Drop thread-local fast_rng on fork.

This will cause the child process to construct a new one in a nice
safe way.

Closes ticket 29668; bug not in any released Tor.

diff --git a/src/lib/crypt_ops/crypto_init.c b/src/lib/crypt_ops/crypto_init.c
index cf491f32d1355f01d8794799e485c66ae3b06b0d..5c2780b2ca981652e714bdc2e4a5610ef31eab9e 100644 (file)
--- a/src/lib/crypt_ops/crypto_init.c
+++ b/src/lib/crypt_ops/crypto_init.c
@@ -152,6 +152,12 @@ crypto_prefork(void)
 #ifdef ENABLE_NSS
   crypto_nss_prefork();
 #endif
+  /* It is not safe to share a fast_rng object across a fork boundary unless
+   * we actually have zero-on-fork support in map_anon.c.  If we have
+   * drop-on-fork support, we will crash; if we have neither, we will yield
+   * a copy of the parent process's rng, which is scary and insecure.
+   */
+  destroy_thread_fast_rng();
 }
 
 /** Run operations that the crypto library requires to be happy again