Resolve #647

Implement a backoff approach to opening the system RNG: if opening read-write fails, try to open read-only. This will allow the RNG to be used, but attempts to add entropy will fail. If opening as read-only also fails, only then throw an exception.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/lib/rng/system_rng/system_rng.cpp b/src/lib/rng/system_rng/system_rng.cpp
index 135f4fabd..1ea749327 100644
--- a/src/lib/rng/system_rng/system_rng.cpp
+++ b/src/lib/rng/system_rng/system_rng.cpp
@@ -75,6 +75,12 @@ System_RNG_Impl::System_RNG_Impl()
 #endif
 
    m_fd = ::open(BOTAN_SYSTEM_RNG_DEVICE, O_RDWR | O_NOCTTY);
+   
+   // Cannot open in read-write mode. Fall back to read-only
+   // Calls to add_entropy will fail, but randomize will work
+   if(m_fd < 0)
+      m_fd = ::open(BOTAN_SYSTEM_RNG_DEVICE, O_RDONLY | O_NOCTTY);
+
    if(m_fd < 0)
       throw Exception("System_RNG failed to open RNG device");
 #endif