From a4c5f03beedf04fcca0ba6fd354d27e66bb3fcf6 Mon Sep 17 00:00:00 2001
From: Mounir IDRASSI <mounir.idrassi@idrix.fr>
Date: Sun, 21 Jun 2020 17:37:11 +0200
Subject: Linux/MacOSX: Read at least 32 bytes from /dev/random before allowing
 it to fail gracefully

---
 src/Core/RandomNumberGenerator.cpp | 13 ++++++++++---
 src/Core/RandomNumberGenerator.h   |  1 +
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/Core/RandomNumberGenerator.cpp b/src/Core/RandomNumberGenerator.cpp
index 6ad46605..38a228ee 100644
--- a/src/Core/RandomNumberGenerator.cpp
+++ b/src/Core/RandomNumberGenerator.cpp
@@ -44,12 +44,12 @@ namespace VeraCrypt
 			throw_sys_sub_if (random == -1, L"/dev/random");
 			finally_do_arg (int, random, { close (finally_arg); });
 
-			// ensure that we have read /dev/random successfully at least once before continuing
+			// ensure that we have read at least 32 bytes from /dev/random before allowing it to fail gracefully
 			while (true)
 			{
 				int rndCount = read (random, buffer, buffer.Size());
-				throw_sys_sub_if ((rndCount == -1) && errno != EAGAIN, L"/dev/random");
-				if (rndCount == -1 && !DevRandomSucceeded)
+				throw_sys_sub_if ((rndCount == -1) && errno != EAGAIN && errno != ERESTART && errno != EINTR, L"/dev/random");
+				if (rndCount == -1 && (!DevRandomSucceeded || (DevRandomBytesCount < 32)))
 				{
 					// wait 250ms before querying /dev/random again
 					::usleep (250 * 1000);
@@ -57,7 +57,12 @@ namespace VeraCrypt
 				else
 				{
 					if (rndCount != -1)
+					{
+						// We count returned bytes untill 32-bytes treshold reached
+						if (DevRandomBytesCount < 32)
+							DevRandomBytesCount += rndCount;
 						DevRandomSucceeded = true;
+					}
 					break;
 				}
 			}
@@ -236,6 +241,7 @@ namespace VeraCrypt
 		EnrichedByUser = false;
 		Running = false;
 		DevRandomSucceeded = false;
+		DevRandomBytesCount = 0;
 	}
 
 	void RandomNumberGenerator::Test ()
@@ -274,4 +280,5 @@ namespace VeraCrypt
 	size_t RandomNumberGenerator::WriteOffset;
 	struct rand_data *RandomNumberGenerator::JitterRngCtx = NULL;
 	bool RandomNumberGenerator::DevRandomSucceeded = false;
+	int RandomNumberGenerator::DevRandomBytesCount = 0;
 }
diff --git a/src/Core/RandomNumberGenerator.h b/src/Core/RandomNumberGenerator.h
index 9ef45dfe..8f440630 100644
--- a/src/Core/RandomNumberGenerator.h
+++ b/src/Core/RandomNumberGenerator.h
@@ -56,6 +56,7 @@ namespace VeraCrypt
 		static size_t WriteOffset;
 		static struct rand_data *JitterRngCtx;
 		static bool DevRandomSucceeded;
+		static int DevRandomBytesCount;
 	};
 }
 
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