[mirror_ubuntu-zesty-kernel.git] / fs / overlayfs / super.c

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

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

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

/* private information held for overlayfs's superblock */
struct ovl_fs {
        struct vfsmount *upper_mnt;
        unsigned numlower;
        struct vfsmount **lower_mnt;
        struct dentry *workdir;
        long lower_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;
};

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;
        };
        unsigned numlower;
        struct path lowerstack[];
};

#define OVL_MAX_STACK 500

static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
{
        return oe->numlower ? oe->lowerstack[0].dentry : NULL;
}

enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
        struct ovl_entry *oe = dentry->d_fsdata;
        enum ovl_path_type type = 0;

        if (oe->__upperdentry) {
                type = __OVL_PATH_UPPER;

                /*
                 * Non-dir dentry can hold lower dentry from previous
                 * location. Its purity depends only on opaque flag.
                 */
                if (oe->numlower && S_ISDIR(dentry->d_inode->i_mode))
                        type |= __OVL_PATH_MERGE;
                else if (!oe->opaque)
                        type |= __OVL_PATH_PURE;
        } else {
                if (oe->numlower > 1)
                        type |= __OVL_PATH_MERGE;
        }
        return type;
}

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

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);

        if (!OVL_TYPE_UPPER(type))
                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;

        return __ovl_dentry_lower(oe);
}

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)
                realdentry = __ovl_dentry_lower(oe);

        return realdentry;
}

static void ovl_inode_init(struct inode *inode, struct inode *realinode,
                           bool is_upper)
{
        WRITE_ONCE(inode->i_private, (unsigned long) realinode |
                   (is_upper ? OVL_ISUPPER_MASK : 0));
}

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;
        }
}

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

        return oe->cache;
}

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;

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

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

void ovl_inode_update(struct inode *inode, struct inode *upperinode)
{
        WARN_ON(!upperinode);
        WARN_ON(!inode_unhashed(inode));
        WRITE_ONCE(inode->i_private,
                   (unsigned long) upperinode | OVL_ISUPPER_MASK);
        if (!S_ISDIR(upperinode->i_mode))
                __insert_inode_hash(inode, (unsigned long) upperinode);
}

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

        WARN_ON(!inode_is_locked(dentry->d_inode));
        oe->version++;
}

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

        WARN_ON(!inode_is_locked(dentry->d_inode));
        return oe->version;
}

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

        return inode && IS_WHITEOUT(inode);
}

const struct cred *ovl_override_creds(struct super_block *sb)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        return override_creds(ofs->creator_cred);
}

static bool ovl_is_opaquedir(struct dentry *dentry)
{
        int res;
        char val;

        if (!d_is_dir(dentry))
                return false;

        res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
        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) {
                unsigned int i;

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

static struct dentry *ovl_d_real(struct dentry *dentry,
                                 const struct inode *inode,
                                 unsigned int open_flags)
{
        struct dentry *real;

        if (d_is_dir(dentry)) {
                if (!inode || inode == d_inode(dentry))
                        return dentry;
                goto bug;
        }

        if (d_is_negative(dentry))
                return dentry;

        if (open_flags) {
                int err = ovl_open_maybe_copy_up(dentry, open_flags);

                if (err)
                        return ERR_PTR(err);
        }

        real = ovl_dentry_upper(dentry);
        if (real && (!inode || inode == d_inode(real)))
                return real;

        real = ovl_dentry_lower(dentry);
        if (!real)
                goto bug;

        if (!inode || inode == d_inode(real))
                return real;

        /* Handle recursion */
        return d_real(real, inode, open_flags);
bug:
        WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
             inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
        return dentry;
}

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;
}

static const struct dentry_operations ovl_dentry_operations = {
        .d_release = ovl_dentry_release,
        .d_real = ovl_d_real,
};

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

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

        if (oe)
                oe->numlower = numlower;

        return oe;
}

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

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

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

        dentry = lookup_one_len_unlocked(name->name, dir, name->len);

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

/*
 * 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;
}

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

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

                if (this) {
                        if (unlikely(ovl_dentry_remote(this))) {
                                dput(this);
                                err = -EREMOTE;
                                goto out;
                        }
                        if (ovl_is_whiteout(this)) {
                                dput(this);
                                this = NULL;
                                upperopaque = true;
                        } else if (poe->numlower && ovl_is_opaquedir(this)) {
                                upperopaque = true;
                        }
                }
                upperdentry = prev = this;
        }

        if (!upperopaque && poe->numlower) {
                err = -ENOMEM;
                stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
                if (!stack)
                        goto out_put_upper;
        }

        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);
                if (IS_ERR(this)) {
                        /*
                         * If it's positive, then treat ENAMETOOLONG as ENOENT.
                         */
                        if (err == -ENAMETOOLONG && (upperdentry || ctr))
                                continue;
                        goto out_put;
                }
                if (!this)
                        continue;
                if (ovl_is_whiteout(this)) {
                        dput(this);
                        break;
                }
                /*
                 * Only makes sense to check opaque dir if this is not the
                 * lowermost layer.
                 */
                if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
                        opaque = true;

                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.
                         */
                        if (prev == upperdentry)
                                upperopaque = true;
                        dput(this);
                        break;
                }
                /*
                 * If this is a non-directory then stop here.
                 */
                if (!S_ISDIR(this->d_inode->i_mode))
                        opaque = true;

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

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

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

                realdentry = upperdentry ? upperdentry : stack[0].dentry;
                realinode = d_inode(realdentry);

                err = -ENOMEM;
                if (upperdentry && !d_is_dir(upperdentry)) {
                        inode = ovl_get_inode(dentry->d_sb, realinode);
                } else {
                        inode = ovl_new_inode(dentry->d_sb, realinode->i_mode);
                        if (inode)
                                ovl_inode_init(inode, realinode, !!upperdentry);
                }
                if (!inode)
                        goto out_free_oe;
                ovl_copyattr(realdentry->d_inode, inode);
        }

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

        return NULL;

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

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

static void ovl_put_super(struct super_block *sb)
{
        struct ovl_fs *ufs = sb->s_fs_info;
        unsigned i;

        dput(ufs->workdir);
        mntput(ufs->upper_mnt);
        for (i = 0; i < ufs->numlower; i++)
                mntput(ufs->lower_mnt[i]);
        kfree(ufs->lower_mnt);

        kfree(ufs->config.lowerdir);
        kfree(ufs->config.upperdir);
        kfree(ufs->config.workdir);
        put_cred(ufs->creator_cred);
        kfree(ufs);
}

/**
 * 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
 * filesystem pass the statfs to the upper filesystem (if it exists)
 */
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;

        ovl_path_real(root_dentry, &path);

        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;
}

/**
 * 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;

        seq_show_option(m, "lowerdir", ufs->config.lowerdir);
        if (ufs->config.upperdir) {
                seq_show_option(m, "upperdir", ufs->config.upperdir);
                seq_show_option(m, "workdir", ufs->config.workdir);
        }
        if (ufs->config.default_permissions)
                seq_puts(m, ",default_permissions");
        return 0;
}

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

        if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
                return -EROFS;

        return 0;
}

static const struct super_operations ovl_super_operations = {
        .put_super      = ovl_put_super,
        .statfs         = ovl_statfs,
        .show_options   = ovl_show_options,
        .remount_fs     = ovl_remount,
        .drop_inode     = generic_delete_inode,
};

enum {
        OPT_LOWERDIR,
        OPT_UPPERDIR,
        OPT_WORKDIR,
        OPT_DEFAULT_PERMISSIONS,
        OPT_ERR,
};

static const match_table_t ovl_tokens = {
        {OPT_LOWERDIR,                  "lowerdir=%s"},
        {OPT_UPPERDIR,                  "upperdir=%s"},
        {OPT_WORKDIR,                   "workdir=%s"},
        {OPT_DEFAULT_PERMISSIONS,       "default_permissions"},
        {OPT_ERR,                       NULL}
};

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;
}

static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
        char *p;

        while ((p = ovl_next_opt(&opt)) != NULL) {
                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;

                case OPT_DEFAULT_PERMISSIONS:
                        config->default_permissions = true;
                        break;

                default:
                        pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
                        return -EINVAL;
                }
        }

        /* 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;
        }

        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);

        inode_lock_nested(dir, 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,
                };
                struct iattr attr = {
                        .ia_valid = ATTR_MODE,
                        .ia_mode = stat.mode,
                };

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

                        retried = true;
                        ovl_workdir_cleanup(dir, mnt, work, 0);
                        dput(work);
                        goto retry;
                }

                err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
                if (err)
                        goto out_dput;

                /*
                 * Try to remove POSIX ACL xattrs from workdir.  We are good if:
                 *
                 * a) success (there was a POSIX ACL xattr and was removed)
                 * b) -ENODATA (there was no POSIX ACL xattr)
                 * c) -EOPNOTSUPP (POSIX ACL xattrs are not supported)
                 *
                 * There are various other error values that could effectively
                 * mean that the xattr doesn't exist (e.g. -ERANGE is returned
                 * if the xattr name is too long), but the set of filesystems
                 * allowed as upper are limited to "normal" ones, where checking
                 * for the above two errors is sufficient.
                 */
                err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
                if (err && err != -ENODATA && err != -EOPNOTSUPP)
                        goto out_dput;

                err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
                if (err && err != -ENODATA && err != -EOPNOTSUPP)
                        goto out_dput;

                /* Clear any inherited mode bits */
                inode_lock(work->d_inode);
                err = notify_change(work, &attr, NULL);
                inode_unlock(work->d_inode);
                if (err)
                        goto out_dput;
        }
out_unlock:
        inode_unlock(dir);
        mnt_drop_write(mnt);

        return work;

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

static void ovl_unescape(char *s)
{
        char *d = s;

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

static int ovl_mount_dir_noesc(const char *name, struct path *path)
{
        int err = -EINVAL;

        if (!*name) {
                pr_err("overlayfs: empty lowerdir\n");
                goto out;
        }
        err = kern_path(name, LOOKUP_FOLLOW, path);
        if (err) {
                pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
                goto out;
        }
        err = -EINVAL;
        if (ovl_dentry_weird(path->dentry)) {
                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);

                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;
                        }
                kfree(tmp);
        }
        return err;
}

static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
                         int *stack_depth, bool *remote)
{
        int err;
        struct kstatfs statfs;

        err = ovl_mount_dir_noesc(name, path);
        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);

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

        return 0;

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

/* 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;
}

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;
}

static int __maybe_unused
ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
                        struct dentry *dentry, struct inode *inode,
                        const char *name, void *buffer, size_t size)
{
        return ovl_xattr_get(dentry, handler->name, buffer, size);
}

static int __maybe_unused
ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
                        struct dentry *dentry, struct inode *inode,
                        const char *name, const void *value,
                        size_t size, int flags)
{
        struct dentry *workdir = ovl_workdir(dentry);
        struct inode *realinode = ovl_inode_real(inode, NULL);
        struct posix_acl *acl = NULL;
        int err;

        /* Check that everything is OK before copy-up */
        if (value) {
                acl = posix_acl_from_xattr(&init_user_ns, value, size);
                if (IS_ERR(acl))
                        return PTR_ERR(acl);
        }
        err = -EOPNOTSUPP;
        if (!IS_POSIXACL(d_inode(workdir)))
                goto out_acl_release;
        if (!realinode->i_op->set_acl)
                goto out_acl_release;
        if (handler->flags == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode)) {
                err = acl ? -EACCES : 0;
                goto out_acl_release;
        }
        err = -EPERM;
        if (!inode_owner_or_capable(inode))
                goto out_acl_release;

        posix_acl_release(acl);

        err = ovl_xattr_set(dentry, handler->name, value, size, flags);
        if (!err)
                ovl_copyattr(ovl_inode_real(inode, NULL), inode);

        return err;

out_acl_release:
        posix_acl_release(acl);
        return err;
}

static int ovl_own_xattr_get(const struct xattr_handler *handler,
                             struct dentry *dentry, struct inode *inode,
                             const char *name, void *buffer, size_t size)
{
        return -EPERM;
}

static int ovl_own_xattr_set(const struct xattr_handler *handler,
                             struct dentry *dentry, struct inode *inode,
                             const char *name, const void *value,
                             size_t size, int flags)
{
        return -EPERM;
}

static int ovl_other_xattr_get(const struct xattr_handler *handler,
                               struct dentry *dentry, struct inode *inode,
                               const char *name, void *buffer, size_t size)
{
        return ovl_xattr_get(dentry, name, buffer, size);
}

static int ovl_other_xattr_set(const struct xattr_handler *handler,
                               struct dentry *dentry, struct inode *inode,
                               const char *name, const void *value,
                               size_t size, int flags)
{
        return ovl_xattr_set(dentry, name, value, size, flags);
}

static const struct xattr_handler __maybe_unused
ovl_posix_acl_access_xattr_handler = {
        .name = XATTR_NAME_POSIX_ACL_ACCESS,
        .flags = ACL_TYPE_ACCESS,
        .get = ovl_posix_acl_xattr_get,
        .set = ovl_posix_acl_xattr_set,
};

static const struct xattr_handler __maybe_unused
ovl_posix_acl_default_xattr_handler = {
        .name = XATTR_NAME_POSIX_ACL_DEFAULT,
        .flags = ACL_TYPE_DEFAULT,
        .get = ovl_posix_acl_xattr_get,
        .set = ovl_posix_acl_xattr_set,
};

static const struct xattr_handler ovl_own_xattr_handler = {
        .prefix = OVL_XATTR_PREFIX,
        .get = ovl_own_xattr_get,
        .set = ovl_own_xattr_set,
};

static const struct xattr_handler ovl_other_xattr_handler = {
        .prefix = "", /* catch all */
        .get = ovl_other_xattr_get,
        .set = ovl_other_xattr_set,
};

static const struct xattr_handler *ovl_xattr_handlers[] = {
#ifdef CONFIG_FS_POSIX_ACL
        &ovl_posix_acl_access_xattr_handler,
        &ovl_posix_acl_default_xattr_handler,
#endif
        &ovl_own_xattr_handler,
        &ovl_other_xattr_handler,
        NULL
};

static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
        struct path upperpath = { NULL, NULL };
        struct path workpath = { NULL, NULL };
        struct dentry *root_dentry;
        struct inode *realinode;
        struct ovl_entry *oe;
        struct ovl_fs *ufs;
        struct path *stack = NULL;
        char *lowertmp;
        char *lower;
        unsigned int numlower;
        unsigned int stacklen = 0;
        unsigned int i;
        bool remote = false;
        int err;

        err = -ENOMEM;
        ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
        if (!ufs)
                goto out;

        err = ovl_parse_opt((char *) data, &ufs->config);
        if (err)
                goto out_free_config;

        err = -EINVAL;
        if (!ufs->config.lowerdir) {
                if (!silent)
                        pr_err("overlayfs: missing 'lowerdir'\n");
                goto out_free_config;
        }

        sb->s_stack_depth = 0;
        sb->s_maxbytes = MAX_LFS_FILESIZE;
        if (ufs->config.upperdir) {
                if (!ufs->config.workdir) {
                        pr_err("overlayfs: missing 'workdir'\n");
                        goto out_free_config;
                }

                err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
                if (err)
                        goto out_free_config;

                /* 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;
                }

                err = ovl_mount_dir(ufs->config.workdir, &workpath);
                if (err)
                        goto out_put_upperpath;

                err = -EINVAL;
                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;
        }
        err = -ENOMEM;
        lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
        if (!lowertmp)
                goto out_put_workpath;

        err = -EINVAL;
        stacklen = ovl_split_lowerdirs(lowertmp);
        if (stacklen > OVL_MAX_STACK) {
                pr_err("overlayfs: too many lower directories, limit is %d\n",
                       OVL_MAX_STACK);
                goto out_free_lowertmp;
        } else if (!ufs->config.upperdir && stacklen == 1) {
                pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
                goto out_free_lowertmp;
        }

        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],
                                    &ufs->lower_namelen, &sb->s_stack_depth,
                                    &remote);
                if (err)
                        goto out_put_lowerpath;

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

        err = -EINVAL;
        sb->s_stack_depth++;
        if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
                pr_err("overlayfs: maximum fs stacking depth exceeded\n");
                goto out_put_lowerpath;
        }

        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;
                }
                /* Don't inherit atime flags */
                ufs->upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);

                sb->s_time_gran = ufs->upper_mnt->mnt_sb->s_time_gran;

                ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
                err = PTR_ERR(ufs->workdir);
                if (IS_ERR(ufs->workdir)) {
                        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;
                }

                /*
                 * Upper should support d_type, else whiteouts are visible.
                 * Given workdir and upper are on same fs, we can do
                 * iterate_dir() on workdir. This check requires successful
                 * creation of workdir in previous step.
                 */
                if (ufs->workdir) {
                        err = ovl_check_d_type_supported(&workpath);
                        if (err < 0)
                                goto out_put_workdir;

                        /*
                         * We allowed this configuration and don't want to
                         * break users over kernel upgrade. So warn instead
                         * of erroring out.
                         */
                        if (!err)
                                pr_warn("overlayfs: upper fs needs to support d_type.\n");
                }
        }

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

                err = PTR_ERR(mnt);
                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 | MNT_NOATIME;

                ufs->lower_mnt[ufs->numlower] = mnt;
                ufs->numlower++;
        }

        /* If the upper fs is nonexistent, we mark overlayfs r/o too */
        if (!ufs->upper_mnt)
                sb->s_flags |= MS_RDONLY;

        if (remote)
                sb->s_d_op = &ovl_reval_dentry_operations;
        else
                sb->s_d_op = &ovl_dentry_operations;

        ufs->creator_cred = prepare_creds();
        if (!ufs->creator_cred)
                goto out_put_lower_mnt;

        err = -ENOMEM;
        oe = ovl_alloc_entry(numlower);
        if (!oe)
                goto out_put_cred;

        root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR));
        if (!root_dentry)
                goto out_free_oe;

        mntput(upperpath.mnt);
        for (i = 0; i < numlower; i++)
                mntput(stack[i].mnt);
        path_put(&workpath);
        kfree(lowertmp);

        oe->__upperdentry = upperpath.dentry;
        for (i = 0; i < numlower; i++) {
                oe->lowerstack[i].dentry = stack[i].dentry;
                oe->lowerstack[i].mnt = ufs->lower_mnt[i];
        }
        kfree(stack);

        root_dentry->d_fsdata = oe;

        realinode = d_inode(ovl_dentry_real(root_dentry));
        ovl_inode_init(d_inode(root_dentry), realinode, !!upperpath.dentry);
        ovl_copyattr(realinode, d_inode(root_dentry));

        sb->s_magic = OVERLAYFS_SUPER_MAGIC;
        sb->s_op = &ovl_super_operations;
        sb->s_xattr = ovl_xattr_handlers;
        sb->s_root = root_dentry;
        sb->s_fs_info = ufs;
        sb->s_flags |= MS_POSIXACL;

        return 0;

out_free_oe:
        kfree(oe);
out_put_cred:
        put_cred(ufs->creator_cred);
out_put_lower_mnt:
        for (i = 0; i < ufs->numlower; i++)
                mntput(ufs->lower_mnt[i]);
        kfree(ufs->lower_mnt);
out_put_workdir:
        dput(ufs->workdir);
        mntput(ufs->upper_mnt);
out_put_lowerpath:
        for (i = 0; i < numlower; i++)
                path_put(&stack[i]);
        kfree(stack);
out_free_lowertmp:
        kfree(lowertmp);
out_put_workpath:
        path_put(&workpath);
out_put_upperpath:
        path_put(&upperpath);
out_free_config:
        kfree(ufs->config.lowerdir);
        kfree(ufs->config.upperdir);
        kfree(ufs->config.workdir);
        kfree(ufs);
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,
        .name           = "overlay",
        .mount          = ovl_mount,
        .kill_sb        = kill_anon_super,
};
MODULE_ALIAS_FS("overlay");

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);