lib/uuid.c

   1 /* Copyright (c) 2008, 2009, 2010, 2011, 2013, 2016 Nicira, Inc.
   2  *
   3  * Licensed under the Apache License, Version 2.0 (the "License");
   4  * you may not use this file except in compliance with the License.
   5  * You may obtain a copy of the License at:
   6  *
   7  *     http://www.apache.org/licenses/LICENSE-2.0
   8  *
   9  * Unless required by applicable law or agreed to in writing, software
  10  * distributed under the License is distributed on an "AS IS" BASIS,
  11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12  * See the License for the specific language governing permissions and
  13  * limitations under the License.
  14  */
  15
  16 #include <config.h>
  17
  18 #include "uuid.h"
  19
  20 #include <ctype.h>
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <sys/time.h>
  24 #include <sys/types.h>
  25 #include <unistd.h>
  26
  27 #include "aes128.h"
  28 #include "entropy.h"
  29 #include "ovs-thread.h"
  30 #include "sha1.h"
  31 #include "timeval.h"
  32 #include "util.h"
  33
  34 static struct aes128 key;
  35 static uint64_t counter[2];
  36 BUILD_ASSERT_DECL(sizeof counter == 16);
  37
  38 static void do_init(void);
  39
  40 /*
  41  * Initialize the UUID module.  Aborts the program with an error message if
  42  * initialization fails (which should never happen on a properly configured
  43  * machine.)
  44  *
  45  * Currently initialization is only needed by uuid_generate().  uuid_generate()
  46  * will automatically call uuid_init() itself, so it's only necessary to call
  47  * this function explicitly if you want to abort the program earlier than the
  48  * first UUID generation in case of failure.
  49  */
  50 void
  51 uuid_init(void)
  52 {
  53     static pthread_once_t once = PTHREAD_ONCE_INIT;
  54     pthread_once(&once, do_init);
  55 }
  56
  57 /* Generates a new random UUID in 'uuid'.
  58  *
  59  * We go to some trouble to ensure as best we can that the generated UUID has
  60  * these properties:
  61  *
  62  *      - Uniqueness.  The random number generator is seeded using both the
  63  *        system clock and the system random number generator, plus a few
  64  *        other identifiers, which is about as good as we can get in any kind
  65  *        of simple way.
  66  *
  67  *      - Unpredictability.  In some situations it could be bad for an
  68  *        adversary to be able to guess the next UUID to be generated with some
  69  *        probability of success.  This property may or may not be important
  70  *        for our purposes, but it is better if we can get it.
  71  *
  72  * To ensure both of these, we start by taking our seed data and passing it
  73  * through SHA-1.  We use the result as an AES-128 key.  We also generate a
  74  * random 16-byte value[*] which we then use as the counter for CTR mode.  To
  75  * generate a UUID in a manner compliant with the above goals, we merely
  76  * increment the counter and encrypt it.
  77  *
  78  * [*] It is not actually important that the initial value of the counter be
  79  *     random.  AES-128 in counter mode is secure either way.
  80  */
  81 void
  82 uuid_generate(struct uuid *uuid)
  83 {
  84     static struct ovs_mutex mutex = OVS_MUTEX_INITIALIZER;
  85     uint64_t copy[2];
  86
  87     uuid_init();
  88
  89     /* Copy out the counter's current value, then increment it. */
  90     ovs_mutex_lock(&mutex);
  91     copy[0] = counter[0];
  92     copy[1] = counter[1];
  93     if (++counter[1] == 0) {
  94         counter[0]++;
  95     }
  96     ovs_mutex_unlock(&mutex);
  97
  98     /* AES output is exactly 16 bytes, so we encrypt directly into 'uuid'. */
  99     aes128_encrypt(&key, copy, uuid);
 100
 101     uuid_set_bits_v4(uuid);
 102 }
 103
 104 void
 105 uuid_set_bits_v4(struct uuid *uuid)
 106 {
 107     /* Set bits to indicate a random UUID.  See RFC 4122 section 4.4. */
 108     uuid->parts[2] &= ~0xc0000000;
 109     uuid->parts[2] |=  0x80000000;
 110     uuid->parts[1] &= ~0x0000f000;
 111     uuid->parts[1] |=  0x00004000;
 112 }
 113
 114 /* Sets 'uuid' to all-zero-bits. */
 115 void
 116 uuid_zero(struct uuid *uuid)
 117 {
 118     *uuid = UUID_ZERO;
 119 }
 120
 121 /* Returns true if 'uuid' is all zero, otherwise false. */
 122 bool
 123 uuid_is_zero(const struct uuid *uuid)
 124 {
 125     return (!uuid->parts[0] && !uuid->parts[1]
 126             && !uuid->parts[2] && !uuid->parts[3]);
 127 }
 128
 129 /* Compares 'a' and 'b'.  Returns a negative value if 'a < b', zero if 'a ==
 130  * b', or positive if 'a > b'.  The ordering is lexicographical order of the
 131  * conventional way of writing out UUIDs as strings. */
 132 int
 133 uuid_compare_3way(const struct uuid *a, const struct uuid *b)
 134 {
 135     if (a->parts[0] != b->parts[0]) {
 136         return a->parts[0] > b->parts[0] ? 1 : -1;
 137     } else if (a->parts[1] != b->parts[1]) {
 138         return a->parts[1] > b->parts[1] ? 1 : -1;
 139     } else if (a->parts[2] != b->parts[2]) {
 140         return a->parts[2] > b->parts[2] ? 1 : -1;
 141     } else if (a->parts[3] != b->parts[3]) {
 142         return a->parts[3] > b->parts[3] ? 1 : -1;
 143     } else {
 144         return 0;
 145     }
 146 }
 147
 148 /* Attempts to convert string 's' into a UUID in 'uuid'.  Returns true if
 149  * successful, which will be the case only if 's' has the exact format
 150  * specified by RFC 4122.  Returns false on failure.  On failure, 'uuid' will
 151  * be set to all-zero-bits. */
 152 bool
 153 uuid_from_string(struct uuid *uuid, const char *s)
 154 {
 155     if (!uuid_from_string_prefix(uuid, s)) {
 156         return false;
 157     } else if (s[UUID_LEN] != '\0') {
 158         uuid_zero(uuid);
 159         return false;
 160     } else {
 161         return true;
 162     }
 163 }
 164
 165 /* Same as uuid_from_string() but s[UUID_LEN] is not required to be a null byte
 166  * to succeed; that is, 's' need only begin with UUID syntax, not consist
 167  * entirely of it. */
 168 bool
 169 uuid_from_string_prefix(struct uuid *uuid, const char *s)
 170 {
 171     /* 0         1         2         3      */
 172     /* 012345678901234567890123456789012345 */
 173     /* ------------------------------------ */
 174     /* 00000000-1111-1111-2222-222233333333 */
 175
 176     bool ok;
 177
 178     uuid->parts[0] = hexits_value(s, 8, &ok);
 179     if (!ok || s[8] != '-') {
 180         goto error;
 181     }
 182
 183     uuid->parts[1] = hexits_value(s + 9, 4, &ok) << 16;
 184     if (!ok || s[13] != '-') {
 185         goto error;
 186     }
 187
 188     uuid->parts[1] += hexits_value(s + 14, 4, &ok);
 189     if (!ok || s[18] != '-') {
 190         goto error;
 191     }
 192
 193     uuid->parts[2] = hexits_value(s + 19, 4, &ok) << 16;
 194     if (!ok || s[23] != '-') {
 195         goto error;
 196     }
 197
 198     uuid->parts[2] += hexits_value(s + 24, 4, &ok);
 199     if (!ok) {
 200         goto error;
 201     }
 202
 203     uuid->parts[3] = hexits_value(s + 28, 8, &ok);
 204     if (!ok) {
 205         goto error;
 206     }
 207     return true;
 208
 209 error:
 210     uuid_zero(uuid);
 211     return false;
 212 }
 213
 214 /* Returns the number of characters at the beginning of 's' that are valid for
 215  * a UUID.  For example, the "123" at the beginning of "123xyzzy" could begin a
 216  * UUID, so uuid_is_partial_string() would return 3; for "xyzzy", this function
 217  * would return 0, since "x" can't start a UUID. */
 218 int
 219 uuid_is_partial_string(const char *s)
 220 {
 221     static const char tmpl[UUID_LEN] = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
 222     size_t i;
 223     for (i = 0; i < UUID_LEN; i++) {
 224         if (tmpl[i] == 'x'
 225             ? hexit_value(s[i]) < 0
 226             : s[i] != '-') {
 227             break;
 228         }
 229     }
 230     return i;
 231 }
 232
 233 \f
 234 static void
 235 sha1_update_int(struct sha1_ctx *sha1_ctx, uintmax_t x)
 236 {
 237    sha1_update(sha1_ctx, &x, sizeof x);
 238 }
 239
 240 static void
 241 do_init(void)
 242 {
 243     uint8_t sha1[SHA1_DIGEST_SIZE];
 244     struct sha1_ctx sha1_ctx;
 245     uint8_t random_seed[16];
 246     struct timeval now;
 247
 248     /* Get seed data. */
 249     get_entropy_or_die(random_seed, sizeof random_seed);
 250     xgettimeofday(&now);
 251
 252     /* Convert seed into key. */
 253     sha1_init(&sha1_ctx);
 254     sha1_update(&sha1_ctx, random_seed, sizeof random_seed);
 255     sha1_update(&sha1_ctx, &now, sizeof now);
 256     sha1_update_int(&sha1_ctx, getpid());
 257 #ifndef _WIN32
 258     sha1_update_int(&sha1_ctx, getppid());
 259     sha1_update_int(&sha1_ctx, getuid());
 260     sha1_update_int(&sha1_ctx, getgid());
 261 #endif
 262     sha1_final(&sha1_ctx, sha1);
 263
 264     /* Generate key. */
 265     BUILD_ASSERT(sizeof sha1 >= 16);
 266     aes128_schedule(&key, sha1);
 267
 268     /* Generate initial counter. */
 269     get_entropy_or_die(counter, sizeof counter);
 270 }