1 /* Copyright (c) 2020, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/ctrdrbg.h>
16
17 #include "../fipsmodule/rand/internal.h"
18 #include "../internal.h"
19
20 #if defined(BORINGSSL_FIPS)
21
22 #define ENTROPY_READ_LEN \
23 (/* last_block size */ 16 + CTR_DRBG_ENTROPY_LEN * BORINGSSL_FIPS_OVERREAD)
24
25 #if defined(OPENSSL_ANDROID)
26
27 #include <errno.h>
28 #include <stdatomic.h>
29 #include <sys/socket.h>
30 #include <sys/types.h>
31 #include <sys/un.h>
32 #include <unistd.h>
33
34 // socket_history_t enumerates whether the entropy daemon should be contacted
35 // for a given entropy request. Values other than socket_not_yet_attempted are
36 // sticky so if the first attempt to read from the daemon fails it's assumed
37 // that the daemon is not present and no more attempts will be made. If the
38 // first attempt is successful then attempts will be made forever more.
39 enum socket_history_t {
40 // initial value, no connections to the entropy daemon have been made yet.
41 socket_not_yet_attempted = 0,
42 // reading from the entropy daemon was successful
43 socket_success,
44 // reading from the entropy daemon failed.
45 socket_failed,
46 };
47
48 static _Atomic enum socket_history_t g_socket_history =
49 socket_not_yet_attempted;
50
51 // DAEMON_RESPONSE_LEN is the number of bytes that the entropy daemon replies
52 // with.
53 #define DAEMON_RESPONSE_LEN 496
54
55 static_assert(ENTROPY_READ_LEN == DAEMON_RESPONSE_LEN,
56 "entropy daemon response length mismatch");
57
get_seed_from_daemon(uint8_t * out_entropy,size_t out_entropy_len)58 static int get_seed_from_daemon(uint8_t *out_entropy, size_t out_entropy_len) {
59 // |RAND_need_entropy| should never call this function for more than
60 // |DAEMON_RESPONSE_LEN| bytes.
61 if (out_entropy_len > DAEMON_RESPONSE_LEN) {
62 abort();
63 }
64
65 const enum socket_history_t socket_history = atomic_load(&g_socket_history);
66 if (socket_history == socket_failed) {
67 return 0;
68 }
69
70 int ret = 0;
71 const int sock = socket(AF_UNIX, SOCK_STREAM, 0);
72 if (sock < 0) {
73 goto out;
74 }
75
76 struct sockaddr_un sun;
77 memset(&sun, 0, sizeof(sun));
78 sun.sun_family = AF_UNIX;
79 static const char kSocketPath[] = "/dev/socket/prng_seeder";
80 static_assert(sizeof(kSocketPath) <= UNIX_PATH_MAX,
81 "kSocketPath too long");
82 OPENSSL_memcpy(sun.sun_path, kSocketPath, sizeof(kSocketPath));
83
84 if (connect(sock, (struct sockaddr *)&sun, sizeof(sun))) {
85 goto out;
86 }
87
88 uint8_t buffer[DAEMON_RESPONSE_LEN];
89 size_t done = 0;
90 while (done < sizeof(buffer)) {
91 ssize_t n;
92 do {
93 n = read(sock, buffer + done, sizeof(buffer) - done);
94 } while (n == -1 && errno == EINTR);
95
96 if (n < 1) {
97 goto out;
98 }
99 done += n;
100 }
101
102 if (done != DAEMON_RESPONSE_LEN) {
103 // The daemon should always write |DAEMON_RESPONSE_LEN| bytes on every
104 // connection.
105 goto out;
106 }
107
108 assert(out_entropy_len <= DAEMON_RESPONSE_LEN);
109 OPENSSL_memcpy(out_entropy, buffer, out_entropy_len);
110 ret = 1;
111
112 out:
113 if (socket_history == socket_not_yet_attempted) {
114 enum socket_history_t expected = socket_history;
115 // If another thread has already updated |g_socket_history| then we defer
116 // to their value.
117 atomic_compare_exchange_strong(&g_socket_history, &expected,
118 (ret == 0) ? socket_failed : socket_success);
119 }
120
121 close(sock);
122 return ret;
123 }
124
125 #else
126
get_seed_from_daemon(uint8_t * out_entropy,size_t out_entropy_len)127 static int get_seed_from_daemon(uint8_t *out_entropy, size_t out_entropy_len) {
128 return 0;
129 }
130
131 #endif // OPENSSL_ANDROID
132
133 // RAND_need_entropy is called by the FIPS module when it has blocked because of
134 // a lack of entropy. This signal is used as an indication to feed it more.
RAND_need_entropy(size_t bytes_needed)135 void RAND_need_entropy(size_t bytes_needed) {
136 uint8_t buf[ENTROPY_READ_LEN];
137 size_t todo = sizeof(buf);
138 if (todo > bytes_needed) {
139 todo = bytes_needed;
140 }
141
142 int want_additional_input;
143 if (get_seed_from_daemon(buf, todo)) {
144 want_additional_input = 1;
145 } else {
146 CRYPTO_get_seed_entropy(buf, todo, &want_additional_input);
147 }
148
149 if (boringssl_fips_break_test("CRNG")) {
150 // This breaks the "continuous random number generator test" defined in FIPS
151 // 140-2, section 4.9.2, and implemented in |rand_get_seed|.
152 OPENSSL_memset(buf, 0, todo);
153 }
154
155 RAND_load_entropy(buf, todo, want_additional_input);
156 }
157
158 #endif // FIPS
159