From ecc296ebb74bb17cfb9998972a4bc28b91e82da0 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 26 May 2016 09:26:09 +0100
Subject: [PATCH] rand/noise.c (noise_devrandom): Handle Linux's broken
 `/dev/urandom'.

On Linux, try to open `/dev/random' and make sure it's readable before
proceeding to `/dev/urandom'.  Generally we want to be reading
`/dev/urandom', but not if it hasn't been initialized properly.
---
 rand/noise.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/rand/noise.c b/rand/noise.c
index 5421bc10..6458f92d 100644
--- a/rand/noise.c
+++ b/rand/noise.c
@@ -162,6 +162,21 @@ int noise_devrandom(rand_pool *r)
   ssize_t len;
   size_t n = 0;
   int ret = 0;
+#ifdef __linux__
+  fd_set infd;
+  struct timeval tv = { 0, 0 };
+#endif
+
+#ifdef __linux__
+  /* --- Don't take from `/dev/urandom' if `/dev/random' would block --- */
+
+  if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) < 0) goto done;
+  FD_ZERO(&infd);
+  FD_SET(fd, &infd);
+  if (select(fd + 1, &infd, 0, 0, &tv) < 0 || !FD_ISSET(fd, &infd))
+    goto done;
+  close(fd); fd = -1;
+#endif
 
   /* --- Be nice to other clients of the random device --- *
    *
-- 
2.11.0