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 static struct key_acl request_key_auth_acl = {
  28         .usage  = REFCOUNT_INIT(1),
  29         .nr_ace = 2,
  30         .possessor_viewable = true,
  31         .aces = {
  32                 KEY_POSSESSOR_ACE(KEY_ACE_VIEW | KEY_ACE_READ | KEY_ACE_SEARCH |
  33                                   KEY_ACE_LINK),
  34                 KEY_OWNER_ACE(KEY_ACE_VIEW),
  35         }
  36 };
  37
  38 /*
  39  * The request-key authorisation key type definition.
  40  */
  41 struct key_type key_type_request_key_auth = {
  42         .name           = ".request_key_auth",
  43         .def_datalen    = sizeof(struct request_key_auth),
  44         .preparse       = request_key_auth_preparse,
  45         .free_preparse  = request_key_auth_free_preparse,
  46         .instantiate    = request_key_auth_instantiate,
  47         .describe       = request_key_auth_describe,
  48         .revoke         = request_key_auth_revoke,
  49         .destroy        = request_key_auth_destroy,
  50         .read           = request_key_auth_read,
  51 };
  52
  53 static int request_key_auth_preparse(struct key_preparsed_payload *prep)
  54 {
  55         return 0;
  56 }
  57
  58 static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
  59 {
  60 }
  61
  62 /*
  63  * Instantiate a request-key authorisation key.
  64  */
  65 static int request_key_auth_instantiate(struct key *key,
  66                                         struct key_preparsed_payload *prep)
  67 {
  68         rcu_assign_keypointer(key, (struct request_key_auth *)prep->data);
  69         return 0;
  70 }
  71
  72 /*
  73  * Describe an authorisation token.
  74  */
  75 static void request_key_auth_describe(const struct key *key,
  76                                       struct seq_file *m)
  77 {
  78         struct request_key_auth *rka = dereference_key_rcu(key);
  79
  80         seq_puts(m, "key:");
  81         seq_puts(m, key->description);
  82         if (key_is_positive(key))
  83                 seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
  84 }
  85
  86 /*
  87  * Read the callout_info data (retrieves the callout information).
  88  * - the key's semaphore is read-locked
  89  */
  90 static long request_key_auth_read(const struct key *key,
  91                                   char __user *buffer, size_t buflen)
  92 {
  93         struct request_key_auth *rka = dereference_key_locked(key);
  94         size_t datalen;
  95         long ret;
  96
  97         datalen = rka->callout_len;
  98         ret = datalen;
  99
 100         /* we can return the data as is */
 101         if (buffer && buflen > 0) {
 102                 if (buflen > datalen)
 103                         buflen = datalen;
 104
 105                 if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
 106                         ret = -EFAULT;
 107         }
 108
 109         return ret;
 110 }
 111
 112 static void free_request_key_auth(struct request_key_auth *rka)
 113 {
 114         if (!rka)
 115                 return;
 116         key_put(rka->target_key);
 117         key_put(rka->dest_keyring);
 118         if (rka->cred)
 119                 put_cred(rka->cred);
 120         kfree(rka->callout_info);
 121         kfree(rka);
 122 }
 123
 124 /*
 125  * Dispose of the request_key_auth record under RCU conditions
 126  */
 127 static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
 128 {
 129         struct request_key_auth *rka =
 130                 container_of(rcu, struct request_key_auth, rcu);
 131
 132         free_request_key_auth(rka);
 133 }
 134
 135 /*
 136  * Handle revocation of an authorisation token key.
 137  *
 138  * Called with the key sem write-locked.
 139  */
 140 static void request_key_auth_revoke(struct key *key)
 141 {
 142         struct request_key_auth *rka = dereference_key_locked(key);
 143
 144         kenter("{%d}", key->serial);
 145         rcu_assign_keypointer(key, NULL);
 146         call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
 147 }
 148
 149 /*
 150  * Destroy an instantiation authorisation token key.
 151  */
 152 static void request_key_auth_destroy(struct key *key)
 153 {
 154         struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);
 155
 156         kenter("{%d}", key->serial);
 157         if (rka) {
 158                 rcu_assign_keypointer(key, NULL);
 159                 call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
 160         }
 161 }
 162
 163 /*
 164  * Create an authorisation token for /sbin/request-key or whoever to gain
 165  * access to the caller's security data.
 166  */
 167 struct key *request_key_auth_new(struct key *target, const char *op,
 168                                  const void *callout_info, size_t callout_len,
 169                                  struct key *dest_keyring)
 170 {
 171         struct request_key_auth *rka, *irka;
 172         const struct cred *cred = current_cred();
 173         struct key *authkey = NULL;
 174         char desc[20];
 175         int ret = -ENOMEM;
 176
 177         kenter("%d,", target->serial);
 178
 179         /* allocate a auth record */
 180         rka = kzalloc(sizeof(*rka), GFP_KERNEL);
 181         if (!rka)
 182                 goto error;
 183         rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
 184         if (!rka->callout_info)
 185                 goto error_free_rka;
 186         rka->callout_len = callout_len;
 187         strlcpy(rka->op, op, sizeof(rka->op));
 188
 189         /* see if the calling process is already servicing the key request of
 190          * another process */
 191         if (cred->request_key_auth) {
 192                 /* it is - use that instantiation context here too */
 193                 down_read(&cred->request_key_auth->sem);
 194
 195                 /* if the auth key has been revoked, then the key we're
 196                  * servicing is already instantiated */
 197                 if (test_bit(KEY_FLAG_REVOKED,
 198                              &cred->request_key_auth->flags)) {
 199                         up_read(&cred->request_key_auth->sem);
 200                         ret = -EKEYREVOKED;
 201                         goto error_free_rka;
 202                 }
 203
 204                 irka = cred->request_key_auth->payload.data[0];
 205                 rka->cred = get_cred(irka->cred);
 206                 rka->pid = irka->pid;
 207
 208                 up_read(&cred->request_key_auth->sem);
 209         }
 210         else {
 211                 /* it isn't - use this process as the context */
 212                 rka->cred = get_cred(cred);
 213                 rka->pid = current->pid;
 214         }
 215
 216         rka->target_key = key_get(target);
 217         rka->dest_keyring = key_get(dest_keyring);
 218
 219         /* allocate the auth key */
 220         sprintf(desc, "%x", target->serial);
 221
 222         authkey = key_alloc(&key_type_request_key_auth, desc,
 223                             cred->fsuid, cred->fsgid, cred,
 224                             &request_key_auth_acl,
 225                             KEY_ALLOC_NOT_IN_QUOTA, NULL);
 226         if (IS_ERR(authkey)) {
 227                 ret = PTR_ERR(authkey);
 228                 goto error_free_rka;
 229         }
 230
 231         /* construct the auth key */
 232         ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
 233         if (ret < 0)
 234                 goto error_put_authkey;
 235
 236         kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
 237         return authkey;
 238
 239 error_put_authkey:
 240         key_put(authkey);
 241 error_free_rka:
 242         free_request_key_auth(rka);
 243 error:
 244         kleave("= %d", ret);
 245         return ERR_PTR(ret);
 246 }
 247
 248 /*
 249  * Search the current process's keyrings for the authorisation key for
 250  * instantiation of a key.
 251  */
 252 struct key *key_get_instantiation_authkey(key_serial_t target_id)
 253 {
 254         char description[16];
 255         struct keyring_search_context ctx = {
 256                 .index_key.type         = &key_type_request_key_auth,
 257                 .index_key.description  = description,
 258                 .cred                   = current_cred(),
 259                 .match_data.cmp         = key_default_cmp,
 260                 .match_data.raw_data    = description,
 261                 .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
 262                 .flags                  = (KEYRING_SEARCH_DO_STATE_CHECK |
 263                                            KEYRING_SEARCH_RECURSE),
 264         };
 265         struct key *authkey;
 266         key_ref_t authkey_ref;
 267
 268         ctx.index_key.desc_len = sprintf(description, "%x", target_id);
 269
 270         rcu_read_lock();
 271         authkey_ref = search_process_keyrings_rcu(&ctx);
 272         rcu_read_unlock();
 273
 274         if (IS_ERR(authkey_ref)) {
 275                 authkey = ERR_CAST(authkey_ref);
 276                 if (authkey == ERR_PTR(-EAGAIN))
 277                         authkey = ERR_PTR(-ENOKEY);
 278                 goto error;
 279         }
 280
 281         authkey = key_ref_to_ptr(authkey_ref);
 282         if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
 283                 key_put(authkey);
 284                 authkey = ERR_PTR(-EKEYREVOKED);
 285         }
 286
 287 error:
 288         return authkey;
 289 }