SERVER-43641 upgrade random.h

Respecify PseudoRandom and SecureRandom as template instances of
a `mongo::RandomBase<Urbg>` (Urbg is a UniformRandomBitGenerator).
They will only vary in which algorithm they use for their source
bits, and should otherwise support the same exact operations (e.g.
`nextCanonicalDouble`).

Fix range and stats errors in the implementations of those
RandomBase methods, and specify them in terms of the vetted
`<random>` facilities.

Test uniformity of nextInt32(max), which uses an inappropriate
( x % max) operation.  Verify that refactor fixes this issue.

Just keep a shared urandom file descriptor open.

SecureRandom add fill, remove create, fix callers

Obsoletes SERVER-43643 Re: SecureRandom 8kiB buffering

2 files changed, 4 insertions, 23 deletions

diff --git a/src/mongo/crypto/mechanism_scram.h b/src/mongo/crypto/mechanism_scram.h
index fcb16331830..5e0265679ea 100644
--- a/src/mongo/crypto/mechanism_scram.h
+++ b/src/mongo/crypto/mechanism_scram.h
@@ -102,15 +102,9 @@ public:
     }
 
     static std::vector<std::uint8_t> generateSecureRandomSalt() {
-        // Express salt length as a number of quad words, rounded up.
-        constexpr auto qwords = (saltLength() + sizeof(std::int64_t) - 1) / sizeof(std::int64_t);
-        std::array<std::int64_t, qwords> userSalt;
-
-        std::unique_ptr<SecureRandom> sr(SecureRandom::create());
-        std::generate(userSalt.begin(), userSalt.end(), [&sr] { return sr->nextInt64(); });
-        return std::vector<std::uint8_t>(reinterpret_cast<std::uint8_t*>(userSalt.data()),
-                                         reinterpret_cast<std::uint8_t*>(userSalt.data()) +
-                                             saltLength());
+        std::vector<std::uint8_t> salt(saltLength());
+        SecureRandom().fill(salt.data(), salt.size());
+        return salt;
     }
 
 private:
diff --git a/src/mongo/crypto/symmetric_crypto.cpp b/src/mongo/crypto/symmetric_crypto.cpp
index 32d888cfbbb..0a6bbc2e916 100644
--- a/src/mongo/crypto/symmetric_crypto.cpp
+++ b/src/mongo/crypto/symmetric_crypto.cpp
@@ -48,12 +48,7 @@
 namespace mongo {
 namespace crypto {
 
-namespace {
-std::unique_ptr<SecureRandom> random;
-}  // namespace
-
 MONGO_INITIALIZER(CreateKeyEntropySource)(InitializerContext* context) {
-    random = std::unique_ptr<SecureRandom>(SecureRandom::create());
     return Status::OK();
 }
 
@@ -90,16 +85,8 @@ std::string getStringFromCipherMode(aesMode mode) {
 
 SymmetricKey aesGenerate(size_t keySize, SymmetricKeyId keyId) {
     invariant(keySize == sym256KeySize);
-
     SecureVector<uint8_t> key(keySize);
-
-    size_t offset = 0;
-    while (offset < keySize) {
-        std::uint64_t randomValue = random->nextInt64();
-        memcpy(key->data() + offset, &randomValue, sizeof(randomValue));
-        offset += sizeof(randomValue);
-    }
-
+    SecureRandom().fill(key->data(), key->size());
     return SymmetricKey(std::move(key), aesAlgorithm, std::move(keyId));
 }