keys: Fix missing null pointer check in request_key_auth_describe()
[sfrench/cifs-2.6.git] / security / keys / request_key_auth.c
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Request key authorisation token key definition.
3  *
4  * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
5  * Written by David Howells (dhowells@redhat.com)
6  *
7  * See Documentation/security/keys/request-key.rst
8  */
9
10 #include <linux/sched.h>
11 #include <linux/err.h>
12 #include <linux/seq_file.h>
13 #include <linux/slab.h>
14 #include <linux/uaccess.h>
15 #include "internal.h"
16 #include <keys/request_key_auth-type.h>
17
18 static int request_key_auth_preparse(struct key_preparsed_payload *);
19 static void request_key_auth_free_preparse(struct key_preparsed_payload *);
20 static int request_key_auth_instantiate(struct key *,
21                                         struct key_preparsed_payload *);
22 static void request_key_auth_describe(const struct key *, struct seq_file *);
23 static void request_key_auth_revoke(struct key *);
24 static void request_key_auth_destroy(struct key *);
25 static long request_key_auth_read(const struct key *, char __user *, size_t);
26
27 /*
28  * The request-key authorisation key type definition.
29  */
30 struct key_type key_type_request_key_auth = {
31         .name           = ".request_key_auth",
32         .def_datalen    = sizeof(struct request_key_auth),
33         .preparse       = request_key_auth_preparse,
34         .free_preparse  = request_key_auth_free_preparse,
35         .instantiate    = request_key_auth_instantiate,
36         .describe       = request_key_auth_describe,
37         .revoke         = request_key_auth_revoke,
38         .destroy        = request_key_auth_destroy,
39         .read           = request_key_auth_read,
40 };
41
42 static int request_key_auth_preparse(struct key_preparsed_payload *prep)
43 {
44         return 0;
45 }
46
47 static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
48 {
49 }
50
51 /*
52  * Instantiate a request-key authorisation key.
53  */
54 static int request_key_auth_instantiate(struct key *key,
55                                         struct key_preparsed_payload *prep)
56 {
57         rcu_assign_keypointer(key, (struct request_key_auth *)prep->data);
58         return 0;
59 }
60
61 /*
62  * Describe an authorisation token.
63  */
64 static void request_key_auth_describe(const struct key *key,
65                                       struct seq_file *m)
66 {
67         struct request_key_auth *rka = dereference_key_rcu(key);
68
69         if (!rka)
70                 return;
71
72         seq_puts(m, "key:");
73         seq_puts(m, key->description);
74         if (key_is_positive(key))
75                 seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
76 }
77
78 /*
79  * Read the callout_info data (retrieves the callout information).
80  * - the key's semaphore is read-locked
81  */
82 static long request_key_auth_read(const struct key *key,
83                                   char __user *buffer, size_t buflen)
84 {
85         struct request_key_auth *rka = dereference_key_locked(key);
86         size_t datalen;
87         long ret;
88
89         if (!rka)
90                 return -EKEYREVOKED;
91
92         datalen = rka->callout_len;
93         ret = datalen;
94
95         /* we can return the data as is */
96         if (buffer && buflen > 0) {
97                 if (buflen > datalen)
98                         buflen = datalen;
99
100                 if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
101                         ret = -EFAULT;
102         }
103
104         return ret;
105 }
106
107 static void free_request_key_auth(struct request_key_auth *rka)
108 {
109         if (!rka)
110                 return;
111         key_put(rka->target_key);
112         key_put(rka->dest_keyring);
113         if (rka->cred)
114                 put_cred(rka->cred);
115         kfree(rka->callout_info);
116         kfree(rka);
117 }
118
119 /*
120  * Dispose of the request_key_auth record under RCU conditions
121  */
122 static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
123 {
124         struct request_key_auth *rka =
125                 container_of(rcu, struct request_key_auth, rcu);
126
127         free_request_key_auth(rka);
128 }
129
130 /*
131  * Handle revocation of an authorisation token key.
132  *
133  * Called with the key sem write-locked.
134  */
135 static void request_key_auth_revoke(struct key *key)
136 {
137         struct request_key_auth *rka = dereference_key_locked(key);
138
139         kenter("{%d}", key->serial);
140         rcu_assign_keypointer(key, NULL);
141         call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
142 }
143
144 /*
145  * Destroy an instantiation authorisation token key.
146  */
147 static void request_key_auth_destroy(struct key *key)
148 {
149         struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);
150
151         kenter("{%d}", key->serial);
152         if (rka) {
153                 rcu_assign_keypointer(key, NULL);
154                 call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
155         }
156 }
157
158 /*
159  * Create an authorisation token for /sbin/request-key or whoever to gain
160  * access to the caller's security data.
161  */
162 struct key *request_key_auth_new(struct key *target, const char *op,
163                                  const void *callout_info, size_t callout_len,
164                                  struct key *dest_keyring)
165 {
166         struct request_key_auth *rka, *irka;
167         const struct cred *cred = current_cred();
168         struct key *authkey = NULL;
169         char desc[20];
170         int ret = -ENOMEM;
171
172         kenter("%d,", target->serial);
173
174         /* allocate a auth record */
175         rka = kzalloc(sizeof(*rka), GFP_KERNEL);
176         if (!rka)
177                 goto error;
178         rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
179         if (!rka->callout_info)
180                 goto error_free_rka;
181         rka->callout_len = callout_len;
182         strlcpy(rka->op, op, sizeof(rka->op));
183
184         /* see if the calling process is already servicing the key request of
185          * another process */
186         if (cred->request_key_auth) {
187                 /* it is - use that instantiation context here too */
188                 down_read(&cred->request_key_auth->sem);
189
190                 /* if the auth key has been revoked, then the key we're
191                  * servicing is already instantiated */
192                 if (test_bit(KEY_FLAG_REVOKED,
193                              &cred->request_key_auth->flags)) {
194                         up_read(&cred->request_key_auth->sem);
195                         ret = -EKEYREVOKED;
196                         goto error_free_rka;
197                 }
198
199                 irka = cred->request_key_auth->payload.data[0];
200                 rka->cred = get_cred(irka->cred);
201                 rka->pid = irka->pid;
202
203                 up_read(&cred->request_key_auth->sem);
204         }
205         else {
206                 /* it isn't - use this process as the context */
207                 rka->cred = get_cred(cred);
208                 rka->pid = current->pid;
209         }
210
211         rka->target_key = key_get(target);
212         rka->dest_keyring = key_get(dest_keyring);
213
214         /* allocate the auth key */
215         sprintf(desc, "%x", target->serial);
216
217         authkey = key_alloc(&key_type_request_key_auth, desc,
218                             cred->fsuid, cred->fsgid, cred,
219                             KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | KEY_POS_LINK |
220                             KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
221         if (IS_ERR(authkey)) {
222                 ret = PTR_ERR(authkey);
223                 goto error_free_rka;
224         }
225
226         /* construct the auth key */
227         ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
228         if (ret < 0)
229                 goto error_put_authkey;
230
231         kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
232         return authkey;
233
234 error_put_authkey:
235         key_put(authkey);
236 error_free_rka:
237         free_request_key_auth(rka);
238 error:
239         kleave("= %d", ret);
240         return ERR_PTR(ret);
241 }
242
243 /*
244  * Search the current process's keyrings for the authorisation key for
245  * instantiation of a key.
246  */
247 struct key *key_get_instantiation_authkey(key_serial_t target_id)
248 {
249         char description[16];
250         struct keyring_search_context ctx = {
251                 .index_key.type         = &key_type_request_key_auth,
252                 .index_key.description  = description,
253                 .cred                   = current_cred(),
254                 .match_data.cmp         = key_default_cmp,
255                 .match_data.raw_data    = description,
256                 .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
257                 .flags                  = (KEYRING_SEARCH_DO_STATE_CHECK |
258                                            KEYRING_SEARCH_RECURSE),
259         };
260         struct key *authkey;
261         key_ref_t authkey_ref;
262
263         ctx.index_key.desc_len = sprintf(description, "%x", target_id);
264
265         rcu_read_lock();
266         authkey_ref = search_process_keyrings_rcu(&ctx);
267         rcu_read_unlock();
268
269         if (IS_ERR(authkey_ref)) {
270                 authkey = ERR_CAST(authkey_ref);
271                 if (authkey == ERR_PTR(-EAGAIN))
272                         authkey = ERR_PTR(-ENOKEY);
273                 goto error;
274         }
275
276         authkey = key_ref_to_ptr(authkey_ref);
277         if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
278                 key_put(authkey);
279                 authkey = ERR_PTR(-EKEYREVOKED);
280         }
281
282 error:
283         return authkey;
284 }