lib/uuid.c

   1 /* Copyright (c) 2008, 2009, 2010, 2011, 2013 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 pthread_mutex_t mutex = PTHREAD_ADAPTIVE_MUTEX_INITIALIZER;
  85     uint64_t copy[2];
  86
  87     uuid_init();
  88
  89     /* Copy out the counter's current value, then increment it. */
  90     xpthread_mutex_lock(&mutex);
  91     copy[0] = counter[0];
  92     copy[1] = counter[1];
  93     if (++counter[1] == 0) {
  94         counter[0]++;
  95     }
  96     xpthread_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     /* Set bits to indicate a random UUID.  See RFC 4122 section 4.4. */
 102     uuid->parts[2] &= ~0xc0000000;
 103     uuid->parts[2] |=  0x80000000;
 104     uuid->parts[1] &= ~0x0000f000;
 105     uuid->parts[1] |=  0x00004000;
 106 }
 107
 108 /* Sets 'uuid' to all-zero-bits. */
 109 void
 110 uuid_zero(struct uuid *uuid)
 111 {
 112     uuid->parts[0] = uuid->parts[1] = uuid->parts[2] = uuid->parts[3] = 0;
 113 }
 114
 115 /* Returns true if 'uuid' is all zero, otherwise false. */
 116 bool
 117 uuid_is_zero(const struct uuid *uuid)
 118 {
 119     return (!uuid->parts[0] && !uuid->parts[1]
 120             && !uuid->parts[2] && !uuid->parts[3]);
 121 }
 122
 123 /* Compares 'a' and 'b'.  Returns a negative value if 'a < b', zero if 'a ==
 124  * b', or positive if 'a > b'.  The ordering is lexicographical order of the
 125  * conventional way of writing out UUIDs as strings. */
 126 int
 127 uuid_compare_3way(const struct uuid *a, const struct uuid *b)
 128 {
 129     if (a->parts[0] != b->parts[0]) {
 130         return a->parts[0] > b->parts[0] ? 1 : -1;
 131     } else if (a->parts[1] != b->parts[1]) {
 132         return a->parts[1] > b->parts[1] ? 1 : -1;
 133     } else if (a->parts[2] != b->parts[2]) {
 134         return a->parts[2] > b->parts[2] ? 1 : -1;
 135     } else if (a->parts[3] != b->parts[3]) {
 136         return a->parts[3] > b->parts[3] ? 1 : -1;
 137     } else {
 138         return 0;
 139     }
 140 }
 141
 142 /* Attempts to convert string 's' into a UUID in 'uuid'.  Returns true if
 143  * successful, which will be the case only if 's' has the exact format
 144  * specified by RFC 4122.  Returns false on failure.  On failure, 'uuid' will
 145  * be set to all-zero-bits. */
 146 bool
 147 uuid_from_string(struct uuid *uuid, const char *s)
 148 {
 149     if (!uuid_from_string_prefix(uuid, s)) {
 150         return false;
 151     } else if (s[UUID_LEN] != '\0') {
 152         uuid_zero(uuid);
 153         return false;
 154     } else {
 155         return true;
 156     }
 157 }
 158
 159 /* Same as uuid_from_string() but s[UUID_LEN] is not required to be a null byte
 160  * to succeed; that is, 's' need only begin with UUID syntax, not consist
 161  * entirely of it. */
 162 bool
 163 uuid_from_string_prefix(struct uuid *uuid, const char *s)
 164 {
 165     /* 0         1         2         3      */
 166     /* 012345678901234567890123456789012345 */
 167     /* ------------------------------------ */
 168     /* 00000000-1111-1111-2222-222233333333 */
 169
 170     bool ok;
 171
 172     uuid->parts[0] = hexits_value(s, 8, &ok);
 173     if (!ok || s[8] != '-') {
 174         goto error;
 175     }
 176
 177     uuid->parts[1] = hexits_value(s + 9, 4, &ok) << 16;
 178     if (!ok || s[13] != '-') {
 179         goto error;
 180     }
 181
 182     uuid->parts[1] += hexits_value(s + 14, 4, &ok);
 183     if (!ok || s[18] != '-') {
 184         goto error;
 185     }
 186
 187     uuid->parts[2] = hexits_value(s + 19, 4, &ok) << 16;
 188     if (!ok || s[23] != '-') {
 189         goto error;
 190     }
 191
 192     uuid->parts[2] += hexits_value(s + 24, 4, &ok);
 193     if (!ok) {
 194         goto error;
 195     }
 196
 197     uuid->parts[3] = hexits_value(s + 28, 8, &ok);
 198     if (!ok) {
 199         goto error;
 200     }
 201     return true;
 202
 203 error:
 204     uuid_zero(uuid);
 205     return false;
 206 }
 207 \f
 208 static void
 209 do_init(void)
 210 {
 211     uint8_t sha1[SHA1_DIGEST_SIZE];
 212     struct sha1_ctx sha1_ctx;
 213     uint8_t random_seed[16];
 214     struct timeval now;
 215     pid_t pid, ppid;
 216     uid_t uid;
 217     gid_t gid;
 218
 219     /* Get seed data. */
 220     get_entropy_or_die(random_seed, sizeof random_seed);
 221     xgettimeofday(&now);
 222     pid = getpid();
 223     ppid = getppid();
 224     uid = getuid();
 225     gid = getgid();
 226
 227     /* Convert seed into key. */
 228     sha1_init(&sha1_ctx);
 229     sha1_update(&sha1_ctx, random_seed, sizeof random_seed);
 230     sha1_update(&sha1_ctx, &pid, sizeof pid);
 231     sha1_update(&sha1_ctx, &ppid, sizeof ppid);
 232     sha1_update(&sha1_ctx, &uid, sizeof uid);
 233     sha1_update(&sha1_ctx, &gid, sizeof gid);
 234     sha1_final(&sha1_ctx, sha1);
 235
 236     /* Generate key. */
 237     BUILD_ASSERT(sizeof sha1 >= 16);
 238     aes128_schedule(&key, sha1);
 239
 240     /* Generate initial counter. */
 241     get_entropy_or_die(counter, sizeof counter);
 242 }