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Linux/kernel/utsname.c

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  1 /*
  2  *  Copyright (C) 2004 IBM Corporation
  3  *
  4  *  Author: Serge Hallyn <serue@us.ibm.com>
  5  *
  6  *  This program is free software; you can redistribute it and/or
  7  *  modify it under the terms of the GNU General Public License as
  8  *  published by the Free Software Foundation, version 2 of the
  9  *  License.
 10  */
 11 
 12 #include <linux/export.h>
 13 #include <linux/uts.h>
 14 #include <linux/utsname.h>
 15 #include <linux/err.h>
 16 #include <linux/slab.h>
 17 #include <linux/cred.h>
 18 #include <linux/user_namespace.h>
 19 #include <linux/proc_ns.h>
 20 #include <linux/sched/task.h>
 21 
 22 static struct kmem_cache *uts_ns_cache __ro_after_init;
 23 
 24 static struct ucounts *inc_uts_namespaces(struct user_namespace *ns)
 25 {
 26         return inc_ucount(ns, current_euid(), UCOUNT_UTS_NAMESPACES);
 27 }
 28 
 29 static void dec_uts_namespaces(struct ucounts *ucounts)
 30 {
 31         dec_ucount(ucounts, UCOUNT_UTS_NAMESPACES);
 32 }
 33 
 34 static struct uts_namespace *create_uts_ns(void)
 35 {
 36         struct uts_namespace *uts_ns;
 37 
 38         uts_ns = kmem_cache_alloc(uts_ns_cache, GFP_KERNEL);
 39         if (uts_ns)
 40                 kref_init(&uts_ns->kref);
 41         return uts_ns;
 42 }
 43 
 44 /*
 45  * Clone a new ns copying an original utsname, setting refcount to 1
 46  * @old_ns: namespace to clone
 47  * Return ERR_PTR(-ENOMEM) on error (failure to allocate), new ns otherwise
 48  */
 49 static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 50                                           struct uts_namespace *old_ns)
 51 {
 52         struct uts_namespace *ns;
 53         struct ucounts *ucounts;
 54         int err;
 55 
 56         err = -ENOSPC;
 57         ucounts = inc_uts_namespaces(user_ns);
 58         if (!ucounts)
 59                 goto fail;
 60 
 61         err = -ENOMEM;
 62         ns = create_uts_ns();
 63         if (!ns)
 64                 goto fail_dec;
 65 
 66         err = ns_alloc_inum(&ns->ns);
 67         if (err)
 68                 goto fail_free;
 69 
 70         ns->ucounts = ucounts;
 71         ns->ns.ops = &utsns_operations;
 72 
 73         down_read(&uts_sem);
 74         memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
 75         ns->user_ns = get_user_ns(user_ns);
 76         up_read(&uts_sem);
 77         return ns;
 78 
 79 fail_free:
 80         kmem_cache_free(uts_ns_cache, ns);
 81 fail_dec:
 82         dec_uts_namespaces(ucounts);
 83 fail:
 84         return ERR_PTR(err);
 85 }
 86 
 87 /*
 88  * Copy task tsk's utsname namespace, or clone it if flags
 89  * specifies CLONE_NEWUTS.  In latter case, changes to the
 90  * utsname of this process won't be seen by parent, and vice
 91  * versa.
 92  */
 93 struct uts_namespace *copy_utsname(unsigned long flags,
 94         struct user_namespace *user_ns, struct uts_namespace *old_ns)
 95 {
 96         struct uts_namespace *new_ns;
 97 
 98         BUG_ON(!old_ns);
 99         get_uts_ns(old_ns);
100 
101         if (!(flags & CLONE_NEWUTS))
102                 return old_ns;
103 
104         new_ns = clone_uts_ns(user_ns, old_ns);
105 
106         put_uts_ns(old_ns);
107         return new_ns;
108 }
109 
110 void free_uts_ns(struct kref *kref)
111 {
112         struct uts_namespace *ns;
113 
114         ns = container_of(kref, struct uts_namespace, kref);
115         dec_uts_namespaces(ns->ucounts);
116         put_user_ns(ns->user_ns);
117         ns_free_inum(&ns->ns);
118         kmem_cache_free(uts_ns_cache, ns);
119 }
120 
121 static inline struct uts_namespace *to_uts_ns(struct ns_common *ns)
122 {
123         return container_of(ns, struct uts_namespace, ns);
124 }
125 
126 static struct ns_common *utsns_get(struct task_struct *task)
127 {
128         struct uts_namespace *ns = NULL;
129         struct nsproxy *nsproxy;
130 
131         task_lock(task);
132         nsproxy = task->nsproxy;
133         if (nsproxy) {
134                 ns = nsproxy->uts_ns;
135                 get_uts_ns(ns);
136         }
137         task_unlock(task);
138 
139         return ns ? &ns->ns : NULL;
140 }
141 
142 static void utsns_put(struct ns_common *ns)
143 {
144         put_uts_ns(to_uts_ns(ns));
145 }
146 
147 static int utsns_install(struct nsproxy *nsproxy, struct ns_common *new)
148 {
149         struct uts_namespace *ns = to_uts_ns(new);
150 
151         if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
152             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
153                 return -EPERM;
154 
155         get_uts_ns(ns);
156         put_uts_ns(nsproxy->uts_ns);
157         nsproxy->uts_ns = ns;
158         return 0;
159 }
160 
161 static struct user_namespace *utsns_owner(struct ns_common *ns)
162 {
163         return to_uts_ns(ns)->user_ns;
164 }
165 
166 const struct proc_ns_operations utsns_operations = {
167         .name           = "uts",
168         .type           = CLONE_NEWUTS,
169         .get            = utsns_get,
170         .put            = utsns_put,
171         .install        = utsns_install,
172         .owner          = utsns_owner,
173 };
174 
175 void __init uts_ns_init(void)
176 {
177         uts_ns_cache = kmem_cache_create_usercopy(
178                         "uts_namespace", sizeof(struct uts_namespace), 0,
179                         SLAB_PANIC|SLAB_ACCOUNT,
180                         offsetof(struct uts_namespace, name),
181                         sizeof_field(struct uts_namespace, name),
182                         NULL);
183 }
184 

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