// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * symlink.c - operations for configfs symlinks.
 *
 * Based on sysfs:
 *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
 *
 * configfs Copyright (C) 2005 Oracle.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/slab.h>

#include <linux/configfs.h>
#include "configfs_internal.h"

/* Protects attachments of new symlinks */
DEFINE_MUTEX(configfs_symlink_mutex);

static int item_depth(struct config_item * item)
{
        struct config_item * p = item;
        int depth = 0;
        do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
        return depth;
}

static int item_path_length(struct config_item * item)
{
        struct config_item * p = item;
        int length = 1;
        do {
                length += strlen(config_item_name(p)) + 1;
                p = p->ci_parent;
        } while (p && !configfs_is_root(p));
        return length;
}

static void fill_item_path(struct config_item * item, char * buffer, int length)
{
        struct config_item * p;

        --length;
        for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
                int cur = strlen(config_item_name(p));

                /* back up enough to print this bus id with '/' */
                length -= cur;
                memcpy(buffer + length, config_item_name(p), cur);
                *(buffer + --length) = '/';
        }
}

static int configfs_get_target_path(struct config_item *item,
                struct config_item *target, char *path)
{
        int depth, size;
        char *s;

        depth = item_depth(item);
        size = item_path_length(target) + depth * 3 - 1;
        if (size > PATH_MAX)
                return -ENAMETOOLONG;

        pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);

        for (s = path; depth--; s += 3)
                strcpy(s,"../");

        fill_item_path(target, path, size);
        pr_debug("%s: path = '%s'\n", __func__, path);
        return 0;
}

static int create_link(struct config_item *parent_item,
                       struct config_item *item,
                       struct dentry *dentry)
{
        struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
        char *body;
        int ret;

        if (!configfs_dirent_is_ready(target_sd))
                return -ENOENT;

        body = kzalloc(PAGE_SIZE, GFP_KERNEL);
        if (!body)
                return -ENOMEM;

        configfs_get(target_sd);
        spin_lock(&configfs_dirent_lock);
        if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
                spin_unlock(&configfs_dirent_lock);
                configfs_put(target_sd);
                kfree(body);
                return -ENOENT;
        }
        target_sd->s_links++;
        spin_unlock(&configfs_dirent_lock);
        ret = configfs_get_target_path(parent_item, item, body);
        if (!ret)
                ret = configfs_create_link(target_sd, parent_item->ci_dentry,
                                           dentry, body);
        if (ret) {
                spin_lock(&configfs_dirent_lock);
                target_sd->s_links--;
                spin_unlock(&configfs_dirent_lock);
                configfs_put(target_sd);
                kfree(body);
        }
        return ret;
}


static int get_target(const char *symname, struct config_item **target,
                      struct super_block *sb)
{
        struct path path __free(path_put) = {};
        int ret;

        ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &path);
        if (ret)
                return ret;
        if (path.dentry->d_sb != sb)
                return -EPERM;
        *target = configfs_get_config_item(path.dentry);
        if (!*target)
                return -ENOENT;
        return 0;
}


int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
                     struct dentry *dentry, const char *symname)
{
        int ret;
        struct configfs_dirent *sd;
        struct config_item *parent_item;
        struct config_item *target_item = NULL;
        const struct config_item_type *type;

        sd = dentry->d_parent->d_fsdata;
        /*
         * Fake invisibility if dir belongs to a group/default groups hierarchy
         * being attached
         */
        if (!configfs_dirent_is_ready(sd))
                return -ENOENT;

        parent_item = configfs_get_config_item(dentry->d_parent);
        type = parent_item->ci_type;

        ret = -EPERM;
        if (!type || !type->ct_item_ops ||
            !type->ct_item_ops->allow_link)
                goto out_put;

        /*
         * This is really sick.  What they wanted was a hybrid of
         * link(2) and symlink(2) - they wanted the target resolved
         * at syscall time (as link(2) would've done), be a directory
         * (which link(2) would've refused to do) *AND* be a deep
         * fucking magic, making the target busy from rmdir POV.
         * symlink(2) is nothing of that sort, and the locking it
         * gets matches the normal symlink(2) semantics.  Without
         * attempts to resolve the target (which might very well
         * not even exist yet) done prior to locking the parent
         * directory.  This perversion, OTOH, needs to resolve
         * the target, which would lead to obvious deadlocks if
         * attempted with any directories locked.
         *
         * Unfortunately, that garbage is userland ABI and we should've
         * said "no" back in 2005.  Too late now, so we get to
         * play very ugly games with locking.
         *
         * Try *ANYTHING* of that sort in new code, and you will
         * really regret it.  Just ask yourself - what could a BOFH
         * do to me and do I want to find it out first-hand?
         *
         *  AV, a thoroughly annoyed bastard.
         */
        inode_unlock(dir);
        ret = get_target(symname, &target_item, dentry->d_sb);
        inode_lock(dir);
        if (ret)
                goto out_put;

        if (dentry->d_inode || d_unhashed(dentry))
                ret = -EEXIST;
        else
                ret = inode_permission(&nop_mnt_idmap, dir,
                                       MAY_WRITE | MAY_EXEC);
        if (!ret)
                ret = type->ct_item_ops->allow_link(parent_item, target_item);
        if (!ret) {
                mutex_lock(&configfs_symlink_mutex);
                ret = create_link(parent_item, target_item, dentry);
                mutex_unlock(&configfs_symlink_mutex);
                if (ret && type->ct_item_ops->drop_link)
                        type->ct_item_ops->drop_link(parent_item,
                                                     target_item);
        }

        config_item_put(target_item);

out_put:
        config_item_put(parent_item);
        return ret;
}

int configfs_unlink(struct inode *dir, struct dentry *dentry)
{
        struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
        struct config_item *parent_item;
        const struct config_item_type *type;
        int ret;

        ret = -EPERM;  /* What lack-of-symlink returns */
        if (!(sd->s_type & CONFIGFS_ITEM_LINK))
                goto out;

        target_sd = sd->s_element;

        parent_item = configfs_get_config_item(dentry->d_parent);
        type = parent_item->ci_type;

        spin_lock(&configfs_dirent_lock);
        list_del_init(&sd->s_sibling);
        spin_unlock(&configfs_dirent_lock);
        configfs_drop_dentry(sd, dentry->d_parent);
        dput(dentry);
        configfs_put(sd);

        /*
         * drop_link() must be called before
         * decrementing target's ->s_links, so that the order of
         * drop_link(this, target) and drop_item(target) is preserved.
         */
        if (type && type->ct_item_ops &&
            type->ct_item_ops->drop_link)
                type->ct_item_ops->drop_link(parent_item,
                                               target_sd->s_element);

        spin_lock(&configfs_dirent_lock);
        target_sd->s_links--;
        spin_unlock(&configfs_dirent_lock);
        configfs_put(target_sd);

        config_item_put(parent_item);

        ret = 0;

out:
        return ret;
}

const struct inode_operations configfs_symlink_inode_operations = {
        .get_link = simple_get_link,
        .setattr = configfs_setattr,
};