From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 26 May 2016 08:26:09 +0000 (+0100)
Subject: rand/noise.c (noise_devrandom): Handle Linux's broken `/dev/urandom'.
X-Git-Tag: 2.2.3~1^2~7
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/catacomb/commitdiff_plain/ecc296ebb74bb17cfb9998972a4bc28b91e82da0

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.
---

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 --- *
    *