// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Copyright (C) 2004 IBM Corporation
 *
 *  Author: Serge Hallyn <serue@us.ibm.com>
 */

#include <linux/export.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/user_namespace.h>
#include <linux/proc_ns.h>
#include <linux/nstree.h>
#include <linux/sched/task.h>

static struct kmem_cache *uts_ns_cache __ro_after_init;

static struct ucounts *inc_uts_namespaces(struct user_namespace *ns)
{
        return inc_ucount(ns, current_euid(), UCOUNT_UTS_NAMESPACES);
}

static void dec_uts_namespaces(struct ucounts *ucounts)
{
        dec_ucount(ucounts, UCOUNT_UTS_NAMESPACES);
}

/*
 * Clone a new ns copying an original utsname, setting refcount to 1
 * @old_ns: namespace to clone
 * Return ERR_PTR(-ENOMEM) on error (failure to allocate), new ns otherwise
 */
static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
                                          struct uts_namespace *old_ns)
{
        struct uts_namespace *ns;
        struct ucounts *ucounts;
        int err;

        err = -ENOSPC;
        ucounts = inc_uts_namespaces(user_ns);
        if (!ucounts)
                goto fail;

        err = -ENOMEM;
        ns = kmem_cache_zalloc(uts_ns_cache, GFP_KERNEL);
        if (!ns)
                goto fail_dec;

        err = ns_common_init(ns);
        if (err)
                goto fail_free;

        ns->ucounts = ucounts;
        down_read(&uts_sem);
        memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
        ns->user_ns = get_user_ns(user_ns);
        up_read(&uts_sem);
        ns_tree_add(ns);
        return ns;

fail_free:
        kmem_cache_free(uts_ns_cache, ns);
fail_dec:
        dec_uts_namespaces(ucounts);
fail:
        return ERR_PTR(err);
}

/*
 * Copy task tsk's utsname namespace, or clone it if flags
 * specifies CLONE_NEWUTS.  In latter case, changes to the
 * utsname of this process won't be seen by parent, and vice
 * versa.
 */
struct uts_namespace *copy_utsname(u64 flags,
        struct user_namespace *user_ns, struct uts_namespace *old_ns)
{
        struct uts_namespace *new_ns;

        BUG_ON(!old_ns);
        get_uts_ns(old_ns);

        if (!(flags & CLONE_NEWUTS))
                return old_ns;

        new_ns = clone_uts_ns(user_ns, old_ns);

        put_uts_ns(old_ns);
        return new_ns;
}

void free_uts_ns(struct uts_namespace *ns)
{
        ns_tree_remove(ns);
        dec_uts_namespaces(ns->ucounts);
        put_user_ns(ns->user_ns);
        ns_common_free(ns);
        /* Concurrent nstree traversal depends on a grace period. */
        kfree_rcu(ns, ns.ns_rcu);
}

static struct ns_common *utsns_get(struct task_struct *task)
{
        struct uts_namespace *ns = NULL;
        struct nsproxy *nsproxy;

        task_lock(task);
        nsproxy = task->nsproxy;
        if (nsproxy) {
                ns = nsproxy->uts_ns;
                get_uts_ns(ns);
        }
        task_unlock(task);

        return ns ? &ns->ns : NULL;
}

static void utsns_put(struct ns_common *ns)
{
        put_uts_ns(to_uts_ns(ns));
}

static int utsns_install(struct nsset *nsset, struct ns_common *new)
{
        struct nsproxy *nsproxy = nsset->nsproxy;
        struct uts_namespace *ns = to_uts_ns(new);

        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
            !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
                return -EPERM;

        get_uts_ns(ns);
        put_uts_ns(nsproxy->uts_ns);
        nsproxy->uts_ns = ns;
        return 0;
}

static struct user_namespace *utsns_owner(struct ns_common *ns)
{
        return to_uts_ns(ns)->user_ns;
}

const struct proc_ns_operations utsns_operations = {
        .name           = "uts",
        .get            = utsns_get,
        .put            = utsns_put,
        .install        = utsns_install,
        .owner          = utsns_owner,
};

void __init uts_ns_init(void)
{
        uts_ns_cache = kmem_cache_create_usercopy(
                        "uts_namespace", sizeof(struct uts_namespace), 0,
                        SLAB_PANIC|SLAB_ACCOUNT,
                        offsetof(struct uts_namespace, name),
                        sizeof_field(struct uts_namespace, name),
                        NULL);
        ns_tree_add(&init_uts_ns);
}