017-10-05 15:53:18 +02:00

82 lines
1.9 KiB
C

/*
*
* Copyright (C) 2011 Novell Inc.
* Copyright (C) 2016 Red Hat, Inc.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*/
struct ovl_config {
char *lowerdir;
char *upperdir;
char *workdir;
bool default_permissions;
bool redirect_dir;
bool index;
};
/* private information held for overlayfs's superblock */
struct ovl_fs {
struct vfsmount *upper_mnt;
unsigned numlower;
struct vfsmount **lower_mnt;
/* workbasedir is the path at workdir= mount option */
struct dentry *workbasedir;
/* workdir is the 'work' directory under workbasedir */
struct dentry *workdir;
/* index directory listing overlay inodes by origin file handle */
struct dentry *indexdir;
long namelen;
/* pathnames of lower and upper dirs, for show_options */
struct ovl_config config;
/* creds of process who forced instantiation of super block */
const struct cred *creator_cred;
bool tmpfile;
bool noxattr;
/* sb common to all layers */
struct super_block *same_sb;
/* Did we take the inuse lock? */
bool upperdir_locked;
bool workdir_locked;
};
/* private information held for every overlayfs dentry */
struct ovl_entry {
union {
struct {
unsigned long has_upper;
bool opaque;
};
struct rcu_head rcu;
};
unsigned numlower;
struct path lowerstack[];
};
struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
struct ovl_inode {
struct ovl_dir_cache *cache;
const char *redirect;
u64 version;
unsigned long flags;
struct inode vfs_inode;
struct dentry *__upperdentry;
struct inode *lower;
/* synchronize copy up and more */
struct mutex lock;
};
static inline struct ovl_inode *OVL_I(struct inode *inode)
{
return container_of(inode, struct ovl_inode, vfs_inode);
}
static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
{
return lockless_dereference(oi->__upperdentry);
}