sysdep: Add wrapper to get random bytes

Add a wrapper function in sysdep to get random bytes, and required checks
in configure.ac to select how to do it. The configure script tries, in
order, getrandom(), getentropy() and reading from /dev/urandom.

2 files changed, 89 insertions, 0 deletions

diff --git a/sysdep/unix/main.c b/sysdep/unix/main.c
index 76f92c5e..392aff9d 100644
--- a/sysdep/unix/main.c
+++ b/sysdep/unix/main.c
@@ -867,6 +867,7 @@ main(int argc, char **argv)
   parse_args(argc, argv);
   log_switch(1, NULL, NULL);
 
+  random_init();
   net_init();
   resource_init();
   timer_init();
diff --git a/sysdep/unix/random.c b/sysdep/unix/random.c
index b1f5086f..de81f3ca 100644
--- a/sysdep/unix/random.c
+++ b/sysdep/unix/random.c
@@ -7,6 +7,21 @@
  */
 
 #include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "sysdep/config.h"
+
+#ifdef HAVE_SYS_STAT_H
+#  include <sys/stat.h>
+#endif
+#ifdef HAVE_LINUX_RANDOM_H
+#  include <linux/random.h>
+#endif
+#if defined(HAVE_SYS_RANDOM_H) && (defined(HAVE_GETRANDOM) || defined(HAVE_GETENTROPY))
+#    include <sys/random.h>
+#endif
 
 #include "nest/bird.h"
 
@@ -19,3 +34,76 @@ random_u32(void)
   rand_high = random();
   return (rand_low & 0xffff) | ((rand_high & 0xffff) << 16);
 }
+
+void
+random_init()
+{
+  char buf;
+  /* get a single random byte to trip any errors early */
+  random_bytes(&buf, sizeof(buf));
+}
+
+#if defined(HAVE_GETRANDOM) || defined(HAVE_GENTROPY)
+int
+random_bytes(char *buf, size_t size)
+{
+  int n;
+  int flags = 0;
+  while (0 < size) {
+#if defined(HAVE_GETRANDOM)
+    n = getrandom(buf, size, flags);
+#else
+    n = getentropy(buf, size);
+#endif
+    if (n < 0) {
+      if (errno == EINTR)
+        continue;
+      die("Couldn't get random bytes: %m");
+    }
+    buf += n;
+    size -= n;
+  }
+
+  return 0;
+}
+
+void random_close(void) {}
+
+#else
+
+static int urandom_fd = -1;
+int random_bytes(char *buf, size_t size)
+{
+  int n;
+
+  if (urandom_fd < 0)
+  {
+    urandom_fd = open("/dev/urandom", O_RDONLY);
+    if (urandom_fd < 0)
+      die("Couldn't open /dev/urandom: %m");
+  }
+
+  do
+  {
+    n = read(urandom_fd, buf, size);
+    if (n <= 0) {
+      if (errno == EINTR)
+        continue;
+      die("Couldn't read from /dev/urandom: %m");
+    }
+    buf += n;
+    size -= n;
+  } while (size > 0);
+
+  return 0;
+}
+
+void
+random_close(void)
+{
+  if (urandom_fd >= 0) {
+    close(urandom_fd);
+    urandom_fd = -1;
+  }
+}
+#endif