utsname.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 *  Copyright (C) 2004 IBM Corporation
  4 *
  5 *  Author: Serge Hallyn <serue@us.ibm.com>
  6 */
  7
  8#include <linux/export.h>
  9#include <linux/uts.h>
 10#include <linux/utsname.h>
 11#include <linux/err.h>
 12#include <linux/slab.h>
 13#include <linux/cred.h>
 14#include <linux/user_namespace.h>
 15#include <linux/proc_ns.h>
 16#include <linux/nstree.h>
 17#include <linux/sched/task.h>
 18
 19static struct kmem_cache *uts_ns_cache __ro_after_init;
 20
 21static struct ucounts *inc_uts_namespaces(struct user_namespace *ns)
 22{
 23	return inc_ucount(ns, current_euid(), UCOUNT_UTS_NAMESPACES);
 24}
 25
 26static void dec_uts_namespaces(struct ucounts *ucounts)
 27{
 28	dec_ucount(ucounts, UCOUNT_UTS_NAMESPACES);
 29}
 30
 31/*
 32 * Clone a new ns copying an original utsname, setting refcount to 1
 33 * @old_ns: namespace to clone
 34 * Return ERR_PTR(-ENOMEM) on error (failure to allocate), new ns otherwise
 35 */
 36static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 37					  struct uts_namespace *old_ns)
 38{
 39	struct uts_namespace *ns;
 40	struct ucounts *ucounts;
 41	int err;
 42
 43	err = -ENOSPC;
 44	ucounts = inc_uts_namespaces(user_ns);
 45	if (!ucounts)
 46		goto fail;
 47
 48	err = -ENOMEM;
 49	ns = kmem_cache_zalloc(uts_ns_cache, GFP_KERNEL);
 50	if (!ns)
 51		goto fail_dec;
 52
 53	err = ns_common_init(ns);
 54	if (err)
 55		goto fail_free;
 56
 57	ns->ucounts = ucounts;
 58	down_read(&uts_sem);
 59	memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
 60	ns->user_ns = get_user_ns(user_ns);
 61	up_read(&uts_sem);
 62	ns_tree_add(ns);
 63	return ns;
 64
 65fail_free:
 66	kmem_cache_free(uts_ns_cache, ns);
 67fail_dec:
 68	dec_uts_namespaces(ucounts);
 69fail:
 70	return ERR_PTR(err);
 71}
 72
 73/*
 74 * Copy task tsk's utsname namespace, or clone it if flags
 75 * specifies CLONE_NEWUTS.  In latter case, changes to the
 76 * utsname of this process won't be seen by parent, and vice
 77 * versa.
 78 */
 79struct uts_namespace *copy_utsname(u64 flags,
 80	struct user_namespace *user_ns, struct uts_namespace *old_ns)
 81{
 82	struct uts_namespace *new_ns;
 83
 84	BUG_ON(!old_ns);
 85	get_uts_ns(old_ns);
 86
 87	if (!(flags & CLONE_NEWUTS))
 88		return old_ns;
 89
 90	new_ns = clone_uts_ns(user_ns, old_ns);
 91
 92	put_uts_ns(old_ns);
 93	return new_ns;
 94}
 95
 96void free_uts_ns(struct uts_namespace *ns)
 97{
 98	ns_tree_remove(ns);
 99	dec_uts_namespaces(ns->ucounts);
100	put_user_ns(ns->user_ns);
101	ns_common_free(ns);
102	/* Concurrent nstree traversal depends on a grace period. */
103	kfree_rcu(ns, ns.ns_rcu);
104}
105
106static struct ns_common *utsns_get(struct task_struct *task)
107{
108	struct uts_namespace *ns = NULL;
109	struct nsproxy *nsproxy;
110
111	task_lock(task);
112	nsproxy = task->nsproxy;
113	if (nsproxy) {
114		ns = nsproxy->uts_ns;
115		get_uts_ns(ns);
116	}
117	task_unlock(task);
118
119	return ns ? &ns->ns : NULL;
120}
121
122static void utsns_put(struct ns_common *ns)
123{
124	put_uts_ns(to_uts_ns(ns));
125}
126
127static int utsns_install(struct nsset *nsset, struct ns_common *new)
128{
129	struct nsproxy *nsproxy = nsset->nsproxy;
130	struct uts_namespace *ns = to_uts_ns(new);
131
132	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
133	    !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
134		return -EPERM;
135
136	get_uts_ns(ns);
137	put_uts_ns(nsproxy->uts_ns);
138	nsproxy->uts_ns = ns;
139	return 0;
140}
141
142static struct user_namespace *utsns_owner(struct ns_common *ns)
143{
144	return to_uts_ns(ns)->user_ns;
145}
146
147const struct proc_ns_operations utsns_operations = {
148	.name		= "uts",
149	.get		= utsns_get,
150	.put		= utsns_put,
151	.install	= utsns_install,
152	.owner		= utsns_owner,
153};
154
155void __init uts_ns_init(void)
156{
157	uts_ns_cache = kmem_cache_create_usercopy(
158			"uts_namespace", sizeof(struct uts_namespace), 0,
159			SLAB_PANIC|SLAB_ACCOUNT,
160			offsetof(struct uts_namespace, name),
161			sizeof_field(struct uts_namespace, name),
162			NULL);
163	ns_tree_add(&init_uts_ns);
164}