xref: /openbmc/linux/kernel/user_namespace.c (revision 4800cd83)
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 static struct kmem_cache *user_ns_cachep __read_mostly;
16 
17 /*
18  * Create a new user namespace, deriving the creator from the user in the
19  * passed credentials, and replacing that user with the new root user for the
20  * new namespace.
21  *
22  * This is called by copy_creds(), which will finish setting the target task's
23  * credentials.
24  */
25 int create_user_ns(struct cred *new)
26 {
27 	struct user_namespace *ns;
28 	struct user_struct *root_user;
29 	int n;
30 
31 	ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
32 	if (!ns)
33 		return -ENOMEM;
34 
35 	kref_init(&ns->kref);
36 
37 	for (n = 0; n < UIDHASH_SZ; ++n)
38 		INIT_HLIST_HEAD(ns->uidhash_table + n);
39 
40 	/* Alloc new root user.  */
41 	root_user = alloc_uid(ns, 0);
42 	if (!root_user) {
43 		kmem_cache_free(user_ns_cachep, ns);
44 		return -ENOMEM;
45 	}
46 
47 	/* set the new root user in the credentials under preparation */
48 	ns->creator = new->user;
49 	new->user = root_user;
50 	new->uid = new->euid = new->suid = new->fsuid = 0;
51 	new->gid = new->egid = new->sgid = new->fsgid = 0;
52 	put_group_info(new->group_info);
53 	new->group_info = get_group_info(&init_groups);
54 #ifdef CONFIG_KEYS
55 	key_put(new->request_key_auth);
56 	new->request_key_auth = NULL;
57 #endif
58 	/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
59 
60 	/* root_user holds a reference to ns, our reference can be dropped */
61 	put_user_ns(ns);
62 
63 	return 0;
64 }
65 
66 /*
67  * Deferred destructor for a user namespace.  This is required because
68  * free_user_ns() may be called with uidhash_lock held, but we need to call
69  * back to free_uid() which will want to take the lock again.
70  */
71 static void free_user_ns_work(struct work_struct *work)
72 {
73 	struct user_namespace *ns =
74 		container_of(work, struct user_namespace, destroyer);
75 	free_uid(ns->creator);
76 	kmem_cache_free(user_ns_cachep, ns);
77 }
78 
79 void free_user_ns(struct kref *kref)
80 {
81 	struct user_namespace *ns =
82 		container_of(kref, struct user_namespace, kref);
83 
84 	INIT_WORK(&ns->destroyer, free_user_ns_work);
85 	schedule_work(&ns->destroyer);
86 }
87 EXPORT_SYMBOL(free_user_ns);
88 
89 uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
90 {
91 	struct user_namespace *tmp;
92 
93 	if (likely(to == cred->user->user_ns))
94 		return uid;
95 
96 
97 	/* Is cred->user the creator of the target user_ns
98 	 * or the creator of one of it's parents?
99 	 */
100 	for ( tmp = to; tmp != &init_user_ns;
101 	      tmp = tmp->creator->user_ns ) {
102 		if (cred->user == tmp->creator) {
103 			return (uid_t)0;
104 		}
105 	}
106 
107 	/* No useful relationship so no mapping */
108 	return overflowuid;
109 }
110 
111 gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
112 {
113 	struct user_namespace *tmp;
114 
115 	if (likely(to == cred->user->user_ns))
116 		return gid;
117 
118 	/* Is cred->user the creator of the target user_ns
119 	 * or the creator of one of it's parents?
120 	 */
121 	for ( tmp = to; tmp != &init_user_ns;
122 	      tmp = tmp->creator->user_ns ) {
123 		if (cred->user == tmp->creator) {
124 			return (gid_t)0;
125 		}
126 	}
127 
128 	/* No useful relationship so no mapping */
129 	return overflowgid;
130 }
131 
132 static __init int user_namespaces_init(void)
133 {
134 	user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
135 	return 0;
136 }
137 module_init(user_namespaces_init);
138