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 *, 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 *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                 memcpy(buffer, rka->callout_info, buflen);
 101         }
 102
 103         return ret;
 104 }
 105
 106 static void free_request_key_auth(struct request_key_auth *rka)
 107 {
 108         if (!rka)
 109                 return;
 110         key_put(rka->target_key);
 111         key_put(rka->dest_keyring);
 112         if (rka->cred)
 113                 put_cred(rka->cred);
 114         kfree(rka->callout_info);
 115         kfree(rka);
 116 }
 117
 118 /*
 119  * Dispose of the request_key_auth record under RCU conditions
 120  */
 121 static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
 122 {
 123         struct request_key_auth *rka =
 124                 container_of(rcu, struct request_key_auth, rcu);
 125
 126         free_request_key_auth(rka);
 127 }
 128
 129 /*
 130  * Handle revocation of an authorisation token key.
 131  *
 132  * Called with the key sem write-locked.
 133  */
 134 static void request_key_auth_revoke(struct key *key)
 135 {
 136         struct request_key_auth *rka = dereference_key_locked(key);
 137
 138         kenter("{%d}", key->serial);
 139         rcu_assign_keypointer(key, NULL);
 140         call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
 141 }
 142
 143 /*
 144  * Destroy an instantiation authorisation token key.
 145  */
 146 static void request_key_auth_destroy(struct key *key)
 147 {
 148         struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);
 149
 150         kenter("{%d}", key->serial);
 151         if (rka) {
 152                 rcu_assign_keypointer(key, NULL);
 153                 call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
 154         }
 155 }
 156
 157 /*
 158  * Create an authorisation token for /sbin/request-key or whoever to gain
 159  * access to the caller's security data.
 160  */
 161 struct key *request_key_auth_new(struct key *target, const char *op,
 162                                  const void *callout_info, size_t callout_len,
 163                                  struct key *dest_keyring)
 164 {
 165         struct request_key_auth *rka, *irka;
 166         const struct cred *cred = current_cred();
 167         struct key *authkey = NULL;
 168         char desc[20];
 169         int ret = -ENOMEM;
 170
 171         kenter("%d,", target->serial);
 172
 173         /* allocate a auth record */
 174         rka = kzalloc(sizeof(*rka), GFP_KERNEL);
 175         if (!rka)
 176                 goto error;
 177         rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
 178         if (!rka->callout_info)
 179                 goto error_free_rka;
 180         rka->callout_len = callout_len;
 181         strlcpy(rka->op, op, sizeof(rka->op));
 182
 183         /* see if the calling process is already servicing the key request of
 184          * another process */
 185         if (cred->request_key_auth) {
 186                 /* it is - use that instantiation context here too */
 187                 down_read(&cred->request_key_auth->sem);
 188
 189                 /* if the auth key has been revoked, then the key we're
 190                  * servicing is already instantiated */
 191                 if (test_bit(KEY_FLAG_REVOKED,
 192                              &cred->request_key_auth->flags)) {
 193                         up_read(&cred->request_key_auth->sem);
 194                         ret = -EKEYREVOKED;
 195                         goto error_free_rka;
 196                 }
 197
 198                 irka = cred->request_key_auth->payload.data[0];
 199                 rka->cred = get_cred(irka->cred);
 200                 rka->pid = irka->pid;
 201
 202                 up_read(&cred->request_key_auth->sem);
 203         }
 204         else {
 205                 /* it isn't - use this process as the context */
 206                 rka->cred = get_cred(cred);
 207                 rka->pid = current->pid;
 208         }
 209
 210         rka->target_key = key_get(target);
 211         rka->dest_keyring = key_get(dest_keyring);
 212
 213         /* allocate the auth key */
 214         sprintf(desc, "%x", target->serial);
 215
 216         authkey = key_alloc(&key_type_request_key_auth, desc,
 217                             cred->fsuid, cred->fsgid, cred,
 218                             KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | KEY_POS_LINK |
 219                             KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
 220         if (IS_ERR(authkey)) {
 221                 ret = PTR_ERR(authkey);
 222                 goto error_free_rka;
 223         }
 224
 225         /* construct the auth key */
 226         ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
 227         if (ret < 0)
 228                 goto error_put_authkey;
 229
 230         kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
 231         return authkey;
 232
 233 error_put_authkey:
 234         key_put(authkey);
 235 error_free_rka:
 236         free_request_key_auth(rka);
 237 error:
 238         kleave("= %d", ret);
 239         return ERR_PTR(ret);
 240 }
 241
 242 /*
 243  * Search the current process's keyrings for the authorisation key for
 244  * instantiation of a key.
 245  */
 246 struct key *key_get_instantiation_authkey(key_serial_t target_id)
 247 {
 248         char description[16];
 249         struct keyring_search_context ctx = {
 250                 .index_key.type         = &key_type_request_key_auth,
 251                 .index_key.description  = description,
 252                 .cred                   = current_cred(),
 253                 .match_data.cmp         = key_default_cmp,
 254                 .match_data.raw_data    = description,
 255                 .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
 256                 .flags                  = (KEYRING_SEARCH_DO_STATE_CHECK |
 257                                            KEYRING_SEARCH_RECURSE),
 258         };
 259         struct key *authkey;
 260         key_ref_t authkey_ref;
 261
 262         ctx.index_key.desc_len = sprintf(description, "%x", target_id);
 263
 264         rcu_read_lock();
 265         authkey_ref = search_process_keyrings_rcu(&ctx);
 266         rcu_read_unlock();
 267
 268         if (IS_ERR(authkey_ref)) {
 269                 authkey = ERR_CAST(authkey_ref);
 270                 if (authkey == ERR_PTR(-EAGAIN))
 271                         authkey = ERR_PTR(-ENOKEY);
 272                 goto error;
 273         }
 274
 275         authkey = key_ref_to_ptr(authkey_ref);
 276         if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
 277                 key_put(authkey);
 278                 authkey = ERR_PTR(-EKEYREVOKED);
 279         }
 280
 281 error:
 282         return authkey;
 283 }