/*
* Overlayfs NFS export support.
*
* Amir Goldstein <amir73il@gmail.com>
*
* Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved.
*
* 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.
*/
#include <linux/fs.h>
#include <linux/cred.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"
/*
* We only need to encode origin if there is a chance that the same object was
* encoded pre copy up and then we need to stay consistent with the same
* encoding also after copy up. If non-pure upper is not indexed, then it was
* copied up before NFS export was enabled. In that case we don't need to worry
* about staying consistent with pre copy up encoding and we encode an upper
* file handle. Overlay root dentry is a private case of non-indexed upper.
*
* The following table summarizes the different file handle encodings used for
* different overlay object types:
*
* Object type | Encoding
* --------------------------------
* Pure upper | U
* Non-indexed upper | U
* Indexed upper | L
* Non-upper | L
*
* U = upper file handle
* L = lower file handle
*/
static bool ovl_should_encode_origin(struct dentry *dentry)
{
if (!ovl_dentry_lower(dentry))
return false;
/* Decoding a non-indexed upper from origin is not implemented */
if (ovl_dentry_upper(dentry) &&
!ovl_test_flag(OVL_INDEX, d_inode(dentry)))
return false;
return true;
}
static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
{
struct dentry *upper = ovl_dentry_upper(dentry);
struct dentry *origin = ovl_dentry_lower(dentry);
struct ovl_fh *fh = NULL;
int err;
if (!ovl_should_encode_origin(dentry))
origin = NULL;
err = -EACCES;
if (!upper || origin)
goto fail;
/* TODO: encode non pure-upper by origin */
fh = ovl_encode_fh(upper, true);
err = -EOVERFLOW;
if (fh->len > buflen)
goto fail;
memcpy(buf, (char *)fh, fh->len);
err = fh->len;
out:
kfree(fh);
return err;
fail:
pr_warn_ratelimited("overlayfs: failed to encode file handle (%pd2, err=%i, buflen=%d, len=%d, type=%d)\n",
dentry, err, buflen, fh ? (int)fh->len : 0,
fh ? fh->type : 0);
goto out;
}
static int ovl_dentry_to_fh(struct dentry *dentry, u32 *fid, int *max_len)
{
int res, len = *max_len << 2;
res = ovl_d_to_fh(dentry, (char *)fid, len);
if (res <= 0)
return FILEID_INVALID;
len = res;
/* Round up to dwords */
*max_len = (len + 3) >> 2;
return OVL_FILEID;
}
static int ovl_encode_inode_fh(struct inode *inode, u32 *fid, int *max_len,
struct inode *parent)
{
struct dentry *dentry;
int type;
/* TODO: encode connectable file handles */
if (parent)
return FILEID_INVALID;
dentry = d_find_any_alias(inode);
if (WARN_ON(!dentry))
return FILEID_INVALID;
type = ovl_dentry_to_fh(dentry, fid, max_len);
dput(dentry);
return type;
}
/*
* Find or instantiate an overlay dentry from real dentries.
*/
static struct dentry *ovl_obtain_alias(struct super_block *sb,
struct dentry *upper,
struct ovl_path *lowerpath)
{
struct inode *inode;
struct dentry *dentry;
struct ovl_entry *oe;
void *fsdata = &oe;
/* TODO: obtain non pure-upper */
if (lowerpath)
return ERR_PTR(-EIO);
inode = ovl_get_inode(sb, dget(upper), NULL, NULL, 0);
if (IS_ERR(inode)) {
dput(upper);
return ERR_CAST(inode);
}
dentry = d_find_any_alias(inode);
if (!dentry) {
dentry = d_alloc_anon(inode->i_sb);
if (!dentry)
goto nomem;
oe = ovl_alloc_entry(0);
if (!oe)
goto nomem;
dentry->d_fsdata = oe;
ovl_dentry_set_upper_alias(dentry);
}
return d_instantiate_anon(dentry, inode);
nomem:
iput(inode);
dput(dentry);
return ERR_PTR(-ENOMEM);
}
/*
* Lookup a child overlay dentry to get a connected overlay dentry whose real
* dentry is @real. If @real is on upper layer, we lookup a child overlay
* dentry with the same name as the real dentry. Otherwise, we need to consult
* index for lookup.
*/
static struct dentry *ovl_lookup_real_one(struct dentry *connected,
struct dentry *real,
struct ovl_layer *layer)
{
struct inode *dir = d_inode(connected);
struct dentry *this, *parent = NULL;
struct name_snapshot name;
int err;
/* TODO: lookup by lower real dentry */
if (layer->idx)
return ERR_PTR(-EACCES);
/*
* Lookup child overlay dentry by real name. The dir mutex protects us
* from racing with overlay rename. If the overlay dentry that is above
* real has already been moved to a parent that is not under the
* connected overlay dir, we return -ECHILD and restart the lookup of
* connected real path from the top.
*/
inode_lock_nested(dir, I_MUTEX_PARENT);
err = -ECHILD;
parent = dget_parent(real);
if (ovl_dentry_upper(connected) != parent)
goto fail;
/*
* We also need to take a snapshot of real dentry name to protect us
* from racing with underlying layer rename. In this case, we don't
* care about returning ESTALE, only from dereferencing a free name
* pointer because we hold no lock on the real dentry.
*/
take_dentry_name_snapshot(&name, real);
this = lookup_one_len(name.name, connected, strlen(name.name));
err = PTR_ERR(this);
if (IS_ERR(this)) {
goto fail;
} else if (!this || !this->d_inode) {
dput(this);
err = -ENOENT;
goto fail;
} else if (ovl_dentry_upper(this) != real) {
dput(this);
err = -ESTALE;
goto fail;
}
out:
release_dentry_name_snapshot(&name);
dput(parent);
inode_unlock(dir);
return this;
fail:
pr_warn_ratelimited("overlayfs: failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
real, layer->idx, connected, err);
this = ERR_PTR(err);
goto out;
}
/*
* Lookup a connected overlay dentry whose real dentry is @real.
* If @real is on upper layer, we lookup a child overlay dentry with the same
* path the real dentry. Otherwise, we need to consult index for lookup.
*/
static struct dentry *ovl_lookup_real(struct super_block *sb,
struct dentry *real,
struct ovl_layer *layer)
{
struct dentry *connected;
int err = 0;
/* TODO: use index when looking up by lower real dentry */
if (layer->idx)
return ERR_PTR(-EACCES);
connected = dget(sb->s_root);
while (!err) {
struct dentry *next, *this;
struct dentry *parent = NULL;
struct dentry *real_connected = ovl_dentry_upper(connected);
if (real_connected == real)
break;
/* Find the topmost dentry not yet connected */
next = dget(real);
for (;;) {
parent = dget_parent(next);
if (parent == real_connected)
break;
/*
* If real has been moved out of 'real_connected',
* we will not find 'real_connected' and hit the layer
* root. In that case, we need to restart connecting.
* This game can go on forever in the worst case. We
* may want to consider taking s_vfs_rename_mutex if
* this happens more than once.
*/
if (parent == layer->mnt->mnt_root) {
dput(connected);
connected = dget(sb->s_root);
break;
}
/*
* If real file has been moved out of the layer root
* directory, we will eventully hit the real fs root.
* This cannot happen by legit overlay rename, so we
* return error in that case.
*/
if (parent == next) {
err = -EXDEV;
break;
}
dput(next);
next = parent;
}
if (!err) {
this = ovl_lookup_real_one(connected, next, layer);
if (IS_ERR(this))
err = PTR_ERR(this);
/*
* Lookup of child in overlay can fail when racing with
* overlay rename of child away from 'connected' parent.
* In this case, we need to restart the lookup from the
* top, because we cannot trust that 'real_connected' is
* still an ancestor of 'real'.
*/
if (err == -ECHILD) {
this = dget(sb->s_root);
err = 0;
}
if (!err) {
dput(connected);
connected = this;
}
}
dput(parent);
dput(next);
}
if (err)
goto fail;
return connected;
fail:
pr_warn_ratelimited("overlayfs: failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
real, layer->idx, connected, err);
dput(connected);
return ERR_PTR(err);
}
/*
* Get an overlay dentry from upper/lower real dentries.
*/
static struct dentry *ovl_get_dentry(struct super_block *sb,
struct dentry *upper,
struct ovl_path *lowerpath)
{
struct ovl_fs *ofs = sb->s_fs_info;
struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
/* TODO: get non-upper dentry */
if (!upper)
return ERR_PTR(-EACCES);
/*
* Obtain a disconnected overlay dentry from a non-dir real upper
* dentry.
*/
if (!d_is_dir(upper))
return ovl_obtain_alias(sb, upper, NULL);
/* Removed empty directory? */
if ((upper->d_flags & DCACHE_DISCONNECTED) || d_unhashed(upper))
return ERR_PTR(-ENOENT);
/*
* If real upper dentry is connected and hashed, get a connected
* overlay dentry with the same path as the real upper dentry.
*/
return ovl_lookup_real(sb, upper, &upper_layer);
}
static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
struct ovl_fh *fh)
{
struct ovl_fs *ofs = sb->s_fs_info;
struct dentry *dentry;
struct dentry *upper;
if (!ofs->upper_mnt)
return ERR_PTR(-EACCES);
upper = ovl_decode_fh(fh, ofs->upper_mnt);
if (IS_ERR_OR_NULL(upper))
return upper;
dentry = ovl_get_dentry(sb, upper, NULL);
dput(upper);
return dentry;
}
static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
int fh_len, int fh_type)
{
struct dentry *dentry = NULL;
struct ovl_fh *fh = (struct ovl_fh *) fid;
int len = fh_len << 2;
unsigned int flags = 0;
int err;
err = -EINVAL;
if (fh_type != OVL_FILEID)
goto out_err;
err = ovl_check_fh_len(fh, len);
if (err)
goto out_err;
/* TODO: decode non-upper */
flags = fh->flags;
if (flags & OVL_FH_FLAG_PATH_UPPER)
dentry = ovl_upper_fh_to_d(sb, fh);
err = PTR_ERR(dentry);
if (IS_ERR(dentry) && err != -ESTALE)
goto out_err;
return dentry;
out_err:
pr_warn_ratelimited("overlayfs: failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
len, fh_type, flags, err);
return ERR_PTR(err);
}
static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid,
int fh_len, int fh_type)
{
pr_warn_ratelimited("overlayfs: connectable file handles not supported; use 'no_subtree_check' exportfs option.\n");
return ERR_PTR(-EACCES);
}
static int ovl_get_name(struct dentry *parent, char *name,
struct dentry *child)
{
/*
* ovl_fh_to_dentry() returns connected dir overlay dentries and
* ovl_fh_to_parent() is not implemented, so we should not get here.
*/
WARN_ON_ONCE(1);
return -EIO;
}
static struct dentry *ovl_get_parent(struct dentry *dentry)
{
/*
* ovl_fh_to_dentry() returns connected dir overlay dentries, so we
* should not get here.
*/
WARN_ON_ONCE(1);
return ERR_PTR(-EIO);
}
const struct export_operations ovl_export_operations = {
.encode_fh = ovl_encode_inode_fh,
.fh_to_dentry = ovl_fh_to_dentry,
.fh_to_parent = ovl_fh_to_parent,
.get_name = ovl_get_name,
.get_parent = ovl_get_parent,
};
