sanity: Move OS random to sanity check function

Move the OS random test to a sanity check function that is called every
time bitcoind is initialized.

Keep `src/test/random_tests.cpp` for the case that later random tests
are added, and keep a rudimentary test that just calls the sanity check.

Author: laanwj

src/init.cpp

@@ -687,9 +687,15 @@ bool InitSanityCheck(void)
         InitError("Elliptic curve cryptography sanity check failure. Aborting.");
         return false;
     }
+
     if (!glibc_sanity_test() || !glibcxx_sanity_test())
         return false;
 
+    if (!Random_SanityCheck()) {
+        InitError("OS cryptographic RNG sanity check failure. Aborting.");
+        return false;
+    }
+
     return true;
 }
 

src/random.cpp

@@ -239,3 +239,33 @@ FastRandomContext::FastRandomContext(bool fDeterministic)
     }
 }
 
+bool Random_SanityCheck()
+{
+    /* This does not measure the quality of randomness, but it does test that
+     * OSRandom() overwrites all 32 bytes of the output given a maximum
+     * number of tries.
+     */
+    static const ssize_t MAX_TRIES = 1024;
+    uint8_t data[NUM_OS_RANDOM_BYTES];
+    bool overwritten[NUM_OS_RANDOM_BYTES] = {}; /* Tracks which bytes have been overwritten at least once */
+    int num_overwritten;
+    int tries = 0;
+    /* Loop until all bytes have been overwritten at least once, or max number tries reached */
+    do {
+        memset(data, 0, NUM_OS_RANDOM_BYTES);
+        GetOSRand(data);
+        for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
+            overwritten[x] |= (data[x] != 0);
+        }
+
+        num_overwritten = 0;
+        for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
+            if (overwritten[x]) {
+                num_overwritten += 1;
+            }
+        }
+
+        tries += 1;
+    } while (num_overwritten < NUM_OS_RANDOM_BYTES && tries < MAX_TRIES);
+    return (num_overwritten == NUM_OS_RANDOM_BYTES); /* If this failed, bailed out after too many tries */
+}

src/random.h

@@ -58,4 +58,9 @@ static const ssize_t NUM_OS_RANDOM_BYTES = 32;
  */
 void GetOSRand(unsigned char *ent32);
 
+/** Check that OS randomness is available and returning the requested number
+ * of bytes.
+ */
+bool Random_SanityCheck();
+
 #endif // BITCOIN_RANDOM_H

src/test/random_tests.cpp

@@ -10,36 +10,9 @@
 
 BOOST_FIXTURE_TEST_SUITE(random_tests, BasicTestingSetup)
 
-static const ssize_t MAX_TRIES = 1024;
-
 BOOST_AUTO_TEST_CASE(osrandom_tests)
 {
-    /* This does not measure the quality of randomness, but it does test that
-     * OSRandom() overwrites all 32 bytes of the output given a maximum
-     * number of tries.
-     */
-    uint8_t data[NUM_OS_RANDOM_BYTES];
-    bool overwritten[NUM_OS_RANDOM_BYTES] = {}; /* Tracks which bytes have been overwritten at least once */
-    int num_overwritten;
-    int tries = 0;
-    /* Loop until all bytes have been overwritten at least once */
-    do {
-        memset(data, 0, NUM_OS_RANDOM_BYTES);
-        GetOSRand(data);
-        for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
-            overwritten[x] |= (data[x] != 0);
-        }
-
-        num_overwritten = 0;
-        for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
-            if (overwritten[x]) {
-                num_overwritten += 1;
-            }
-        }
-
-        tries += 1;
-    } while (num_overwritten < NUM_OS_RANDOM_BYTES && tries < MAX_TRIES);
-    BOOST_CHECK(num_overwritten == NUM_OS_RANDOM_BYTES); /* If this failed, bailed out after too many tries */
+    BOOST_CHECK(Random_SanityCheck());
 }
 
 BOOST_AUTO_TEST_SUITE_END()