Status: New
Owner: ----
New issue 2905 by [email protected]: windows: random number generator has
weak entropy
http://code.google.com/p/v8/issues/detail?id=2905
See https://github.com/joyent/node/issues/6250 for an example.
On Windows, only the current time is used to seed the random number
generator. If you spawn multiple instances of V8 at the same time, they'll
generate the same seed.
I'm not sure if this qualifies as a vulnerability but it's certainly
undesirable behavior.
I've attached a patch that mixes in the PID in order to generate a bit more
entropy. I'm not saying you should take it as-is but maybe it can function
as a starting point.
diff --git a/src/utils/random-number-generator.cc
b/src/utils/random-number-generator.cc
index 1e03ee2..4d286cc 100644
--- a/src/utils/random-number-generator.cc
+++ b/src/utils/random-number-generator.cc
@@ -32,6 +32,7 @@
#include "flags.h"
#include "platform/mutex.h"
#include "platform/time.h"
+#include "platform.h"
#include "utils.h"
namespace v8 {
@@ -85,6 +86,17 @@ RandomNumberGenerator::RandomNumberGenerator() {
int64_t seed = Time::NowFromSystemTime().ToInternalValue() << 24;
seed ^= TimeTicks::HighResNow().ToInternalValue() << 16;
seed ^= TimeTicks::Now().ToInternalValue() << 8;
+ // Mix in the process ID. Run it through a DJB hash to shuffle
+ // the bits around because the PID by itself won't have much
+ // entropy, most of its bits will be zero.
+ uint32_t pid = OS::GetCurrentProcessId();
+ uint64_t hash = 0x1505;
+ hash = (hash * 33) + ((pid >> 0) & 255);
+ hash = (hash * 33) + ((pid >> 8) & 255);
+ hash = (hash * 33) + ((pid >> 16) & 255);
+ hash = (hash * 33) + ((pid >> 24) & 255);
+ hash = ((hash & 0x3FFFFFFFUL) << 32) | (hash & 0xFFFFFFFFUL);
+ seed ^= hash;
SetSeed(seed);
}
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