Add fallback for random number generator

`getrandom()` is available since Linux 3.17 (2014/10/05) yet there are older devices that don't
meet this requirement.

Closes #22691.
PR #22723.

src/base/utils/random.cpp

@@ -42,7 +42,7 @@
 
 uint32_t Utils::Random::rand(const uint32_t min, const uint32_t max)
 {
-    static RandomLayer layer;
+    static const RandomLayer layer;
 
     // new distribution is cheap: https://stackoverflow.com/a/19036349
     std::uniform_int_distribution<uint32_t> uniform(min, max);

src/base/utils/randomlayer_linux.cpp

@@ -27,6 +27,7 @@
  */
 
 #include <cerrno>
+#include <cstdio>
 #include <cstring>
 #include <limits>
 
@@ -44,6 +45,27 @@ namespace
 
         RandomLayer()
         {
+            if (::getrandom(nullptr, 0, 0) < 0)
+            {
+                if (errno == ENOSYS)
+                {
+                    // underlying kernel does not implement this system call
+                    // fallback to `urandom`
+                    m_randDev = fopen("/dev/urandom", "rb");
+                    if (!m_randDev)
+                        qFatal("Failed to open /dev/urandom. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
+                }
+                else
+                {
+                    qFatal("getrandom() error. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
+                }
+            }
+        }
+
+        ~RandomLayer()
+        {
+            if (m_randDev)
+                fclose(m_randDev);
         }
 
         static constexpr result_type min()
@@ -56,7 +78,15 @@ namespace
             return std::numeric_limits<result_type>::max();
         }
 
-        result_type operator()()
+        result_type operator()() const
+        {
+            if (!m_randDev)
+                return getRandomViaAPI();
+            return getRandomViaFile();
+        }
+
+    private:
+        result_type getRandomViaAPI() const
         {
             const int RETRY_MAX = 3;
 
@@ -68,10 +98,21 @@ namespace
                     return buf;
 
                 if (result < 0)
-                    qFatal("getrandom() error. Reason: %s. Error code: %d.", std::strerror(errno), errno);
+                    qFatal("getrandom() error. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
             }
 
             qFatal("getrandom() failed. Reason: too many retries.");
         }
+
+        result_type getRandomViaFile() const
+        {
+            result_type buf = 0;
+            if (fread(&buf, sizeof(buf), 1, m_randDev) == 1)
+                return buf;
+
+            qFatal("Read /dev/urandom error. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
+        }
+
+        FILE *m_randDev = nullptr;
     };
 }

src/base/utils/randomlayer_other.cpp

@@ -46,7 +46,7 @@ namespace
             : m_randDev {fopen("/dev/urandom", "rb")}
         {
             if (!m_randDev)
-                qFatal("Failed to open /dev/urandom. Reason: %s. Error code: %d.", std::strerror(errno), errno);
+                qFatal("Failed to open /dev/urandom. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
         }
 
         ~RandomLayer()
@@ -67,10 +67,10 @@ namespace
         result_type operator()() const
         {
             result_type buf = 0;
-            if (fread(&buf, sizeof(buf), 1, m_randDev) != 1)
+            if (fread(&buf, sizeof(buf), 1, m_randDev) == 1)
-                qFatal("Read /dev/urandom error. Reason: %s. Error code: %d.", std::strerror(errno), errno);
+                return buf;
 
-            return buf;
+            qFatal("Read /dev/urandom error. Reason: \"%s\". Error code: %d.", std::strerror(errno), errno);
         }
 
     private:

src/base/utils/randomlayer_win.cpp

@@ -60,7 +60,7 @@ namespace
             return std::numeric_limits<result_type>::max();
         }
 
-        result_type operator()()
+        result_type operator()() const
         {
             result_type buf = 0;
             const bool result = m_processPrng(reinterpret_cast<PBYTE>(&buf), sizeof(buf));