// SPDX-License-Identifier: GPL-2.0-only
/*
 * fs/kernfs/symlink.c - kernfs symlink implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
 */

#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/namei.h>

#include "kernfs-internal.h"

/**
 * kernfs_create_link - create a symlink
 * @parent: directory to create the symlink in
 * @name: name of the symlink
 * @target: target node for the symlink to point to
 *
 * Return: the created node on success, ERR_PTR() value on error.
 * Ownership of the link matches ownership of the target.
 */
struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
                                       const char *name,
                                       struct kernfs_node *target)
{
        struct kernfs_node *kn;
        int error;
        kuid_t uid = GLOBAL_ROOT_UID;
        kgid_t gid = GLOBAL_ROOT_GID;

        if (target->iattr) {
                uid = target->iattr->ia_uid;
                gid = target->iattr->ia_gid;
        }

        kn = kernfs_new_node(parent, name, S_IFLNK|0777, uid, gid, KERNFS_LINK);
        if (!kn)
                return ERR_PTR(-ENOMEM);

        if (kernfs_ns_enabled(parent))
                kn->ns = target->ns;
        kn->symlink.target_kn = target;
        kernfs_get(target);     /* ref owned by symlink */

        error = kernfs_add_one(kn);
        if (!error)
                return kn;

        kernfs_put(kn);
        return ERR_PTR(error);
}

static int kernfs_get_target_path(struct kernfs_node *parent,
                                  struct kernfs_node *target, char *path)
{
        struct kernfs_node *base, *kn;
        char *s = path;
        int len = 0;

        /* go up to the root, stop at the base */
        base = parent;
        while (kernfs_parent(base)) {
                kn = kernfs_parent(target);
                while (kernfs_parent(kn) && base != kn)
                        kn = kernfs_parent(kn);

                if (base == kn)
                        break;

                if ((s - path) + 3 >= PATH_MAX)
                        return -ENAMETOOLONG;

                strcpy(s, "../");
                s += 3;
                base = kernfs_parent(base);
        }

        /* determine end of target string for reverse fillup */
        kn = target;
        while (kernfs_parent(kn) && kn != base) {
                len += strlen(kernfs_rcu_name(kn)) + 1;
                kn = kernfs_parent(kn);
        }

        /* check limits */
        if (len < 2)
                return -EINVAL;
        len--;
        if ((s - path) + len >= PATH_MAX)
                return -ENAMETOOLONG;

        /* reverse fillup of target string from target to base */
        kn = target;
        while (kernfs_parent(kn) && kn != base) {
                const char *name = kernfs_rcu_name(kn);
                int slen = strlen(name);

                len -= slen;
                memcpy(s + len, name, slen);
                if (len)
                        s[--len] = '/';

                kn = kernfs_parent(kn);
        }

        return 0;
}

static int kernfs_getlink(struct inode *inode, char *path)
{
        struct kernfs_node *kn = inode->i_private;
        struct kernfs_node *parent;
        struct kernfs_node *target = kn->symlink.target_kn;
        struct kernfs_root *root = kernfs_root(kn);
        int error;

        down_read(&root->kernfs_rwsem);
        parent = kernfs_parent(kn);
        error = kernfs_get_target_path(parent, target, path);
        up_read(&root->kernfs_rwsem);

        return error;
}

static const char *kernfs_iop_get_link(struct dentry *dentry,
                                       struct inode *inode,
                                       struct delayed_call *done)
{
        char *body;
        int error;

        if (!dentry)
                return ERR_PTR(-ECHILD);
        body = kzalloc(PAGE_SIZE, GFP_KERNEL);
        if (!body)
                return ERR_PTR(-ENOMEM);
        error = kernfs_getlink(inode, body);
        if (unlikely(error < 0)) {
                kfree(body);
                return ERR_PTR(error);
        }
        set_delayed_call(done, kfree_link, body);
        return body;
}

const struct inode_operations kernfs_symlink_iops = {
        .listxattr      = kernfs_iop_listxattr,
        .get_link       = kernfs_iop_get_link,
        .setattr        = kernfs_iop_setattr,
        .getattr        = kernfs_iop_getattr,
        .permission     = kernfs_iop_permission,
};