super.c 24.4 KB
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/*
 *
 * Copyright (C) 2011 Novell 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.
 */

#include <linux/fs.h>
#include <linux/namei.h>
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#include <linux/pagemap.h>
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#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/parser.h>
#include <linux/module.h>
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#include <linux/pagemap.h>
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#include <linux/sched.h>
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#include <linux/statfs.h>
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#include <linux/seq_file.h>
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#include "overlayfs.h"

MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Overlay filesystem");
MODULE_LICENSE("GPL");

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struct ovl_config {
	char *lowerdir;
	char *upperdir;
	char *workdir;
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	bool default_permissions;
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};

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/* private information held for overlayfs's superblock */
struct ovl_fs {
	struct vfsmount *upper_mnt;
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	unsigned numlower;
	struct vfsmount **lower_mnt;
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	struct dentry *workdir;
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	long lower_namelen;
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	/* pathnames of lower and upper dirs, for show_options */
	struct ovl_config config;
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};

struct ovl_dir_cache;

/* private information held for every overlayfs dentry */
struct ovl_entry {
	struct dentry *__upperdentry;
	struct ovl_dir_cache *cache;
	union {
		struct {
			u64 version;
			bool opaque;
		};
		struct rcu_head rcu;
	};
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	unsigned numlower;
	struct path lowerstack[];
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};

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#define OVL_MAX_STACK 500

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static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
{
	return oe->numlower ? oe->lowerstack[0].dentry : NULL;
}
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enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
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	enum ovl_path_type type = 0;
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	if (oe->__upperdentry) {
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		type = __OVL_PATH_UPPER;

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		if (oe->numlower) {
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			if (S_ISDIR(dentry->d_inode->i_mode))
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				type |= __OVL_PATH_MERGE;
		} else if (!oe->opaque) {
			type |= __OVL_PATH_PURE;
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		}
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	} else {
		if (oe->numlower > 1)
			type |= __OVL_PATH_MERGE;
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	}
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	return type;
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}

static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
{
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	return lockless_dereference(oe->__upperdentry);
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}

void ovl_path_upper(struct dentry *dentry, struct path *path)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct ovl_entry *oe = dentry->d_fsdata;

	path->mnt = ofs->upper_mnt;
	path->dentry = ovl_upperdentry_dereference(oe);
}

enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
{
	enum ovl_path_type type = ovl_path_type(dentry);

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	if (!OVL_TYPE_UPPER(type))
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		ovl_path_lower(dentry, path);
	else
		ovl_path_upper(dentry, path);

	return type;
}

struct dentry *ovl_dentry_upper(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	return ovl_upperdentry_dereference(oe);
}

struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

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	return __ovl_dentry_lower(oe);
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}

struct dentry *ovl_dentry_real(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	struct dentry *realdentry;

	realdentry = ovl_upperdentry_dereference(oe);
	if (!realdentry)
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		realdentry = __ovl_dentry_lower(oe);
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	return realdentry;
}

struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
{
	struct dentry *realdentry;

	realdentry = ovl_upperdentry_dereference(oe);
	if (realdentry) {
		*is_upper = true;
	} else {
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		realdentry = __ovl_dentry_lower(oe);
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		*is_upper = false;
	}
	return realdentry;
}

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struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
				    bool is_upper)
{
	if (is_upper) {
		struct ovl_fs *ofs = inode->i_sb->s_fs_info;

		return ofs->upper_mnt;
	} else {
		return oe->numlower ? oe->lowerstack[0].mnt : NULL;
	}
}

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struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	return oe->cache;
}

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bool ovl_is_default_permissions(struct inode *inode)
{
	struct ovl_fs *ofs = inode->i_sb->s_fs_info;

	return ofs->config.default_permissions;
}

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void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	oe->cache = cache;
}

void ovl_path_lower(struct dentry *dentry, struct path *path)
{
	struct ovl_entry *oe = dentry->d_fsdata;

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	*path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
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}

int ovl_want_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	return mnt_want_write(ofs->upper_mnt);
}

void ovl_drop_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	mnt_drop_write(ofs->upper_mnt);
}

struct dentry *ovl_workdir(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	return ofs->workdir;
}

bool ovl_dentry_is_opaque(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	return oe->opaque;
}

void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	oe->opaque = opaque;
}

void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
	WARN_ON(oe->__upperdentry);
	BUG_ON(!upperdentry->d_inode);
	/*
	 * Make sure upperdentry is consistent before making it visible to
	 * ovl_upperdentry_dereference().
	 */
	smp_wmb();
	oe->__upperdentry = upperdentry;
}

void ovl_dentry_version_inc(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
	oe->version++;
}

u64 ovl_dentry_version_get(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
	return oe->version;
}

bool ovl_is_whiteout(struct dentry *dentry)
{
	struct inode *inode = dentry->d_inode;

	return inode && IS_WHITEOUT(inode);
}

static bool ovl_is_opaquedir(struct dentry *dentry)
{
	int res;
	char val;
	struct inode *inode = dentry->d_inode;

	if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
		return false;

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	res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
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	if (res == 1 && val == 'y')
		return true;

	return false;
}

static void ovl_dentry_release(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	if (oe) {
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		unsigned int i;

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		dput(oe->__upperdentry);
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		for (i = 0; i < oe->numlower; i++)
			dput(oe->lowerstack[i].dentry);
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		kfree_rcu(oe, rcu);
	}
}

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static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	unsigned int i;
	int ret = 1;

	for (i = 0; i < oe->numlower; i++) {
		struct dentry *d = oe->lowerstack[i].dentry;

		if (d->d_flags & DCACHE_OP_REVALIDATE) {
			ret = d->d_op->d_revalidate(d, flags);
			if (ret < 0)
				return ret;
			if (!ret) {
				if (!(flags & LOOKUP_RCU))
					d_invalidate(d);
				return -ESTALE;
			}
		}
	}
	return 1;
}

static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	unsigned int i;
	int ret = 1;

	for (i = 0; i < oe->numlower; i++) {
		struct dentry *d = oe->lowerstack[i].dentry;

		if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
			ret = d->d_op->d_weak_revalidate(d, flags);
			if (ret <= 0)
				break;
		}
	}
	return ret;
}

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static const struct dentry_operations ovl_dentry_operations = {
	.d_release = ovl_dentry_release,
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	.d_select_inode = ovl_d_select_inode,
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};

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static const struct dentry_operations ovl_reval_dentry_operations = {
	.d_release = ovl_dentry_release,
	.d_revalidate = ovl_dentry_revalidate,
	.d_weak_revalidate = ovl_dentry_weak_revalidate,
};

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static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
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{
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	size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
	struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);

	if (oe)
		oe->numlower = numlower;

	return oe;
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}

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static bool ovl_dentry_remote(struct dentry *dentry)
{
	return dentry->d_flags &
		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
}

static bool ovl_dentry_weird(struct dentry *dentry)
{
	return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
				  DCACHE_MANAGE_TRANSIT |
				  DCACHE_OP_HASH |
				  DCACHE_OP_COMPARE);
}

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static inline struct dentry *ovl_lookup_real(struct dentry *dir,
					     struct qstr *name)
{
	struct dentry *dentry;

	mutex_lock(&dir->d_inode->i_mutex);
	dentry = lookup_one_len(name->name, dir, name->len);
	mutex_unlock(&dir->d_inode->i_mutex);

	if (IS_ERR(dentry)) {
		if (PTR_ERR(dentry) == -ENOENT)
			dentry = NULL;
	} else if (!dentry->d_inode) {
		dput(dentry);
		dentry = NULL;
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	} else if (ovl_dentry_weird(dentry)) {
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		dput(dentry);
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		/* Don't support traversing automounts and other weirdness */
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		dentry = ERR_PTR(-EREMOTE);
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	}
	return dentry;
}

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/*
 * Returns next layer in stack starting from top.
 * Returns -1 if this is the last layer.
 */
int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	BUG_ON(idx < 0);
	if (idx == 0) {
		ovl_path_upper(dentry, path);
		if (path->dentry)
			return oe->numlower ? 1 : -1;
		idx++;
	}
	BUG_ON(idx > oe->numlower);
	*path = oe->lowerstack[idx - 1];

	return (idx < oe->numlower) ? idx + 1 : -1;
}

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struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
			  unsigned int flags)
{
	struct ovl_entry *oe;
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	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
	struct path *stack = NULL;
	struct dentry *upperdir, *upperdentry = NULL;
	unsigned int ctr = 0;
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	struct inode *inode = NULL;
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	bool upperopaque = false;
	struct dentry *this, *prev = NULL;
	unsigned int i;
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	int err;

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	upperdir = ovl_upperdentry_dereference(poe);
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	if (upperdir) {
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		this = ovl_lookup_real(upperdir, &dentry->d_name);
		err = PTR_ERR(this);
		if (IS_ERR(this))
			goto out;

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		if (this) {
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			if (unlikely(ovl_dentry_remote(this))) {
				dput(this);
				err = -EREMOTE;
				goto out;
			}
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			if (ovl_is_whiteout(this)) {
				dput(this);
				this = NULL;
				upperopaque = true;
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			} else if (poe->numlower && ovl_is_opaquedir(this)) {
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				upperopaque = true;
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			}
		}
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		upperdentry = prev = this;
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	}
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	if (!upperopaque && poe->numlower) {
		err = -ENOMEM;
		stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
		if (!stack)
			goto out_put_upper;
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	}

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	for (i = 0; !upperopaque && i < poe->numlower; i++) {
		bool opaque = false;
		struct path lowerpath = poe->lowerstack[i];

		this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
		err = PTR_ERR(this);
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		if (IS_ERR(this)) {
			/*
			 * If it's positive, then treat ENAMETOOLONG as ENOENT.
			 */
			if (err == -ENAMETOOLONG && (upperdentry || ctr))
				continue;
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			goto out_put;
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		}
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		if (!this)
			continue;
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		if (ovl_is_whiteout(this)) {
			dput(this);
			break;
		}
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		/*
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		 * Only makes sense to check opaque dir if this is not the
		 * lowermost layer.
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		 */
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		if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
			opaque = true;
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		if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
			     !S_ISDIR(this->d_inode->i_mode))) {
			/*
			 * FIXME: check for upper-opaqueness maybe better done
			 * in remove code.
			 */
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			if (prev == upperdentry)
				upperopaque = true;
			dput(this);
			break;
		}
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		/*
		 * If this is a non-directory then stop here.
		 */
		if (!S_ISDIR(this->d_inode->i_mode))
			opaque = true;

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		stack[ctr].dentry = this;
		stack[ctr].mnt = lowerpath.mnt;
		ctr++;
		prev = this;
		if (opaque)
			break;
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	}

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	oe = ovl_alloc_entry(ctr);
	err = -ENOMEM;
	if (!oe)
		goto out_put;

	if (upperdentry || ctr) {
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		struct dentry *realdentry;

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		realdentry = upperdentry ? upperdentry : stack[0].dentry;

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		err = -ENOMEM;
		inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
				      oe);
		if (!inode)
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			goto out_free_oe;
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		ovl_copyattr(realdentry->d_inode, inode);
	}

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	oe->opaque = upperopaque;
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	oe->__upperdentry = upperdentry;
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	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
	kfree(stack);
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	dentry->d_fsdata = oe;
	d_add(dentry, inode);

	return NULL;

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out_free_oe:
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	kfree(oe);
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out_put:
	for (i = 0; i < ctr; i++)
		dput(stack[i].dentry);
	kfree(stack);
out_put_upper:
	dput(upperdentry);
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out:
	return ERR_PTR(err);
}

struct file *ovl_path_open(struct path *path, int flags)
{
	return dentry_open(path, flags, current_cred());
}

static void ovl_put_super(struct super_block *sb)
{
	struct ovl_fs *ufs = sb->s_fs_info;
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	unsigned i;
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	dput(ufs->workdir);
	mntput(ufs->upper_mnt);
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	for (i = 0; i < ufs->numlower; i++)
		mntput(ufs->lower_mnt[i]);
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	kfree(ufs->lower_mnt);
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	kfree(ufs->config.lowerdir);
	kfree(ufs->config.upperdir);
	kfree(ufs->config.workdir);
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	kfree(ufs);
}

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/**
 * ovl_statfs
 * @sb: The overlayfs super block
 * @buf: The struct kstatfs to fill in with stats
 *
 * Get the filesystem statistics.  As writes always target the upper layer
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 * filesystem pass the statfs to the upper filesystem (if it exists)
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 */
static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct dentry *root_dentry = dentry->d_sb->s_root;
	struct path path;
	int err;

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	ovl_path_real(root_dentry, &path);
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	err = vfs_statfs(&path, buf);
	if (!err) {
		buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
		buf->f_type = OVERLAYFS_SUPER_MAGIC;
	}

	return err;
}

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Erez Zadok 已提交
601 602 603 604 605 606 607 608 609 610 611
/**
 * ovl_show_options
 *
 * Prints the mount options for a given superblock.
 * Returns zero; does not fail.
 */
static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
{
	struct super_block *sb = dentry->d_sb;
	struct ovl_fs *ufs = sb->s_fs_info;

612
	seq_show_option(m, "lowerdir", ufs->config.lowerdir);
M
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613
	if (ufs->config.upperdir) {
614 615
		seq_show_option(m, "upperdir", ufs->config.upperdir);
		seq_show_option(m, "workdir", ufs->config.workdir);
M
Miklos Szeredi 已提交
616
	}
M
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617 618
	if (ufs->config.default_permissions)
		seq_puts(m, ",default_permissions");
E
Erez Zadok 已提交
619 620 621
	return 0;
}

622 623 624 625
static int ovl_remount(struct super_block *sb, int *flags, char *data)
{
	struct ovl_fs *ufs = sb->s_fs_info;

626
	if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
627 628 629 630 631
		return -EROFS;

	return 0;
}

M
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632 633
static const struct super_operations ovl_super_operations = {
	.put_super	= ovl_put_super,
A
Andy Whitcroft 已提交
634
	.statfs		= ovl_statfs,
E
Erez Zadok 已提交
635
	.show_options	= ovl_show_options,
636
	.remount_fs	= ovl_remount,
M
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637 638 639 640 641 642
};

enum {
	OPT_LOWERDIR,
	OPT_UPPERDIR,
	OPT_WORKDIR,
M
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643
	OPT_DEFAULT_PERMISSIONS,
M
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644 645 646 647 648 649 650
	OPT_ERR,
};

static const match_table_t ovl_tokens = {
	{OPT_LOWERDIR,			"lowerdir=%s"},
	{OPT_UPPERDIR,			"upperdir=%s"},
	{OPT_WORKDIR,			"workdir=%s"},
M
Miklos Szeredi 已提交
651
	{OPT_DEFAULT_PERMISSIONS,	"default_permissions"},
M
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652 653 654
	{OPT_ERR,			NULL}
};

M
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655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677
static char *ovl_next_opt(char **s)
{
	char *sbegin = *s;
	char *p;

	if (sbegin == NULL)
		return NULL;

	for (p = sbegin; *p; p++) {
		if (*p == '\\') {
			p++;
			if (!*p)
				break;
		} else if (*p == ',') {
			*p = '\0';
			*s = p + 1;
			return sbegin;
		}
	}
	*s = NULL;
	return sbegin;
}

M
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678 679 680 681
static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
	char *p;

M
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682
	while ((p = ovl_next_opt(&opt)) != NULL) {
M
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683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711
		int token;
		substring_t args[MAX_OPT_ARGS];

		if (!*p)
			continue;

		token = match_token(p, ovl_tokens, args);
		switch (token) {
		case OPT_UPPERDIR:
			kfree(config->upperdir);
			config->upperdir = match_strdup(&args[0]);
			if (!config->upperdir)
				return -ENOMEM;
			break;

		case OPT_LOWERDIR:
			kfree(config->lowerdir);
			config->lowerdir = match_strdup(&args[0]);
			if (!config->lowerdir)
				return -ENOMEM;
			break;

		case OPT_WORKDIR:
			kfree(config->workdir);
			config->workdir = match_strdup(&args[0]);
			if (!config->workdir)
				return -ENOMEM;
			break;

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712 713 714 715
		case OPT_DEFAULT_PERMISSIONS:
			config->default_permissions = true;
			break;

M
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716
		default:
717
			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
M
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718 719 720
			return -EINVAL;
		}
	}
H
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721 722 723 724 725 726 727 728 729

	/* Workdir is useless in non-upper mount */
	if (!config->upperdir && config->workdir) {
		pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
			config->workdir);
		kfree(config->workdir);
		config->workdir = NULL;
	}

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730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783
	return 0;
}

#define OVL_WORKDIR_NAME "work"

static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
					 struct dentry *dentry)
{
	struct inode *dir = dentry->d_inode;
	struct dentry *work;
	int err;
	bool retried = false;

	err = mnt_want_write(mnt);
	if (err)
		return ERR_PTR(err);

	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
retry:
	work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
			      strlen(OVL_WORKDIR_NAME));

	if (!IS_ERR(work)) {
		struct kstat stat = {
			.mode = S_IFDIR | 0,
		};

		if (work->d_inode) {
			err = -EEXIST;
			if (retried)
				goto out_dput;

			retried = true;
			ovl_cleanup(dir, work);
			dput(work);
			goto retry;
		}

		err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
		if (err)
			goto out_dput;
	}
out_unlock:
	mutex_unlock(&dir->i_mutex);
	mnt_drop_write(mnt);

	return work;

out_dput:
	dput(work);
	work = ERR_PTR(err);
	goto out_unlock;
}

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784 785 786 787 788 789 790 791 792 793 794 795 796
static void ovl_unescape(char *s)
{
	char *d = s;

	for (;; s++, d++) {
		if (*s == '\\')
			s++;
		*d = *s;
		if (!*s)
			break;
	}
}

M
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797 798
static int ovl_mount_dir_noesc(const char *name, struct path *path)
{
799
	int err = -EINVAL;
M
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800

801 802 803 804
	if (!*name) {
		pr_err("overlayfs: empty lowerdir\n");
		goto out;
	}
M
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805 806 807 808 809 810
	err = kern_path(name, LOOKUP_FOLLOW, path);
	if (err) {
		pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
		goto out;
	}
	err = -EINVAL;
811
	if (ovl_dentry_weird(path->dentry)) {
M
Miklos Szeredi 已提交
812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834
		pr_err("overlayfs: filesystem on '%s' not supported\n", name);
		goto out_put;
	}
	if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
		pr_err("overlayfs: '%s' not a directory\n", name);
		goto out_put;
	}
	return 0;

out_put:
	path_put(path);
out:
	return err;
}

static int ovl_mount_dir(const char *name, struct path *path)
{
	int err = -ENOMEM;
	char *tmp = kstrdup(name, GFP_KERNEL);

	if (tmp) {
		ovl_unescape(tmp);
		err = ovl_mount_dir_noesc(tmp, path);
835 836 837 838 839 840 841 842

		if (!err)
			if (ovl_dentry_remote(path->dentry)) {
				pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
				       tmp);
				path_put(path);
				err = -EINVAL;
			}
M
Miklos Szeredi 已提交
843 844 845 846 847 848
		kfree(tmp);
	}
	return err;
}

static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
849
			 int *stack_depth, bool *remote)
M
Miklos Szeredi 已提交
850 851 852 853
{
	int err;
	struct kstatfs statfs;

854
	err = ovl_mount_dir_noesc(name, path);
M
Miklos Szeredi 已提交
855 856 857 858 859 860 861 862 863 864 865
	if (err)
		goto out;

	err = vfs_statfs(path, &statfs);
	if (err) {
		pr_err("overlayfs: statfs failed on '%s'\n", name);
		goto out_put;
	}
	*namelen = max(*namelen, statfs.f_namelen);
	*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);

866 867 868
	if (ovl_dentry_remote(path->dentry))
		*remote = true;

M
Miklos Szeredi 已提交
869 870 871 872 873 874 875 876
	return 0;

out_put:
	path_put(path);
out:
	return err;
}

M
Miklos Szeredi 已提交
877 878 879 880 881 882 883 884 885 886 887 888
/* Workdir should not be subdir of upperdir and vice versa */
static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
{
	bool ok = false;

	if (workdir != upperdir) {
		ok = (lock_rename(workdir, upperdir) == NULL);
		unlock_rename(workdir, upperdir);
	}
	return ok;
}

889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908
static unsigned int ovl_split_lowerdirs(char *str)
{
	unsigned int ctr = 1;
	char *s, *d;

	for (s = d = str;; s++, d++) {
		if (*s == '\\') {
			s++;
		} else if (*s == ':') {
			*d = '\0';
			ctr++;
			continue;
		}
		*d = *s;
		if (!*s)
			break;
	}
	return ctr;
}

M
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909 910
static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
M
Miklos Szeredi 已提交
911 912
	struct path upperpath = { NULL, NULL };
	struct path workpath = { NULL, NULL };
M
Miklos Szeredi 已提交
913 914 915
	struct dentry *root_dentry;
	struct ovl_entry *oe;
	struct ovl_fs *ufs;
916 917 918 919 920
	struct path *stack = NULL;
	char *lowertmp;
	char *lower;
	unsigned int numlower;
	unsigned int stacklen = 0;
921
	unsigned int i;
922
	bool remote = false;
M
Miklos Szeredi 已提交
923 924
	int err;

E
Erez Zadok 已提交
925 926 927
	err = -ENOMEM;
	ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
	if (!ufs)
M
Miklos Szeredi 已提交
928 929
		goto out;

E
Erez Zadok 已提交
930 931 932 933
	err = ovl_parse_opt((char *) data, &ufs->config);
	if (err)
		goto out_free_config;

M
Miklos Szeredi 已提交
934
	err = -EINVAL;
M
Miklos Szeredi 已提交
935 936
	if (!ufs->config.lowerdir) {
		pr_err("overlayfs: missing 'lowerdir'\n");
M
Miklos Szeredi 已提交
937 938 939
		goto out_free_config;
	}

M
Miklos Szeredi 已提交
940
	sb->s_stack_depth = 0;
941
	sb->s_maxbytes = MAX_LFS_FILESIZE;
M
Miklos Szeredi 已提交
942 943 944 945 946
	if (ufs->config.upperdir) {
		if (!ufs->config.workdir) {
			pr_err("overlayfs: missing 'workdir'\n");
			goto out_free_config;
		}
M
Miklos Szeredi 已提交
947

M
Miklos Szeredi 已提交
948 949 950
		err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
		if (err)
			goto out_free_config;
M
Miklos Szeredi 已提交
951

H
hujianyang 已提交
952 953 954 955 956 957 958
		/* Upper fs should not be r/o */
		if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
			pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
			err = -EINVAL;
			goto out_put_upperpath;
		}

M
Miklos Szeredi 已提交
959 960 961 962
		err = ovl_mount_dir(ufs->config.workdir, &workpath);
		if (err)
			goto out_put_upperpath;

963
		err = -EINVAL;
M
Miklos Szeredi 已提交
964 965 966 967 968 969 970 971 972
		if (upperpath.mnt != workpath.mnt) {
			pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
			goto out_put_workpath;
		}
		if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
			pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
			goto out_put_workpath;
		}
		sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
A
Andy Whitcroft 已提交
973
	}
974 975 976
	err = -ENOMEM;
	lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
	if (!lowertmp)
M
Miklos Szeredi 已提交
977
		goto out_put_workpath;
978

979 980
	err = -EINVAL;
	stacklen = ovl_split_lowerdirs(lowertmp);
981 982 983
	if (stacklen > OVL_MAX_STACK) {
		pr_err("overlayfs: too many lower directries, limit is %d\n",
		       OVL_MAX_STACK);
984
		goto out_free_lowertmp;
985 986 987 988
	} else if (!ufs->config.upperdir && stacklen == 1) {
		pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
		goto out_free_lowertmp;
	}
989 990 991 992 993 994 995 996

	stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
	if (!stack)
		goto out_free_lowertmp;

	lower = lowertmp;
	for (numlower = 0; numlower < stacklen; numlower++) {
		err = ovl_lower_dir(lower, &stack[numlower],
997 998
				    &ufs->lower_namelen, &sb->s_stack_depth,
				    &remote);
999 1000 1001 1002 1003 1004
		if (err)
			goto out_put_lowerpath;

		lower = strchr(lower, '\0') + 1;
	}

1005
	err = -EINVAL;
M
Miklos Szeredi 已提交
1006
	sb->s_stack_depth++;
1007 1008
	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
		pr_err("overlayfs: maximum fs stacking depth exceeded\n");
1009
		goto out_put_lowerpath;
1010 1011
	}

M
Miklos Szeredi 已提交
1012 1013 1014 1015 1016 1017 1018
	if (ufs->config.upperdir) {
		ufs->upper_mnt = clone_private_mount(&upperpath);
		err = PTR_ERR(ufs->upper_mnt);
		if (IS_ERR(ufs->upper_mnt)) {
			pr_err("overlayfs: failed to clone upperpath\n");
			goto out_put_lowerpath;
		}
1019

M
Miklos Szeredi 已提交
1020 1021 1022
		ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
		err = PTR_ERR(ufs->workdir);
		if (IS_ERR(ufs->workdir)) {
1023 1024 1025 1026
			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;
M
Miklos Szeredi 已提交
1027
		}
M
Miklos Szeredi 已提交
1028 1029
	}

1030
	err = -ENOMEM;
1031
	ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
1032
	if (ufs->lower_mnt == NULL)
1033
		goto out_put_workdir;
1034 1035
	for (i = 0; i < numlower; i++) {
		struct vfsmount *mnt = clone_private_mount(&stack[i]);
1036

1037
		err = PTR_ERR(mnt);
1038 1039 1040 1041 1042 1043 1044 1045 1046
		if (IS_ERR(mnt)) {
			pr_err("overlayfs: failed to clone lowerpath\n");
			goto out_put_lower_mnt;
		}
		/*
		 * Make lower_mnt R/O.  That way fchmod/fchown on lower file
		 * will fail instead of modifying lower fs.
		 */
		mnt->mnt_flags |= MNT_READONLY;
1047

1048 1049 1050
		ufs->lower_mnt[ufs->numlower] = mnt;
		ufs->numlower++;
	}
M
Miklos Szeredi 已提交
1051

H
hujianyang 已提交
1052 1053
	/* If the upper fs is nonexistent, we mark overlayfs r/o too */
	if (!ufs->upper_mnt)
M
Miklos Szeredi 已提交
1054 1055
		sb->s_flags |= MS_RDONLY;

1056 1057 1058 1059
	if (remote)
		sb->s_d_op = &ovl_reval_dentry_operations;
	else
		sb->s_d_op = &ovl_dentry_operations;
M
Miklos Szeredi 已提交
1060 1061

	err = -ENOMEM;
1062
	oe = ovl_alloc_entry(numlower);
1063 1064
	if (!oe)
		goto out_put_lower_mnt;
M
Miklos Szeredi 已提交
1065

1066
	root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
M
Miklos Szeredi 已提交
1067
	if (!root_dentry)
1068
		goto out_free_oe;
M
Miklos Szeredi 已提交
1069 1070

	mntput(upperpath.mnt);
1071 1072
	for (i = 0; i < numlower; i++)
		mntput(stack[i].mnt);
M
Miklos Szeredi 已提交
1073
	path_put(&workpath);
1074
	kfree(lowertmp);
M
Miklos Szeredi 已提交
1075 1076

	oe->__upperdentry = upperpath.dentry;
1077 1078 1079 1080
	for (i = 0; i < numlower; i++) {
		oe->lowerstack[i].dentry = stack[i].dentry;
		oe->lowerstack[i].mnt = ufs->lower_mnt[i];
	}
1081
	kfree(stack);
M
Miklos Szeredi 已提交
1082 1083 1084

	root_dentry->d_fsdata = oe;

M
Miklos Szeredi 已提交
1085 1086 1087
	ovl_copyattr(ovl_dentry_real(root_dentry)->d_inode,
		     root_dentry->d_inode);

A
Andy Whitcroft 已提交
1088
	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
M
Miklos Szeredi 已提交
1089 1090 1091 1092 1093 1094
	sb->s_op = &ovl_super_operations;
	sb->s_root = root_dentry;
	sb->s_fs_info = ufs;

	return 0;

1095 1096
out_free_oe:
	kfree(oe);
M
Miklos Szeredi 已提交
1097
out_put_lower_mnt:
1098 1099 1100
	for (i = 0; i < ufs->numlower; i++)
		mntput(ufs->lower_mnt[i]);
	kfree(ufs->lower_mnt);
1101 1102
out_put_workdir:
	dput(ufs->workdir);
M
Miklos Szeredi 已提交
1103 1104
	mntput(ufs->upper_mnt);
out_put_lowerpath:
1105 1106 1107 1108 1109
	for (i = 0; i < numlower; i++)
		path_put(&stack[i]);
	kfree(stack);
out_free_lowertmp:
	kfree(lowertmp);
1110 1111
out_put_workpath:
	path_put(&workpath);
M
Miklos Szeredi 已提交
1112 1113 1114
out_put_upperpath:
	path_put(&upperpath);
out_free_config:
E
Erez Zadok 已提交
1115 1116 1117 1118
	kfree(ufs->config.lowerdir);
	kfree(ufs->config.upperdir);
	kfree(ufs->config.workdir);
	kfree(ufs);
M
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1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130
out:
	return err;
}

static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
				const char *dev_name, void *raw_data)
{
	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
}

static struct file_system_type ovl_fs_type = {
	.owner		= THIS_MODULE,
1131
	.name		= "overlay",
M
Miklos Szeredi 已提交
1132 1133 1134
	.mount		= ovl_mount,
	.kill_sb	= kill_anon_super,
};
1135
MODULE_ALIAS_FS("overlay");
M
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1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148

static int __init ovl_init(void)
{
	return register_filesystem(&ovl_fs_type);
}

static void __exit ovl_exit(void)
{
	unregister_filesystem(&ovl_fs_type);
}

module_init(ovl_init);
module_exit(ovl_exit);