security/keys/dh.c

   1 /* Crypto operations using stored keys
   2  *
   3  * Copyright (c) 2016, Intel Corporation
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License
   7  * as published by the Free Software Foundation; either version
   8  * 2 of the License, or (at your option) any later version.
   9  */
  10
  11 #include <linux/mpi.h>
  12 #include <linux/slab.h>
  13 #include <linux/uaccess.h>
  14 #include <linux/crypto.h>
  15 #include <crypto/hash.h>
  16 #include <keys/user-type.h>
  17 #include "internal.h"
  18
  19 /*
  20  * Public key or shared secret generation function [RFC2631 sec 2.1.1]
  21  *
  22  * ya = g^xa mod p;
  23  * or
  24  * ZZ = yb^xa mod p;
  25  *
  26  * where xa is the local private key, ya is the local public key, g is
  27  * the generator, p is the prime, yb is the remote public key, and ZZ
  28  * is the shared secret.
  29  *
  30  * Both are the same calculation, so g or yb are the "base" and ya or
  31  * ZZ are the "result".
  32  */
  33 static int do_dh(MPI result, MPI base, MPI xa, MPI p)
  34 {
  35         return mpi_powm(result, base, xa, p);
  36 }
  37
  38 static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
  39 {
  40         struct key *key;
  41         key_ref_t key_ref;
  42         long status;
  43         ssize_t ret;
  44
  45         key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
  46         if (IS_ERR(key_ref)) {
  47                 ret = -ENOKEY;
  48                 goto error;
  49         }
  50
  51         key = key_ref_to_ptr(key_ref);
  52
  53         ret = -EOPNOTSUPP;
  54         if (key->type == &key_type_user) {
  55                 down_read(&key->sem);
  56                 status = key_validate(key);
  57                 if (status == 0) {
  58                         const struct user_key_payload *payload;
  59
  60                         payload = user_key_payload_locked(key);
  61
  62                         if (maxlen == 0) {
  63                                 *mpi = NULL;
  64                                 ret = payload->datalen;
  65                         } else if (payload->datalen <= maxlen) {
  66                                 *mpi = mpi_read_raw_data(payload->data,
  67                                                          payload->datalen);
  68                                 if (*mpi)
  69                                         ret = payload->datalen;
  70                         } else {
  71                                 ret = -EINVAL;
  72                         }
  73                 }
  74                 up_read(&key->sem);
  75         }
  76
  77         key_put(key);
  78 error:
  79         return ret;
  80 }
  81
  82 struct kdf_sdesc {
  83         struct shash_desc shash;
  84         char ctx[];
  85 };
  86
  87 static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
  88 {
  89         struct crypto_shash *tfm;
  90         struct kdf_sdesc *sdesc;
  91         int size;
  92         int err;
  93
  94         /* allocate synchronous hash */
  95         tfm = crypto_alloc_shash(hashname, 0, 0);
  96         if (IS_ERR(tfm)) {
  97                 pr_info("could not allocate digest TFM handle %s\n", hashname);
  98                 return PTR_ERR(tfm);
  99         }
 100
 101         err = -EINVAL;
 102         if (crypto_shash_digestsize(tfm) == 0)
 103                 goto out_free_tfm;
 104
 105         err = -ENOMEM;
 106         size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
 107         sdesc = kmalloc(size, GFP_KERNEL);
 108         if (!sdesc)
 109                 goto out_free_tfm;
 110         sdesc->shash.tfm = tfm;
 111         sdesc->shash.flags = 0x0;
 112
 113         *sdesc_ret = sdesc;
 114
 115         return 0;
 116
 117 out_free_tfm:
 118         crypto_free_shash(tfm);
 119         return err;
 120 }
 121
 122 static void kdf_dealloc(struct kdf_sdesc *sdesc)
 123 {
 124         if (!sdesc)
 125                 return;
 126
 127         if (sdesc->shash.tfm)
 128                 crypto_free_shash(sdesc->shash.tfm);
 129
 130         kzfree(sdesc);
 131 }
 132
 133 /*
 134  * Implementation of the KDF in counter mode according to SP800-108 section 5.1
 135  * as well as SP800-56A section 5.8.1 (Single-step KDF).
 136  *
 137  * SP800-56A:
 138  * The src pointer is defined as Z || other info where Z is the shared secret
 139  * from DH and other info is an arbitrary string (see SP800-56A section
 140  * 5.8.1.2).
 141  */
 142 static int kdf_ctr(struct kdf_sdesc *sdesc, const u8 *src, unsigned int slen,
 143                    u8 *dst, unsigned int dlen)
 144 {
 145         struct shash_desc *desc = &sdesc->shash;
 146         unsigned int h = crypto_shash_digestsize(desc->tfm);
 147         int err = 0;
 148         u8 *dst_orig = dst;
 149         __be32 counter = cpu_to_be32(1);
 150
 151         while (dlen) {
 152                 err = crypto_shash_init(desc);
 153                 if (err)
 154                         goto err;
 155
 156                 err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
 157                 if (err)
 158                         goto err;
 159
 160                 if (src && slen) {
 161                         err = crypto_shash_update(desc, src, slen);
 162                         if (err)
 163                                 goto err;
 164                 }
 165
 166                 if (dlen < h) {
 167                         u8 tmpbuffer[h];
 168
 169                         err = crypto_shash_final(desc, tmpbuffer);
 170                         if (err)
 171                                 goto err;
 172                         memcpy(dst, tmpbuffer, dlen);
 173                         memzero_explicit(tmpbuffer, h);
 174                         return 0;
 175                 } else {
 176                         err = crypto_shash_final(desc, dst);
 177                         if (err)
 178                                 goto err;
 179
 180                         dlen -= h;
 181                         dst += h;
 182                         counter = cpu_to_be32(be32_to_cpu(counter) + 1);
 183                 }
 184         }
 185
 186         return 0;
 187
 188 err:
 189         memzero_explicit(dst_orig, dlen);
 190         return err;
 191 }
 192
 193 static int keyctl_dh_compute_kdf(struct kdf_sdesc *sdesc,
 194                                  char __user *buffer, size_t buflen,
 195                                  uint8_t *kbuf, size_t kbuflen)
 196 {
 197         uint8_t *outbuf = NULL;
 198         int ret;
 199
 200         outbuf = kmalloc(buflen, GFP_KERNEL);
 201         if (!outbuf) {
 202                 ret = -ENOMEM;
 203                 goto err;
 204         }
 205
 206         ret = kdf_ctr(sdesc, kbuf, kbuflen, outbuf, buflen);
 207         if (ret)
 208                 goto err;
 209
 210         ret = buflen;
 211         if (copy_to_user(buffer, outbuf, buflen) != 0)
 212                 ret = -EFAULT;
 213
 214 err:
 215         kzfree(outbuf);
 216         return ret;
 217 }
 218
 219 long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 220                          char __user *buffer, size_t buflen,
 221                          struct keyctl_kdf_params *kdfcopy)
 222 {
 223         long ret;
 224         MPI base, private, prime, result;
 225         unsigned nbytes;
 226         struct keyctl_dh_params pcopy;
 227         uint8_t *kbuf;
 228         ssize_t keylen;
 229         size_t resultlen;
 230         struct kdf_sdesc *sdesc = NULL;
 231
 232         if (!params || (!buffer && buflen)) {
 233                 ret = -EINVAL;
 234                 goto out;
 235         }
 236         if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
 237                 ret = -EFAULT;
 238                 goto out;
 239         }
 240
 241         if (kdfcopy) {
 242                 char *hashname;
 243
 244                 if (buflen > KEYCTL_KDF_MAX_OUTPUT_LEN ||
 245                     kdfcopy->otherinfolen > KEYCTL_KDF_MAX_OI_LEN) {
 246                         ret = -EMSGSIZE;
 247                         goto out;
 248                 }
 249
 250                 /* get KDF name string */
 251                 hashname = strndup_user(kdfcopy->hashname, CRYPTO_MAX_ALG_NAME);
 252                 if (IS_ERR(hashname)) {
 253                         ret = PTR_ERR(hashname);
 254                         goto out;
 255                 }
 256
 257                 /* allocate KDF from the kernel crypto API */
 258                 ret = kdf_alloc(&sdesc, hashname);
 259                 kfree(hashname);
 260                 if (ret)
 261                         goto out;
 262         }
 263
 264         /*
 265          * If the caller requests postprocessing with a KDF, allow an
 266          * arbitrary output buffer size since the KDF ensures proper truncation.
 267          */
 268         keylen = mpi_from_key(pcopy.prime, kdfcopy ? SIZE_MAX : buflen, &prime);
 269         if (keylen < 0 || !prime) {
 270                 /* buflen == 0 may be used to query the required buffer size,
 271                  * which is the prime key length.
 272                  */
 273                 ret = keylen;
 274                 goto out;
 275         }
 276
 277         /* The result is never longer than the prime */
 278         resultlen = keylen;
 279
 280         keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
 281         if (keylen < 0 || !base) {
 282                 ret = keylen;
 283                 goto error1;
 284         }
 285
 286         keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
 287         if (keylen < 0 || !private) {
 288                 ret = keylen;
 289                 goto error2;
 290         }
 291
 292         result = mpi_alloc(0);
 293         if (!result) {
 294                 ret = -ENOMEM;
 295                 goto error3;
 296         }
 297
 298         /* allocate space for DH shared secret and SP800-56A otherinfo */
 299         kbuf = kmalloc(kdfcopy ? (resultlen + kdfcopy->otherinfolen) : resultlen,
 300                        GFP_KERNEL);
 301         if (!kbuf) {
 302                 ret = -ENOMEM;
 303                 goto error4;
 304         }
 305
 306         /*
 307          * Concatenate SP800-56A otherinfo past DH shared secret -- the
 308          * input to the KDF is (DH shared secret || otherinfo)
 309          */
 310         if (kdfcopy &&
 311             copy_from_user(kbuf + resultlen, kdfcopy->otherinfo,
 312                            kdfcopy->otherinfolen) != 0) {
 313                 ret = -EFAULT;
 314                 goto error5;
 315         }
 316
 317         ret = do_dh(result, base, private, prime);
 318         if (ret)
 319                 goto error5;
 320
 321         ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
 322         if (ret != 0)
 323                 goto error5;
 324
 325         if (kdfcopy) {
 326                 ret = keyctl_dh_compute_kdf(sdesc, buffer, buflen, kbuf,
 327                                             resultlen + kdfcopy->otherinfolen);
 328         } else {
 329                 ret = nbytes;
 330                 if (copy_to_user(buffer, kbuf, nbytes) != 0)
 331                         ret = -EFAULT;
 332         }
 333
 334 error5:
 335         kzfree(kbuf);
 336 error4:
 337         mpi_free(result);
 338 error3:
 339         mpi_free(private);
 340 error2:
 341         mpi_free(base);
 342 error1:
 343         mpi_free(prime);
 344 out:
 345         kdf_dealloc(sdesc);
 346         return ret;
 347 }
 348
 349 long keyctl_dh_compute(struct keyctl_dh_params __user *params,
 350                        char __user *buffer, size_t buflen,
 351                        struct keyctl_kdf_params __user *kdf)
 352 {
 353         struct keyctl_kdf_params kdfcopy;
 354
 355         if (!kdf)
 356                 return __keyctl_dh_compute(params, buffer, buflen, NULL);
 357
 358         if (copy_from_user(&kdfcopy, kdf, sizeof(kdfcopy)) != 0)
 359                 return -EFAULT;
 360
 361         return __keyctl_dh_compute(params, buffer, buflen, &kdfcopy);
 362 }