Fix numerous problems with Tor's weak RNG.

We need a weak RNG in a couple of places where the strong RNG is
both needless and too slow.  We had been using the weak RNG from our
platform's libc implementation, but that was problematic (because
many platforms have exceptionally horrible weak RNGs -- like, ones
that only return values between 0 and SHORT_MAX) and because we were
using it in a way that was wrong for LCG-based weak RNGs.  (We were
counting on the low bits of the LCG output to be as random as the
high ones, which isn't true.)

This patch adds a separate type for a weak RNG, adds an LCG
implementation for it, and uses that exclusively where we had been
using the platform weak RNG.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/common/crypto.c b/src/common/crypto.c
index 70bd45299..22d57c7c8 100644
--- a/src/common/crypto.c
+++ b/src/common/crypto.c
@@ -2337,12 +2337,12 @@ crypto_dh_free(crypto_dh_t *dh)
   (OPENSSL_VERSION_NUMBER >= OPENSSL_V(0,9,8,'c'))
 
 /** Set the seed of the weak RNG to a random value. */
-static void
-seed_weak_rng(void)
+void
+crypto_seed_weak_rng(tor_weak_rng_t *rng)
 {
   unsigned seed;
   crypto_rand((void*)&seed, sizeof(seed));
-  tor_init_weak_random(seed);
+  tor_init_weak_random(rng, seed);
 }
 
 /** Try to get <b>out_len</b> bytes of the strongest entropy we can generate,
@@ -2426,7 +2426,7 @@ crypto_seed_rng(int startup)
   }
 
   memwipe(buf, 0, sizeof(buf));
-  seed_weak_rng();
+
   if (rand_poll_ok || load_entropy_ok)
     return 0;
   else