/*
 *
 * 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/xattr.h>
#include <linux/security.h>
#include <linux/cred.h>
#include <linux/module.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
#include <linux/atomic.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

static unsigned short ovl_redirect_max = 256;
module_param_named(redirect_max, ovl_redirect_max, ushort, 0644);
MODULE_PARM_DESC(ovl_redirect_max,
                 "Maximum length of absolute redirect xattr value");

int ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
{
        int err;

        dget(wdentry);
        if (d_is_dir(wdentry))
                err = ovl_do_rmdir(wdir, wdentry);
        else
                err = ovl_do_unlink(wdir, wdentry);
        dput(wdentry);

        if (err) {
                pr_err("overlayfs: cleanup of '%pd2' failed (%i)\n",
                       wdentry, err);
        }

        return err;
}

struct dentry *ovl_lookup_temp(struct dentry *workdir)
{
        struct dentry *temp;
        char name[20];
        static atomic_t temp_id = ATOMIC_INIT(0);

        /* counter is allowed to wrap, since temp dentries are ephemeral */
        snprintf(name, sizeof(name), "#%x", atomic_inc_return(&temp_id));

        temp = lookup_one_len(name, workdir, strlen(name));
        if (!IS_ERR(temp) && temp->d_inode) {
                pr_err("overlayfs: workdir/%s already exists\n", name);
                dput(temp);
                temp = ERR_PTR(-EIO);
        }

        return temp;
}

/* caller holds i_mutex on workdir */
static struct dentry *ovl_whiteout(struct dentry *workdir,
                                   struct dentry *dentry)
{
        int err;
        struct dentry *whiteout;
        struct inode *wdir = workdir->d_inode;

        whiteout = ovl_lookup_temp(workdir);
        if (IS_ERR(whiteout))
                return whiteout;

        err = ovl_do_whiteout(wdir, whiteout);
        if (err) {
                dput(whiteout);
                whiteout = ERR_PTR(err);
        }

        return whiteout;
}

int ovl_create_real(struct inode *dir, struct dentry *newdentry,
                    struct cattr *attr, struct dentry *hardlink, bool debug)
{
        int err;

        if (newdentry->d_inode)
                return -ESTALE;

        if (hardlink) {
                err = ovl_do_link(hardlink, dir, newdentry, debug);
        } else {
                switch (attr->mode & S_IFMT) {
                case S_IFREG:
                        err = ovl_do_create(dir, newdentry, attr->mode, debug);
                        break;

                case S_IFDIR:
                        err = ovl_do_mkdir(dir, newdentry, attr->mode, debug);
                        break;

                case S_IFCHR:
                case S_IFBLK:
                case S_IFIFO:
                case S_IFSOCK:
                        err = ovl_do_mknod(dir, newdentry,
                                           attr->mode, attr->rdev, debug);
                        break;

                case S_IFLNK:
                        err = ovl_do_symlink(dir, newdentry, attr->link, debug);
                        break;

                default:
                        err = -EPERM;
                }
        }
        if (!err && WARN_ON(!newdentry->d_inode)) {
                /*
                 * Not quite sure if non-instantiated dentry is legal or not.
                 * VFS doesn't seem to care so check and warn here.
                 */
                err = -ENOENT;
        }
        return err;
}

static int ovl_set_opaque_xerr(struct dentry *dentry, struct dentry *upper,
                               int xerr)
{
        int err;

        err = ovl_check_setxattr(dentry, upper, OVL_XATTR_OPAQUE, "y", 1, xerr);
        if (!err)
                ovl_dentry_set_opaque(dentry);

        return err;
}

static int ovl_set_opaque(struct dentry *dentry, struct dentry *upperdentry)
{
        /*
         * Fail with -EIO when trying to create opaque dir and upper doesn't
         * support xattrs. ovl_rename() calls ovl_set_opaque_xerr(-EXDEV) to
         * return a specific error for noxattr case.
         */
        return ovl_set_opaque_xerr(dentry, upperdentry, -EIO);
}

/* Common operations required to be done after creation of file on upper */
static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
                            struct dentry *newdentry, bool hardlink)
{
        ovl_dentry_version_inc(dentry->d_parent);
        ovl_dentry_set_upper_alias(dentry);
        if (!hardlink) {
                ovl_inode_update(inode, newdentry);
                ovl_copyattr(newdentry->d_inode, inode);
        } else {
                WARN_ON(ovl_inode_real(inode) != d_inode(newdentry));
                dput(newdentry);
                inc_nlink(inode);
        }
        d_instantiate(dentry, inode);
        /* Force lookup of new upper hardlink to find its lower */
        if (hardlink)
                d_drop(dentry);
}

static bool ovl_type_merge(struct dentry *dentry)
{
        return OVL_TYPE_MERGE(ovl_path_type(dentry));
}

static bool ovl_type_origin(struct dentry *dentry)
{
        return OVL_TYPE_ORIGIN(ovl_path_type(dentry));
}

static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
                            struct cattr *attr, struct dentry *hardlink)
{
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *udir = upperdir->d_inode;
        struct dentry *newdentry;
        int err;

        if (!hardlink && !IS_POSIXACL(udir))
                attr->mode &= ~current_umask();

        inode_lock_nested(udir, I_MUTEX_PARENT);
        newdentry = lookup_one_len(dentry->d_name.name, upperdir,
                                   dentry->d_name.len);
        err = PTR_ERR(newdentry);
        if (IS_ERR(newdentry))
                goto out_unlock;
        err = ovl_create_real(udir, newdentry, attr, hardlink, false);
        if (err)
                goto out_dput;

        if (ovl_type_merge(dentry->d_parent) && d_is_dir(newdentry)) {
                /* Setting opaque here is just an optimization, allow to fail */
                ovl_set_opaque(dentry, newdentry);
        }

        ovl_instantiate(dentry, inode, newdentry, !!hardlink);
        newdentry = NULL;
out_dput:
        dput(newdentry);
out_unlock:
        inode_unlock(udir);
        return err;
}

static int ovl_lock_rename_workdir(struct dentry *workdir,
                                   struct dentry *upperdir)
{
        /* Workdir should not be the same as upperdir */
        if (workdir == upperdir)
                goto err;

        /* Workdir should not be subdir of upperdir and vice versa */
        if (lock_rename(workdir, upperdir) != NULL)
                goto err_unlock;

        return 0;

err_unlock:
        unlock_rename(workdir, upperdir);
err:
        pr_err("overlayfs: failed to lock workdir+upperdir\n");
        return -EIO;
}

static struct dentry *ovl_clear_empty(struct dentry *dentry,
                                      struct list_head *list)
{
        struct dentry *workdir = ovl_workdir(dentry);
        struct inode *wdir = workdir->d_inode;
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *udir = upperdir->d_inode;
        struct path upperpath;
        struct dentry *upper;
        struct dentry *opaquedir;
        struct kstat stat;
        int err;

        if (WARN_ON(!workdir))
                return ERR_PTR(-EROFS);

        err = ovl_lock_rename_workdir(workdir, upperdir);
        if (err)
                goto out;

        ovl_path_upper(dentry, &upperpath);
        err = vfs_getattr(&upperpath, &stat,
                          STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
        if (err)
                goto out_unlock;

        err = -ESTALE;
        if (!S_ISDIR(stat.mode))
                goto out_unlock;
        upper = upperpath.dentry;
        if (upper->d_parent->d_inode != udir)
                goto out_unlock;

        opaquedir = ovl_lookup_temp(workdir);
        err = PTR_ERR(opaquedir);
        if (IS_ERR(opaquedir))
                goto out_unlock;

        err = ovl_create_real(wdir, opaquedir,
                              &(struct cattr){.mode = stat.mode}, NULL, true);
        if (err)
                goto out_dput;

        err = ovl_copy_xattr(upper, opaquedir);
        if (err)
                goto out_cleanup;

        err = ovl_set_opaque(dentry, opaquedir);
        if (err)
                goto out_cleanup;

        inode_lock(opaquedir->d_inode);
        err = ovl_set_attr(opaquedir, &stat);
        inode_unlock(opaquedir->d_inode);
        if (err)
                goto out_cleanup;

        err = ovl_do_rename(wdir, opaquedir, udir, upper, RENAME_EXCHANGE);
        if (err)
                goto out_cleanup;

        ovl_cleanup_whiteouts(upper, list);
        ovl_cleanup(wdir, upper);
        unlock_rename(workdir, upperdir);

        /* dentry's upper doesn't match now, get rid of it */
        d_drop(dentry);

        return opaquedir;

out_cleanup:
        ovl_cleanup(wdir, opaquedir);
out_dput:
        dput(opaquedir);
out_unlock:
        unlock_rename(workdir, upperdir);
out:
        return ERR_PTR(err);
}

static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry)
{
        int err;
        struct dentry *ret = NULL;
        enum ovl_path_type type = ovl_path_type(dentry);
        LIST_HEAD(list);

        err = ovl_check_empty_dir(dentry, &list);
        if (err) {
                ret = ERR_PTR(err);
                goto out_free;
        }

        /*
         * When removing an empty opaque directory, then it makes no sense to
         * replace it with an exact replica of itself.
         *
         * If no upperdentry then skip clearing whiteouts.
         *
         * Can race with copy-up, since we don't hold the upperdir mutex.
         * Doesn't matter, since copy-up can't create a non-empty directory
         * from an empty one.
         */
        if (OVL_TYPE_UPPER(type) && OVL_TYPE_MERGE(type))
                ret = ovl_clear_empty(dentry, &list);

out_free:
        ovl_cache_free(&list);

        return ret;
}

static int ovl_set_upper_acl(struct dentry *upperdentry, const char *name,
                             const struct posix_acl *acl)
{
        void *buffer;
        size_t size;
        int err;

        if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !acl)
                return 0;

        size = posix_acl_to_xattr(NULL, acl, NULL, 0);
        buffer = kmalloc(size, GFP_KERNEL);
        if (!buffer)
                return -ENOMEM;

        size = posix_acl_to_xattr(&init_user_ns, acl, buffer, size);
        err = size;
        if (err < 0)
                goto out_free;

        err = vfs_setxattr(upperdentry, name, buffer, size, XATTR_CREATE);
out_free:
        kfree(buffer);
        return err;
}

static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
                                    struct cattr *cattr,
                                    struct dentry *hardlink)
{
        struct dentry *workdir = ovl_workdir(dentry);
        struct inode *wdir = workdir->d_inode;
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *udir = upperdir->d_inode;
        struct dentry *upper;
        struct dentry *newdentry;
        int err;
        struct posix_acl *acl, *default_acl;

        if (WARN_ON(!workdir))
                return -EROFS;

        if (!hardlink) {
                err = posix_acl_create(dentry->d_parent->d_inode,
                                       &cattr->mode, &default_acl, &acl);
                if (err)
                        return err;
        }

        err = ovl_lock_rename_workdir(workdir, upperdir);
        if (err)
                goto out;

        newdentry = ovl_lookup_temp(workdir);
        err = PTR_ERR(newdentry);
        if (IS_ERR(newdentry))
                goto out_unlock;

        upper = lookup_one_len(dentry->d_name.name, upperdir,
                               dentry->d_name.len);
        err = PTR_ERR(upper);
        if (IS_ERR(upper))
                goto out_dput;

        err = ovl_create_real(wdir, newdentry, cattr, hardlink, true);
        if (err)
                goto out_dput2;

        /*
         * mode could have been mutilated due to umask (e.g. sgid directory)
         */
        if (!hardlink &&
            !S_ISLNK(cattr->mode) &&
            newdentry->d_inode->i_mode != cattr->mode) {
                struct iattr attr = {
                        .ia_valid = ATTR_MODE,
                        .ia_mode = cattr->mode,
                };
                inode_lock(newdentry->d_inode);
                err = notify_change(newdentry, &attr, NULL);
                inode_unlock(newdentry->d_inode);
                if (err)
                        goto out_cleanup;
        }
        if (!hardlink) {
                err = ovl_set_upper_acl(newdentry, XATTR_NAME_POSIX_ACL_ACCESS,
                                        acl);
                if (err)
                        goto out_cleanup;

                err = ovl_set_upper_acl(newdentry, XATTR_NAME_POSIX_ACL_DEFAULT,
                                        default_acl);
                if (err)
                        goto out_cleanup;
        }

        if (!hardlink && S_ISDIR(cattr->mode)) {
                err = ovl_set_opaque(dentry, newdentry);
                if (err)
                        goto out_cleanup;

                err = ovl_do_rename(wdir, newdentry, udir, upper,
                                    RENAME_EXCHANGE);
                if (err)
                        goto out_cleanup;

                ovl_cleanup(wdir, upper);
        } else {
                err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
                if (err)
                        goto out_cleanup;
        }
        ovl_instantiate(dentry, inode, newdentry, !!hardlink);
        newdentry = NULL;
out_dput2:
        dput(upper);
out_dput:
        dput(newdentry);
out_unlock:
        unlock_rename(workdir, upperdir);
out:
        if (!hardlink) {
                posix_acl_release(acl);
                posix_acl_release(default_acl);
        }
        return err;

out_cleanup:
        ovl_cleanup(wdir, newdentry);
        goto out_dput2;
}

static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
                              struct cattr *attr, struct dentry *hardlink,
                              bool origin)
{
        int err;
        const struct cred *old_cred;
        struct cred *override_cred;
        struct dentry *parent = dentry->d_parent;

        err = ovl_copy_up(parent);
        if (err)
                return err;

        old_cred = ovl_override_creds(dentry->d_sb);

        /*
         * When linking a file with copy up origin into a new parent, mark the
         * new parent dir "impure".
         */
        if (origin) {
                err = ovl_set_impure(parent, ovl_dentry_upper(parent));
                if (err)
                        goto out_revert_creds;
        }

        err = -ENOMEM;
        override_cred = prepare_creds();
        if (override_cred) {
                override_cred->fsuid = inode->i_uid;
                override_cred->fsgid = inode->i_gid;
                if (!hardlink) {
                        err = security_dentry_create_files_as(dentry,
                                        attr->mode, &dentry->d_name, old_cred,
                                        override_cred);
                        if (err) {
                                put_cred(override_cred);
                                goto out_revert_creds;
                        }
                }
                put_cred(override_creds(override_cred));
                put_cred(override_cred);

                if (!ovl_dentry_is_whiteout(dentry))
                        err = ovl_create_upper(dentry, inode, attr,
                                                hardlink);
                else
                        err = ovl_create_over_whiteout(dentry, inode, attr,
                                                        hardlink);
        }
out_revert_creds:
        revert_creds(old_cred);
        if (!err) {
                struct inode *realinode = d_inode(ovl_dentry_upper(dentry));

                WARN_ON(inode->i_mode != realinode->i_mode);
                WARN_ON(!uid_eq(inode->i_uid, realinode->i_uid));
                WARN_ON(!gid_eq(inode->i_gid, realinode->i_gid));
        }
        return err;
}

static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
                             const char *link)
{
        int err;
        struct inode *inode;
        struct cattr attr = {
                .rdev = rdev,
                .link = link,
        };

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        err = -ENOMEM;
        inode = ovl_new_inode(dentry->d_sb, mode, rdev);
        if (!inode)
                goto out_drop_write;

        inode_init_owner(inode, dentry->d_parent->d_inode, mode);
        attr.mode = inode->i_mode;

        err = ovl_create_or_link(dentry, inode, &attr, NULL, false);
        if (err)
                iput(inode);

out_drop_write:
        ovl_drop_write(dentry);
out:
        return err;
}

static int ovl_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                      bool excl)
{
        return ovl_create_object(dentry, (mode & 07777) | S_IFREG, 0, NULL);
}

static int ovl_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        return ovl_create_object(dentry, (mode & 07777) | S_IFDIR, 0, NULL);
}

static int ovl_mknod(struct inode *dir, struct dentry *dentry, umode_t mode,
                     dev_t rdev)
{
        /* Don't allow creation of "whiteout" on overlay */
        if (S_ISCHR(mode) && rdev == WHITEOUT_DEV)
                return -EPERM;

        return ovl_create_object(dentry, mode, rdev, NULL);
}

static int ovl_symlink(struct inode *dir, struct dentry *dentry,
                       const char *link)
{
        return ovl_create_object(dentry, S_IFLNK, 0, link);
}

static int ovl_link(struct dentry *old, struct inode *newdir,
                    struct dentry *new)
{
        int err;
        bool locked = false;
        struct inode *inode;

        err = ovl_want_write(old);
        if (err)
                goto out;

        err = ovl_copy_up(old);
        if (err)
                goto out_drop_write;

        err = ovl_nlink_start(old, &locked);
        if (err)
                goto out_drop_write;

        inode = d_inode(old);
        ihold(inode);

        err = ovl_create_or_link(new, inode, NULL, ovl_dentry_upper(old),
                                 ovl_type_origin(old));
        if (err)
                iput(inode);

        ovl_nlink_end(old, locked);
out_drop_write:
        ovl_drop_write(old);
out:
        return err;
}

static bool ovl_matches_upper(struct dentry *dentry, struct dentry *upper)
{
        return d_inode(ovl_dentry_upper(dentry)) == d_inode(upper);
}

static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
{
        struct dentry *workdir = ovl_workdir(dentry);
        struct inode *wdir = workdir->d_inode;
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *udir = upperdir->d_inode;
        struct dentry *whiteout;
        struct dentry *upper;
        struct dentry *opaquedir = NULL;
        int err;
        int flags = 0;

        if (WARN_ON(!workdir))
                return -EROFS;

        if (is_dir) {
                opaquedir = ovl_check_empty_and_clear(dentry);
                err = PTR_ERR(opaquedir);
                if (IS_ERR(opaquedir))
                        goto out;
        }

        err = ovl_lock_rename_workdir(workdir, upperdir);
        if (err)
                goto out_dput;

        upper = lookup_one_len(dentry->d_name.name, upperdir,
                               dentry->d_name.len);
        err = PTR_ERR(upper);
        if (IS_ERR(upper))
                goto out_unlock;

        err = -ESTALE;
        if ((opaquedir && upper != opaquedir) ||
            (!opaquedir && ovl_dentry_upper(dentry) &&
             !ovl_matches_upper(dentry, upper))) {
                goto out_dput_upper;
        }

        whiteout = ovl_whiteout(workdir, dentry);
        err = PTR_ERR(whiteout);
        if (IS_ERR(whiteout))
                goto out_dput_upper;

        if (d_is_dir(upper))
                flags = RENAME_EXCHANGE;

        err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
        if (err)
                goto kill_whiteout;
        if (flags)
                ovl_cleanup(wdir, upper);

        ovl_dentry_version_inc(dentry->d_parent);
out_d_drop:
        d_drop(dentry);
        dput(whiteout);
out_dput_upper:
        dput(upper);
out_unlock:
        unlock_rename(workdir, upperdir);
out_dput:
        dput(opaquedir);
out:
        return err;

kill_whiteout:
        ovl_cleanup(wdir, whiteout);
        goto out_d_drop;
}

static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
{
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *dir = upperdir->d_inode;
        struct dentry *upper;
        struct dentry *opaquedir = NULL;
        int err;

        /* Redirect dir can be !ovl_lower_positive && OVL_TYPE_MERGE */
        if (is_dir && ovl_dentry_get_redirect(dentry)) {
                opaquedir = ovl_check_empty_and_clear(dentry);
                err = PTR_ERR(opaquedir);
                if (IS_ERR(opaquedir))
                        goto out;
        }

        inode_lock_nested(dir, I_MUTEX_PARENT);
        upper = lookup_one_len(dentry->d_name.name, upperdir,
                               dentry->d_name.len);
        err = PTR_ERR(upper);
        if (IS_ERR(upper))
                goto out_unlock;

        err = -ESTALE;
        if ((opaquedir && upper != opaquedir) ||
            (!opaquedir && !ovl_matches_upper(dentry, upper)))
                goto out_dput_upper;

        if (is_dir)
                err = vfs_rmdir(dir, upper);
        else
                err = vfs_unlink(dir, upper, NULL);
        ovl_dentry_version_inc(dentry->d_parent);

        /*
         * Keeping this dentry hashed would mean having to release
         * upperpath/lowerpath, which could only be done if we are the
         * sole user of this dentry.  Too tricky...  Just unhash for
         * now.
         */
        if (!err)
                d_drop(dentry);
out_dput_upper:
        dput(upper);
out_unlock:
        inode_unlock(dir);
        dput(opaquedir);
out:
        return err;
}

static int ovl_do_remove(struct dentry *dentry, bool is_dir)
{
        int err;
        bool locked = false;
        const struct cred *old_cred;

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        err = ovl_copy_up(dentry->d_parent);
        if (err)
                goto out_drop_write;

        err = ovl_nlink_start(dentry, &locked);
        if (err)
                goto out_drop_write;

        old_cred = ovl_override_creds(dentry->d_sb);
        if (!ovl_lower_positive(dentry))
                err = ovl_remove_upper(dentry, is_dir);
        else
                err = ovl_remove_and_whiteout(dentry, is_dir);
        revert_creds(old_cred);
        if (!err) {
                if (is_dir)
                        clear_nlink(dentry->d_inode);
                else
                        drop_nlink(dentry->d_inode);
        }
        ovl_nlink_end(dentry, locked);
out_drop_write:
        ovl_drop_write(dentry);
out:
        return err;
}

static int ovl_unlink(struct inode *dir, struct dentry *dentry)
{
        return ovl_do_remove(dentry, false);
}

static int ovl_rmdir(struct inode *dir, struct dentry *dentry)
{
        return ovl_do_remove(dentry, true);
}

static bool ovl_type_merge_or_lower(struct dentry *dentry)
{
        enum ovl_path_type type = ovl_path_type(dentry);

        return OVL_TYPE_MERGE(type) || !OVL_TYPE_UPPER(type);
}

static bool ovl_can_move(struct dentry *dentry)
{
        return ovl_redirect_dir(dentry->d_sb) ||
                !d_is_dir(dentry) || !ovl_type_merge_or_lower(dentry);
}

static char *ovl_get_redirect(struct dentry *dentry, bool samedir)
{
        char *buf, *ret;
        struct dentry *d, *tmp;
        int buflen = ovl_redirect_max + 1;

        if (samedir) {
                ret = kstrndup(dentry->d_name.name, dentry->d_name.len,
                               GFP_KERNEL);
                goto out;
        }

        buf = ret = kmalloc(buflen, GFP_TEMPORARY);
        if (!buf)
                goto out;

        buflen--;
        buf[buflen] = '\0';
        for (d = dget(dentry); !IS_ROOT(d);) {
                const char *name;
                int thislen;

                spin_lock(&d->d_lock);
                name = ovl_dentry_get_redirect(d);
                if (name) {
                        thislen = strlen(name);
                } else {
                        name = d->d_name.name;
                        thislen = d->d_name.len;
                }

                /* If path is too long, fall back to userspace move */
                if (thislen + (name[0] != '/') > buflen) {
                        ret = ERR_PTR(-EXDEV);
                        spin_unlock(&d->d_lock);
                        goto out_put;
                }

                buflen -= thislen;
                memcpy(&buf[buflen], name, thislen);
                tmp = dget_dlock(d->d_parent);
                spin_unlock(&d->d_lock);

                dput(d);
                d = tmp;

                /* Absolute redirect: finished */
                if (buf[buflen] == '/')
                        break;
                buflen--;
                buf[buflen] = '/';
        }
        ret = kstrdup(&buf[buflen], GFP_KERNEL);
out_put:
        dput(d);
        kfree(buf);
out:
        return ret ? ret : ERR_PTR(-ENOMEM);
}

static int ovl_set_redirect(struct dentry *dentry, bool samedir)
{
        int err;
        const char *redirect = ovl_dentry_get_redirect(dentry);

        if (redirect && (samedir || redirect[0] == '/'))
                return 0;

        redirect = ovl_get_redirect(dentry, samedir);
        if (IS_ERR(redirect))
                return PTR_ERR(redirect);

        err = ovl_check_setxattr(dentry, ovl_dentry_upper(dentry),
                                 OVL_XATTR_REDIRECT,
                                 redirect, strlen(redirect), -EXDEV);
        if (!err) {
                spin_lock(&dentry->d_lock);
                ovl_dentry_set_redirect(dentry, redirect);
                spin_unlock(&dentry->d_lock);
        } else {
                kfree(redirect);
                pr_warn_ratelimited("overlay: failed to set redirect (%i)\n", err);
                /* Fall back to userspace copy-up */
                err = -EXDEV;
        }
        return err;
}

static int ovl_rename(struct inode *olddir, struct dentry *old,
                      struct inode *newdir, struct dentry *new,
                      unsigned int flags)
{
        int err;
        bool locked = false;
        struct dentry *old_upperdir;
        struct dentry *new_upperdir;
        struct dentry *olddentry;
        struct dentry *newdentry;
        struct dentry *trap;
        bool old_opaque;
        bool new_opaque;
        bool cleanup_whiteout = false;
        bool overwrite = !(flags & RENAME_EXCHANGE);
        bool is_dir = d_is_dir(old);
        bool new_is_dir = d_is_dir(new);
        bool samedir = olddir == newdir;
        struct dentry *opaquedir = NULL;
        const struct cred *old_cred = NULL;

        err = -EINVAL;
        if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE))
                goto out;

        flags &= ~RENAME_NOREPLACE;

        /* Don't copy up directory trees */
        err = -EXDEV;
        if (!ovl_can_move(old))
                goto out;
        if (!overwrite && !ovl_can_move(new))
                goto out;

        err = ovl_want_write(old);
        if (err)
                goto out;

        err = ovl_copy_up(old);
        if (err)
                goto out_drop_write;

        err = ovl_copy_up(new->d_parent);
        if (err)
                goto out_drop_write;
        if (!overwrite) {
                err = ovl_copy_up(new);
                if (err)
                        goto out_drop_write;
        } else {
                err = ovl_nlink_start(new, &locked);
                if (err)
                        goto out_drop_write;
        }

        old_cred = ovl_override_creds(old->d_sb);

        if (overwrite && new_is_dir && ovl_type_merge_or_lower(new)) {
                opaquedir = ovl_check_empty_and_clear(new);
                err = PTR_ERR(opaquedir);
                if (IS_ERR(opaquedir)) {
                        opaquedir = NULL;
                        goto out_revert_creds;
                }
        }

        if (overwrite) {
                if (ovl_lower_positive(old)) {
                        if (!ovl_dentry_is_whiteout(new)) {
                                /* Whiteout source */
                                flags |= RENAME_WHITEOUT;
                        } else {
                                /* Switch whiteouts */
                                flags |= RENAME_EXCHANGE;
                        }
                } else if (is_dir && ovl_dentry_is_whiteout(new)) {
                        flags |= RENAME_EXCHANGE;
                        cleanup_whiteout = true;
                }
        }

        old_upperdir = ovl_dentry_upper(old->d_parent);
        new_upperdir = ovl_dentry_upper(new->d_parent);

        if (!samedir) {
                /*
                 * When moving a merge dir or non-dir with copy up origin into
                 * a new parent, we are marking the new parent dir "impure".
                 * When ovl_iterate() iterates an "impure" upper dir, it will

                 * lookup the origin inodes of the entries to fill d_ino.
                 */
                if (ovl_type_origin(old)) {
                        err = ovl_set_impure(new->d_parent, new_upperdir);
                        if (err)
                                goto out_revert_creds;
                }
                if (!overwrite && ovl_type_origin(new)) {
                        err = ovl_set_impure(old->d_parent, old_upperdir);
                        if (err)
                                goto out_revert_creds;
                }
        }

        trap = lock_rename(new_upperdir, old_upperdir);

        olddentry = lookup_one_len(old->d_name.name, old_upperdir,
                                   old->d_name.len);
        err = PTR_ERR(olddentry);
        if (IS_ERR(olddentry))
                goto out_unlock;

        err = -ESTALE;
        if (!ovl_matches_upper(old, olddentry))
                goto out_dput_old;

        newdentry = lookup_one_len(new->d_name.name, new_upperdir,
                                   new->d_name.len);
        err = PTR_ERR(newdentry);
        if (IS_ERR(newdentry))
                goto out_dput_old;

        old_opaque = ovl_dentry_is_opaque(old);
        new_opaque = ovl_dentry_is_opaque(new);

        err = -ESTALE;
        if (d_inode(new) && ovl_dentry_upper(new)) {
                if (opaquedir) {
                        if (newdentry != opaquedir)
                                goto out_dput;
                } else {
                        if (!ovl_matches_upper(new, newdentry))
                                goto out_dput;
                }
        } else {
                if (!d_is_negative(newdentry) &&
                    (!new_opaque || !ovl_is_whiteout(newdentry)))
                        goto out_dput;
        }

        if (olddentry == trap)
                goto out_dput;
        if (newdentry == trap)
                goto out_dput;

        if (WARN_ON(olddentry->d_inode == newdentry->d_inode))
                goto out_dput;

        err = 0;
        if (is_dir) {
                if (ovl_type_merge_or_lower(old))
                        err = ovl_set_redirect(old, samedir);
                else if (!old_opaque && ovl_type_merge(new->d_parent))
                        err = ovl_set_opaque_xerr(old, olddentry, -EXDEV);
                if (err)
                        goto out_dput;
        }
        if (!overwrite && new_is_dir) {
                if (ovl_type_merge_or_lower(new))
                        err = ovl_set_redirect(new, samedir);
                else if (!new_opaque && ovl_type_merge(old->d_parent))
                        err = ovl_set_opaque_xerr(new, newdentry, -EXDEV);
                if (err)
                        goto out_dput;
        }

        err = ovl_do_rename(old_upperdir->d_inode, olddentry,
                            new_upperdir->d_inode, newdentry, flags);
        if (err)
                goto out_dput;

        if (cleanup_whiteout)
                ovl_cleanup(old_upperdir->d_inode, newdentry);

        if (overwrite && d_inode(new)) {
                if (new_is_dir)
                        clear_nlink(d_inode(new));
                else
                        drop_nlink(d_inode(new));
        }

        ovl_dentry_version_inc(old->d_parent);
        ovl_dentry_version_inc(new->d_parent);

out_dput:
        dput(newdentry);
out_dput_old:
        dput(olddentry);
out_unlock:
        unlock_rename(new_upperdir, old_upperdir);
out_revert_creds:
        revert_creds(old_cred);
        ovl_nlink_end(new, locked);
out_drop_write:
        ovl_drop_write(old);
out:
        dput(opaquedir);
        return err;
}

const struct inode_operations ovl_dir_inode_operations = {
        .lookup         = ovl_lookup,
        .mkdir          = ovl_mkdir,
        .symlink        = ovl_symlink,
        .unlink         = ovl_unlink,
        .rmdir          = ovl_rmdir,
        .rename         = ovl_rename,
        .link           = ovl_link,
        .setattr        = ovl_setattr,
        .create         = ovl_create,
        .mknod          = ovl_mknod,
        .permission     = ovl_permission,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .get_acl        = ovl_get_acl,
        .update_time    = ovl_update_time,
};