1 /* Tests for the getentropy, getrandom functions.
2    Copyright (C) 2016-2022 Free Software Foundation, Inc.
3    This file is part of the GNU C Library.
4 
5    The GNU C Library is free software; you can redistribute it and/or
6    modify it under the terms of the GNU Lesser General Public
7    License as published by the Free Software Foundation; either
8    version 2.1 of the License, or (at your option) any later version.
9 
10    The GNU C Library is distributed in the hope that it will be useful,
11    but WITHOUT ANY WARRANTY; without even the implied warranty of
12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13    Lesser General Public License for more details.
14 
15    You should have received a copy of the GNU Lesser General Public
16    License along with the GNU C Library; if not, see
17    <https://www.gnu.org/licenses/>.  */
18 
19 #include <errno.h>
20 #include <stdbool.h>
21 #include <stdio.h>
22 #include <string.h>
23 #include <sys/random.h>
24 
25 /* Set to true if any errors are encountered.  */
26 static bool errors;
27 
28 /* Test getrandom with a single buffer length.  NB: The passed-in
29    buffer must have room for four extra bytes after the specified
30    length, which are used to test that getrandom leaves those bytes
31    unchanged.  */
32 static void
test_length(char * buffer,size_t length,unsigned int flags)33 test_length (char *buffer, size_t length, unsigned int flags)
34 {
35   memset (buffer, 0, length);
36   strcpy (buffer + length, "123");
37   ssize_t ret = getrandom (buffer, length, flags);
38   if (ret < 0)
39     {
40       /* EAGAIN is an expected error with GRND_RANDOM and
41          GRND_NONBLOCK.  */
42       if ((flags & GRND_RANDOM)
43           && (flags & GRND_NONBLOCK)
44           && errno == EAGAIN)
45         return;
46       printf ("error: getrandom (%zu, 0x%x): %m\n", length, flags);
47       errors = true;
48       return;
49     }
50  if (ret != length)
51     {
52       if (flags & GRND_RANDOM)
53         {
54           if (ret == 0 || ret > length)
55             {
56               printf ("error: getrandom (%zu, 0x%x) returned %zd\n",
57                       length, flags, ret);
58               errors = true;
59             }
60         }
61       else
62         {
63           printf ("error: getrandom (%zu, 0x%x) returned %zd\n",
64                   length, flags, ret);
65           errors = true;
66         }
67     }
68   if (length >= 7)
69     {
70       /* One spurious test failure in 2**56 is sufficiently
71          unlikely.  */
72       int non_null = 0;
73       for (int i = 0; i < length; ++i)
74         non_null += buffer[i] != 0;
75       if (non_null == 0)
76         {
77           printf ("error: getrandom (%zu, 0x%x) returned all-zero bytes\n",
78                   length, flags);
79           errors = true;
80         }
81     }
82   if (memcmp (buffer + length, "123", 4) != 0)
83     {
84       printf ("error: getrandom (%zu, 0x%x) wrote spurious bytes\n",
85               length, flags);
86       errors = true;
87     }
88 }
89 
90 /* Call getrandom repeatedly to fill the buffer.  */
91 static bool
getrandom_full(char * buffer,size_t length,unsigned int flags)92 getrandom_full (char *buffer, size_t length, unsigned int flags)
93 {
94   char *end = buffer + length;
95   while (buffer < end)
96     {
97       ssize_t ret = getrandom (buffer, end - buffer, flags);
98       if (ret < 0)
99         {
100           printf ("error: getrandom (%zu, 0x%x): %m\n", length, flags);
101           errors = true;
102           return false;
103         }
104       buffer += ret;
105     }
106 
107   return true;
108 }
109 
110 static void
test_flags(unsigned int flags)111 test_flags (unsigned int flags)
112 {
113   /* Test various lengths, but only for !GRND_RANDOM, to conserve
114      entropy.  */
115   {
116     enum { max_length = 300 };
117     char buffer[max_length + 4];
118     if (flags & GRND_RANDOM)
119       test_length (buffer, 0, flags);
120     else
121       {
122         for (int length = 0; length <= 9; ++length)
123           test_length (buffer, length, flags);
124         test_length (buffer, 16, flags);
125         test_length (buffer, max_length, flags);
126       }
127   }
128 
129   /* Test that getrandom returns different data.  */
130   if (!(flags & GRND_NONBLOCK))
131     {
132       char buffer1[8];
133       memset (buffer1, 0, sizeof (buffer1));
134 
135       char buffer2[8];
136       memset (buffer2, 0, sizeof (buffer2));
137 
138       if (getrandom_full (buffer1, sizeof (buffer1), flags)
139           && getrandom_full (buffer2, sizeof (buffer2), flags))
140         {
141           /* The probability that these two 8-byte buffers are equal
142              is very small (assuming that two subsequent calls to
143              getrandom result are independent, uniformly distributed
144              random variables).  */
145           if (memcmp (buffer1, buffer2, sizeof (buffer1)) == 0)
146             {
147               printf ("error: getrandom returns constant value\n");
148               errors = true;
149             }
150         }
151     }
152 }
153 
154 static void
test_getentropy(void)155 test_getentropy (void)
156 {
157   char buf[16];
158   memset (buf, '@', sizeof (buf));
159   if (getentropy (buf, 0) != 0)
160     {
161       printf ("error: getentropy zero length: %m\n");
162       errors = true;
163       return;
164     }
165   for (size_t i = 0; i < sizeof (buf); ++i)
166     if (buf[i] != '@')
167       {
168         printf ("error: getentropy modified zero-length buffer\n");
169         errors = true;
170         return;
171       }
172 
173   if (getentropy (buf, sizeof (buf)) != 0)
174     {
175       printf ("error: getentropy buf: %m\n");
176       errors = true;
177       return;
178     }
179 
180   char buf2[256];
181   _Static_assert (sizeof (buf) < sizeof (buf2), "buf and buf2 compatible");
182   memset (buf2, '@', sizeof (buf2));
183   if (getentropy (buf2, sizeof (buf)) != 0)
184     {
185       printf ("error: getentropy buf2: %m\n");
186       errors = true;
187       return;
188     }
189 
190   /* The probability that these two buffers are equal is very
191      small. */
192   if (memcmp (buf, buf2, sizeof (buf)) == 0)
193     {
194       printf ("error: getentropy appears to return constant bytes\n");
195       errors = true;
196       return;
197     }
198 
199   for (size_t i = sizeof (buf); i < sizeof (buf2); ++i)
200     if (buf2[i] != '@')
201       {
202         printf ("error: getentropy wrote beyond the end of the buffer\n");
203         errors = true;
204         return;
205       }
206 
207   char buf3[257];
208   if (getentropy (buf3, sizeof (buf3)) == 0)
209     {
210       printf ("error: getentropy successful for 257 byte buffer\n");
211       errors = true;
212       return;
213     }
214   if (errno != EIO)
215     {
216       printf ("error: getentropy wrong error for 257 byte buffer: %m\n");
217       errors = true;
218       return;
219     }
220 }
221 
222 static int
do_test(void)223 do_test (void)
224 {
225   /* Check if getrandom is not supported by this system.  */
226   if (getrandom (NULL, 0, 0) == -1 && errno == ENOSYS)
227     return 77;
228 
229   for (int use_random = 0; use_random < 2; ++use_random)
230     for (int use_nonblock = 0; use_nonblock < 2; ++use_nonblock)
231       {
232         unsigned int flags = 0;
233         if (use_random)
234           flags |= GRND_RANDOM;
235         if (use_nonblock)
236           flags |= GRND_NONBLOCK;
237         test_flags (flags);
238       }
239 
240   test_getentropy ();
241 
242   return errors;
243 }
244 
245 #include <support/test-driver.c>
246