[epiphany/mcatanzaro/getrandom] sync-utils: use getrandom() to generate randomness

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 929f8f4d9e89c7751e6a6f15c1915349a2851c97
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Wed Jan 22 16:11:58 2020 -0600

    sync-utils: use getrandom() to generate randomness
    
    GCC complains that we ignore the return value from fread(), which is
    important for error checking.
    
    This is easy to fix, but might as well switch to getrandom() while we're
    at it, since this is the nice/modern way to get randomness.
    
    Note: requires glibc 2.25 or a newish FreeBSD.

 lib/ephy-sync-utils.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)
---
diff --git a/lib/ephy-sync-utils.c b/lib/ephy-sync-utils.c
index 6c8a37a85..4ae56220b 100644
--- a/lib/ephy-sync-utils.c
+++ b/lib/ephy-sync-utils.c
@@ -23,12 +23,14 @@
 
 #include "ephy-settings.h"
 
+#include <errno.h>
 #include <glib/gi18n.h>
 #include <inttypes.h>
 #include <json-glib/json-glib.h>
 #include <libsoup/soup.h>
 #include <stdio.h>
 #include <string.h>
+#include <sys/random.h>
 
 static const char hex_digits[] = "0123456789abcdef";
 
@@ -165,21 +167,24 @@ ephy_sync_utils_base64_urlsafe_decode (const char *text,
  * This is mainly required by Nettle's RSA support.
  * From Nettle's documentation: random_ctx and random is a randomness generator.
  * random(random_ctx, length, dst) should generate length random octets and store them at dst.
- * We don't really use random_ctx, since we have /dev/urandom available.
+ * We don't use random_ctx.
  */
 void
 ephy_sync_utils_generate_random_bytes (void   *random_ctx,
                                        gsize   num_bytes,
                                        guint8 *out)
 {
-  FILE *fp;
+  gssize ret;
 
   g_assert (num_bytes > 0);
   g_assert (out);
 
-  fp = fopen ("/dev/urandom", "r");
-  fread (out, sizeof (guint8), num_bytes, fp);
-  fclose (fp);
+  do {
+    ret = getrandom (out, num_bytes, 0);
+  } while (ret < (gssize)num_bytes && errno == EINTR);
+
+  if (ret != (gssize)num_bytes)
+    g_error ("Failed to generate randomness: %s", g_strerror (errno));
 }
 
 char *