// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Copyright (C) 2011 Novell Inc.
 */

#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(redirect_max,
                 "Maximum length of absolute redirect xattr value");

static int ovl_set_redirect(struct dentry *dentry, bool samedir);

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("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("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 ovl_fs *ofs)
{
        int err;
        struct dentry *whiteout;
        struct dentry *workdir = ofs->workdir;
        struct inode *wdir = workdir->d_inode;

        if (!ofs->whiteout) {
                whiteout = ovl_lookup_temp(workdir);
                if (IS_ERR(whiteout))
                        goto out;

                err = ovl_do_whiteout(wdir, whiteout);
                if (err) {
                        dput(whiteout);
                        whiteout = ERR_PTR(err);
                        goto out;
                }
                ofs->whiteout = whiteout;
        }

        if (ofs->share_whiteout) {
                whiteout = ovl_lookup_temp(workdir);
                if (IS_ERR(whiteout))
                        goto out;

                err = ovl_do_link(ofs->whiteout, wdir, whiteout);
                if (!err)
                        goto out;

                if (err != -EMLINK) {
                        pr_warn("Failed to link whiteout - disabling whiteout inode sharing(nlink=%u, err=%i)\n",
                                ofs->whiteout->d_inode->i_nlink, err);
                        ofs->share_whiteout = false;
                }
                dput(whiteout);
        }
        whiteout = ofs->whiteout;
        ofs->whiteout = NULL;
out:
        return whiteout;
}

/* Caller must hold i_mutex on both workdir and dir */
int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct inode *dir,
                             struct dentry *dentry)
{
        struct inode *wdir = ofs->workdir->d_inode;
        struct dentry *whiteout;
        int err;
        int flags = 0;

        whiteout = ovl_whiteout(ofs);
        err = PTR_ERR(whiteout);
        if (IS_ERR(whiteout))
                return err;

        if (d_is_dir(dentry))
                flags = RENAME_EXCHANGE;

        err = ovl_do_rename(wdir, whiteout, dir, dentry, flags);
        if (err)
                goto kill_whiteout;
        if (flags)
                ovl_cleanup(wdir, dentry);

out:
        dput(whiteout);
        return err;

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

static int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry,
                          umode_t mode)
{
        int err;
        struct dentry *d, *dentry = *newdentry;

        err = ovl_do_mkdir(dir, dentry, mode);
        if (err)
                return err;

        if (likely(!d_unhashed(dentry)))
                return 0;

        /*
         * vfs_mkdir() may succeed and leave the dentry passed
         * to it unhashed and negative. If that happens, try to
         * lookup a new hashed and positive dentry.
         */
        d = lookup_one_len(dentry->d_name.name, dentry->d_parent,
                           dentry->d_name.len);
        if (IS_ERR(d)) {
                pr_warn("failed lookup after mkdir (%pd2, err=%i).\n",
                        dentry, err);
                return PTR_ERR(d);
        }
        dput(dentry);
        *newdentry = d;

        return 0;
}

struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
                               struct ovl_cattr *attr)
{
        int err;

        if (IS_ERR(newdentry))
                return newdentry;

        err = -ESTALE;
        if (newdentry->d_inode)
                goto out;

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

                case S_IFDIR:
                        /* mkdir is special... */
                        err =  ovl_mkdir_real(dir, &newdentry, attr->mode);
                        break;

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

                case S_IFLNK:
                        err = ovl_do_symlink(dir, newdentry, attr->link);
                        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 = -EIO;
        }
out:
        if (err) {
                dput(newdentry);
                return ERR_PTR(err);
        }
        return newdentry;
}

struct dentry *ovl_create_temp(struct dentry *workdir, struct ovl_cattr *attr)
{
        return ovl_create_real(d_inode(workdir), ovl_lookup_temp(workdir),
                               attr);
}

static int ovl_set_opaque_xerr(struct dentry *dentry, struct dentry *upper,
                               int xerr)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        int err;

        err = ovl_check_setxattr(ofs, 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.
 * If @hardlink is false, then @inode is a pre-allocated inode, we may or
 * may not use to instantiate the new dentry.
 */
static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
                           struct dentry *newdentry, bool hardlink)
{
        struct ovl_inode_params oip = {
                .upperdentry = newdentry,
                .newinode = inode,
        };

        ovl_dir_modified(dentry->d_parent, false);
        ovl_dentry_set_upper_alias(dentry);
        ovl_dentry_update_reval(dentry, newdentry,
                        DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);

        if (!hardlink) {
                /*
                 * ovl_obtain_alias() can be called after ovl_create_real()
                 * and before we get here, so we may get an inode from cache
                 * with the same real upperdentry that is not the inode we
                 * pre-allocated.  In this case we will use the cached inode
                 * to instantiate the new dentry.
                 *
                 * XXX: if we ever use ovl_obtain_alias() to decode directory
                 * file handles, need to use ovl_get_inode_locked() and
                 * d_instantiate_new() here to prevent from creating two
                 * hashed directory inode aliases.
                 */
                inode = ovl_get_inode(dentry->d_sb, &oip);
                if (IS_ERR(inode))
                        return PTR_ERR(inode);
                if (inode == oip.newinode)
                        ovl_set_flag(OVL_UPPERDATA, inode);
        } else {
                WARN_ON(ovl_inode_real(inode) != d_inode(newdentry));
                dput(newdentry);
                inc_nlink(inode);
        }

        d_instantiate(dentry, inode);
        if (inode != oip.newinode) {
                pr_warn_ratelimited("newly created inode found in cache (%pd2)\n",
                                    dentry);
        }

        /* Force lookup of new upper hardlink to find its lower */
        if (hardlink)
                d_drop(dentry);

        return 0;
}

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 ovl_cattr *attr)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *udir = upperdir->d_inode;
        struct dentry *newdentry;
        int err;

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

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

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

        err = ovl_instantiate(dentry, inode, newdentry, !!attr->hardlink);
        if (err)
                goto out_cleanup;
out_unlock:
        inode_unlock(udir);
        return err;

out_cleanup:
        ovl_cleanup(udir, newdentry);
        dput(newdentry);
        goto out_unlock;
}

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_create_temp(workdir, OVL_CATTR(stat.mode));
        err = PTR_ERR(opaquedir);
        if (IS_ERR(opaquedir))
                goto out_unlock;

        err = ovl_copy_xattr(dentry->d_sb, 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);
        dput(opaquedir);
out_unlock:
        unlock_rename(workdir, upperdir);
out:
        return ERR_PTR(err);
}

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_xattr_size(acl->a_count);
        buffer = kmalloc(size, GFP_KERNEL);
        if (!buffer)
                return -ENOMEM;

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

        err = vfs_setxattr(&init_user_ns, 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 ovl_cattr *cattr)
{
        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;
        bool hardlink = !!cattr->hardlink;

        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;

        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 (d_is_negative(upper) || !IS_WHITEOUT(d_inode(upper)))
                goto out_dput;

        newdentry = ovl_create_temp(workdir, cattr);
        err = PTR_ERR(newdentry);
        if (IS_ERR(newdentry))
                goto out_dput;

        /*
         * 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(&init_user_ns, 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;
        }
        err = ovl_instantiate(dentry, inode, newdentry, hardlink);
        if (err) {
                ovl_cleanup(udir, newdentry);
                dput(newdentry);
        }
out_dput:
        dput(upper);
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);
        dput(newdentry);
        goto out_dput;
}

static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
                              struct ovl_cattr *attr, 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 (!attr->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);
                else
                        err = ovl_create_over_whiteout(dentry, inode, attr);
        }
out_revert_creds:
        revert_creds(old_cred);
        return err;
}

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

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

        /* Preallocate inode to be used by ovl_get_inode() */
        err = -ENOMEM;
        inode = ovl_new_inode(dentry->d_sb, mode, rdev);
        if (!inode)
                goto out_drop_write;

        spin_lock(&inode->i_lock);
        inode->i_state |= I_CREATING;
        spin_unlock(&inode->i_lock);

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

        err = ovl_create_or_link(dentry, inode, &attr, false);
        /* Did we end up using the preallocated inode? */
        if (inode != d_inode(dentry))
                iput(inode);

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

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

static int ovl_set_link_redirect(struct dentry *dentry)
{
        const struct cred *old_cred;
        int err;

        old_cred = ovl_override_creds(dentry->d_sb);
        err = ovl_set_redirect(dentry, false);
        revert_creds(old_cred);

        return err;
}

static int ovl_link(struct dentry *old, struct inode *newdir,
                    struct dentry *new)
{
        int err;
        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_copy_up(new->d_parent);
        if (err)
                goto out_drop_write;

        if (ovl_is_metacopy_dentry(old)) {
                err = ovl_set_link_redirect(old);
                if (err)
                        goto out_drop_write;
        }

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

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

        err = ovl_create_or_link(new, inode,
                        &(struct ovl_cattr) {.hardlink = ovl_dentry_upper(old)},
                        ovl_type_origin(old));
        if (err)
                iput(inode);

        ovl_nlink_end(old);
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,
                                   struct list_head *list)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct dentry *workdir = ovl_workdir(dentry);
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct dentry *upper;
        struct dentry *opaquedir = NULL;
        int err;

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

        if (!list_empty(list)) {
                opaquedir = ovl_clear_empty(dentry, list);
                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;
        }

        err = ovl_cleanup_and_whiteout(ofs, d_inode(upperdir), upper);
        if (err)
                goto out_d_drop;

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

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

        if (!list_empty(list)) {
                opaquedir = ovl_clear_empty(dentry, list);
                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(&init_user_ns, dir, upper);
        else
                err = vfs_unlink(&init_user_ns, dir, upper, NULL);
        ovl_dir_modified(dentry->d_parent, ovl_type_origin(dentry));

        /*
         * 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 bool ovl_pure_upper(struct dentry *dentry)
{
        return !ovl_dentry_lower(dentry) &&
               !ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
}

static void ovl_drop_nlink(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        struct dentry *alias;

        /* Try to find another, hashed alias */
        spin_lock(&inode->i_lock);
        hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
                if (alias != dentry && !d_unhashed(alias))
                        break;
        }
        spin_unlock(&inode->i_lock);

        /*
         * Changes to underlying layers may cause i_nlink to lose sync with
         * reality.  In this case prevent the link count from going to zero
         * prematurely.
         */
        if (inode->i_nlink > !!alias)
                drop_nlink(inode);
}

static int ovl_do_remove(struct dentry *dentry, bool is_dir)
{
        int err;
        const struct cred *old_cred;
        struct dentry *upperdentry;
        bool lower_positive = ovl_lower_positive(dentry);
        LIST_HEAD(list);

        /* No need to clean pure upper removed by vfs_rmdir() */
        if (is_dir && (lower_positive || !ovl_pure_upper(dentry))) {
                err = ovl_check_empty_dir(dentry, &list);
                if (err)
                        goto out;
        }

        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);
        if (err)
                goto out_drop_write;

        old_cred = ovl_override_creds(dentry->d_sb);
        if (!lower_positive)
                err = ovl_remove_upper(dentry, is_dir, &list);
        else
                err = ovl_remove_and_whiteout(dentry, &list);
        revert_creds(old_cred);
        if (!err) {
                if (is_dir)
                        clear_nlink(dentry->d_inode);
                else
                        ovl_drop_nlink(dentry);
        }
        ovl_nlink_end(dentry);

        /*
         * Copy ctime
         *
         * Note: we fail to update ctime if there was no copy-up, only a
         * whiteout
         */
        upperdentry = ovl_dentry_upper(dentry);
        if (upperdentry)
                ovl_copyattr(d_inode(upperdentry), d_inode(dentry));

out_drop_write:
        ovl_drop_write(dentry);
out:
        ovl_cache_free(&list);
        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 abs_redirect)
{
        char *buf, *ret;
        struct dentry *d, *tmp;
        int buflen = ovl_redirect_max + 1;

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

        buf = ret = kmalloc(buflen, GFP_KERNEL);
        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);

                spin_unlock(&d->d_lock);
                tmp = dget_parent(d);

                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 bool ovl_need_absolute_redirect(struct dentry *dentry, bool samedir)
{
        struct dentry *lowerdentry;

        if (!samedir)
                return true;

        if (d_is_dir(dentry))
                return false;

        /*
         * For non-dir hardlinked files, we need absolute redirects
         * in general as two upper hardlinks could be in different
         * dirs. We could put a relative redirect now and convert
         * it to absolute redirect later. But when nlink > 1 and
         * indexing is on, that means relative redirect needs to be
         * converted to absolute during copy up of another lower
         * hardllink as well.
         *
         * So without optimizing too much, just check if lower is
         * a hard link or not. If lower is hard link, put absolute
         * redirect.
         */
        lowerdentry = ovl_dentry_lower(dentry);
        return (d_inode(lowerdentry)->i_nlink > 1);
}

static int ovl_set_redirect(struct dentry *dentry, bool samedir)
{
        int err;
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        const char *redirect = ovl_dentry_get_redirect(dentry);
        bool absolute_redirect = ovl_need_absolute_redirect(dentry, samedir);

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

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

        err = ovl_check_setxattr(ofs, 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("failed to set redirect (%i)\n",
                                    err);
                /* Fall back to userspace copy-up */
                err = -EXDEV;
        }
        return err;
}

static int ovl_rename(struct user_namespace *mnt_userns, struct inode *olddir,
                      struct dentry *old, struct inode *newdir,
                      struct dentry *new, unsigned int flags)
{
        int err;
        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 update_nlink = 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;
        LIST_HEAD(list);

        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;

        if (overwrite && new_is_dir && !ovl_pure_upper(new)) {
                err = ovl_check_empty_dir(new, &list);
                if (err)
                        goto out;
        }

        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;
                }
        }

        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 if (d_inode(new)) {
                err = ovl_nlink_start(new);
                if (err)
                        goto out_drop_write;

                update_nlink = true;
        }

        old_cred = ovl_override_creds(old->d_sb);

        if (!list_empty(&list)) {
                opaquedir = ovl_clear_empty(new, &list);
                err = PTR_ERR(opaquedir);
                if (IS_ERR(opaquedir)) {
                        opaquedir = NULL;
                        goto out_revert_creds;
                }
        }

        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)) {
                        if (!new_opaque || !ovl_is_whiteout(newdentry))
                                goto out_dput;
                } else {
                        if (flags & RENAME_EXCHANGE)
                                goto out_dput;
                }
        }

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

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

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

        if (!overwrite && ovl_type_merge_or_lower(new))
                err = ovl_set_redirect(new, samedir);
        else if (!overwrite && new_is_dir && !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
                        ovl_drop_nlink(new);
        }

        ovl_dir_modified(old->d_parent, ovl_type_origin(old) ||
                         (!overwrite && ovl_type_origin(new)));
        ovl_dir_modified(new->d_parent, ovl_type_origin(old) ||
                         (d_inode(new) && ovl_type_origin(new)));

        /* copy ctime: */
        ovl_copyattr(d_inode(olddentry), d_inode(old));
        if (d_inode(new) && ovl_dentry_upper(new))
                ovl_copyattr(d_inode(newdentry), d_inode(new));

out_dput:
        dput(newdentry);
out_dput_old:
        dput(olddentry);
out_unlock:
        unlock_rename(new_upperdir, old_upperdir);
out_revert_creds:
        revert_creds(old_cred);
        if (update_nlink)
                ovl_nlink_end(new);
out_drop_write:
        ovl_drop_write(old);
out:
        dput(opaquedir);
        ovl_cache_free(&list);
        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,
        .fileattr_get   = ovl_fileattr_get,
        .fileattr_set   = ovl_fileattr_set,
};