Root/kernel/user_namespace.c

1/*
2 * This program is free software; you can redistribute it and/or
3 * modify it under the terms of the GNU General Public License as
4 * published by the Free Software Foundation, version 2 of the
5 * License.
6 */
7
8#include <linux/module.h>
9#include <linux/nsproxy.h>
10#include <linux/slab.h>
11#include <linux/user_namespace.h>
12#include <linux/highuid.h>
13#include <linux/cred.h>
14
15/*
16 * Create a new user namespace, deriving the creator from the user in the
17 * passed credentials, and replacing that user with the new root user for the
18 * new namespace.
19 *
20 * This is called by copy_creds(), which will finish setting the target task's
21 * credentials.
22 */
23int create_user_ns(struct cred *new)
24{
25    struct user_namespace *ns;
26    struct user_struct *root_user;
27    int n;
28
29    ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
30    if (!ns)
31        return -ENOMEM;
32
33    kref_init(&ns->kref);
34
35    for (n = 0; n < UIDHASH_SZ; ++n)
36        INIT_HLIST_HEAD(ns->uidhash_table + n);
37
38    /* Alloc new root user. */
39    root_user = alloc_uid(ns, 0);
40    if (!root_user) {
41        kfree(ns);
42        return -ENOMEM;
43    }
44
45    /* set the new root user in the credentials under preparation */
46    ns->creator = new->user;
47    new->user = root_user;
48    new->uid = new->euid = new->suid = new->fsuid = 0;
49    new->gid = new->egid = new->sgid = new->fsgid = 0;
50    put_group_info(new->group_info);
51    new->group_info = get_group_info(&init_groups);
52#ifdef CONFIG_KEYS
53    key_put(new->request_key_auth);
54    new->request_key_auth = NULL;
55#endif
56    /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
57
58    /* root_user holds a reference to ns, our reference can be dropped */
59    put_user_ns(ns);
60
61    return 0;
62}
63
64/*
65 * Deferred destructor for a user namespace. This is required because
66 * free_user_ns() may be called with uidhash_lock held, but we need to call
67 * back to free_uid() which will want to take the lock again.
68 */
69static void free_user_ns_work(struct work_struct *work)
70{
71    struct user_namespace *ns =
72        container_of(work, struct user_namespace, destroyer);
73    free_uid(ns->creator);
74    kfree(ns);
75}
76
77void free_user_ns(struct kref *kref)
78{
79    struct user_namespace *ns =
80        container_of(kref, struct user_namespace, kref);
81
82    INIT_WORK(&ns->destroyer, free_user_ns_work);
83    schedule_work(&ns->destroyer);
84}
85EXPORT_SYMBOL(free_user_ns);
86
87uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
88{
89    struct user_namespace *tmp;
90
91    if (likely(to == cred->user->user_ns))
92        return uid;
93
94
95    /* Is cred->user the creator of the target user_ns
96     * or the creator of one of it's parents?
97     */
98    for ( tmp = to; tmp != &init_user_ns;
99          tmp = tmp->creator->user_ns ) {
100        if (cred->user == tmp->creator) {
101            return (uid_t)0;
102        }
103    }
104
105    /* No useful relationship so no mapping */
106    return overflowuid;
107}
108
109gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
110{
111    struct user_namespace *tmp;
112
113    if (likely(to == cred->user->user_ns))
114        return gid;
115
116    /* Is cred->user the creator of the target user_ns
117     * or the creator of one of it's parents?
118     */
119    for ( tmp = to; tmp != &init_user_ns;
120          tmp = tmp->creator->user_ns ) {
121        if (cred->user == tmp->creator) {
122            return (gid_t)0;
123        }
124    }
125
126    /* No useful relationship so no mapping */
127    return overflowgid;
128}
129

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