From fe1e7672efdf22eeb5cbe30d6adc485bc55fa021 Mon Sep 17 00:00:00 2001
From: Milan Crha <mcrha@redhat.com>
Date: Thu, 23 Jul 2026 09:44:31 +0200
Subject: [PATCH] utils: Replace GRand with cryptographically secure random
 generator (CVE-2026-16615)

The GRand is not supposed to be used for cryptography, replace it
with a cryptographically secure random generator and require it
to be available during the setup phase. The library will abort
in case the runtime cannot create a random number (only for
rare cases where the very last fallback to /dev/urandom fails
to read from the device, which is used on some old platforms).

Fixes https://gitlab.gnome.org/GNOME/librest/-/issues/25
---
 meson.build       | 29 ++++++++++++++++++++
 rest/meson.build  |  2 +-
 rest/rest-utils.c | 70 +++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 95 insertions(+), 6 deletions(-)

diff --git a/meson.build b/meson.build
index 4e2a272..2919fb6 100644
--- a/meson.build
+++ b/meson.build
@@ -60,6 +60,8 @@ libsoup_dep = dependency(libsoup_name, version: libsoup_req_version)
 libjson_glib_dep = dependency('json-glib-1.0')
 libxml_dep = dependency('libxml-2.0')
 
+cc = meson.get_compiler('c')
+
 # config.h
 conf = configuration_data()
 conf.set_quoted('PACKAGE_NAME', meson.project_name())
@@ -68,6 +70,33 @@ conf.set_quoted('PACKAGE_VERSION', meson.project_version())
 if get_option('ca_certificates')
   conf.set_quoted('REST_SYSTEM_CA_FILE', ca_certificates_path)
 endif
+
+# CSPRNG detection for secure random string generation (required)
+have_csprng = false
+if cc.has_function('arc4random_buf', prefix: '#include <stdlib.h>')
+  conf.set('HAVE_ARC4RANDOM_BUF', 1)
+  have_csprng = true
+endif
+if cc.has_function('getrandom', prefix: '#include <sys/random.h>')
+  conf.set('HAVE_GETRANDOM', 1)
+  have_csprng = true
+endif
+
+csprng_deps = []
+if host_machine.system() == 'windows'
+  bcrypt_lib = cc.find_library('bcrypt', required: false)
+  if bcrypt_lib.found()
+    csprng_deps += bcrypt_lib
+    conf.set('HAVE_BCRYPTGENRANDOM', 1)
+    have_csprng = true
+  endif
+endif
+
+if not have_csprng
+  error('No cryptographically secure random source found. ' +
+        'librest requires arc4random_buf(), getrandom(), or BCryptGenRandom().')
+endif
+
 config_h = configure_file(output: 'config.h', configuration: conf)
 root_inc = include_directories('.')
 config_dep = declare_dependency(
diff --git a/rest/meson.build b/rest/meson.build
index bfecb9f..1c1cbd5 100644
--- a/rest/meson.build
+++ b/rest/meson.build
@@ -62,7 +62,7 @@ librest_deps = [
   libjson_glib_dep,
   libxml_dep,
   config_dep,
-]
+] + csprng_deps
 
 librest_c_args = [
   '-DG_LOG_DOMAIN="Rest"',
diff --git a/rest/rest-utils.c b/rest/rest-utils.c
index df283e0..346c83b 100644
--- a/rest/rest-utils.c
+++ b/rest/rest-utils.c
@@ -16,29 +16,89 @@
  * Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include "config.h"
 #include "rest-utils.h"
 
+#ifdef HAVE_ARC4RANDOM_BUF
+#include <stdlib.h>
+#endif
+
+#ifdef HAVE_GETRANDOM
+#include <errno.h>
+#include <sys/random.h>
+#endif
+
+#ifdef HAVE_BCRYPTGENRANDOM
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <bcrypt.h>
+#endif
+
+#if defined(HAVE_ARC4RANDOM_BUF)
+
+static void
+crypto_random_bytes (guchar *buffer,
+                     gsize   length)
+{
+  arc4random_buf (buffer, length);
+}
+
+#elif defined(HAVE_BCRYPTGENRANDOM)
+
+static void
+crypto_random_bytes (guchar *buffer,
+                     gsize   length)
+{
+  BCryptGenRandom (NULL, buffer, (ULONG) length,
+                   BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+}
+
+#elif defined(HAVE_GETRANDOM)
+
+static void
+crypto_random_bytes (guchar *buffer,
+                     gsize   length)
+{
+  gsize pos = 0;
+
+  while (pos < length)
+    {
+      gssize ret = getrandom (buffer + pos, length - pos, 0);
+      if (ret < 0)
+        {
+          if (errno == EINTR)
+            continue;
+          g_error ("getrandom() failed: %s", g_strerror (errno));
+        }
+      pos += (gsize) ret;
+    }
+}
+
+#endif /* platform selection */
+
 /**
  * random_string:
  * @length: the length of the random string
  *
- * Creates a random string from a given alphabeth with length @length
+ * Creates a random string from a given alphabet with length @length.
  *
  * Returns: (transfer full): a random string
  */
 gchar *
 random_string (guint length)
 {
-  g_autoptr(GRand) rand = g_rand_new ();
   gchar *buffer = g_malloc0 (sizeof (gchar) * length + 1);
-  gchar alphabeth[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~";
+  gchar alphabet[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~";
+  guint alphabet_len = sizeof (alphabet) - 1;
+  g_autofree guchar *rand_bytes = g_malloc (length);
+
+  crypto_random_bytes (rand_bytes, length);
 
   for (guint i = 0; i < length; i++)
     {
-      buffer[i] = alphabeth[g_rand_int (rand) % (sizeof (alphabeth) - 1)];
+      buffer[i] = alphabet[rand_bytes[i] % alphabet_len];
     }
   buffer[length] = '\0';
 
   return buffer;
 }
-
-- 
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