xref: /third_party/cares/backport-001-CVE-2023-31147.patch

From 823df3b989e59465d17b0a2eb1239a5fc048b4e5 Mon Sep 17 00:00:00 2001
From: Brad House <brad@brad-house.com>
Date: Mon, 22 May 2023 06:51:06 -0400
Subject: [PATCH] Merge pull request from GHSA-8r8p-23f3-64c2

* segment random number generation into own file

* abstract random code to make it more modular so we can have multiple backends

* rand: add support for arc4random_buf() and also direct CARES_RANDOM_FILE reading

* autotools: fix detection of arc4random_buf

* rework initial rc4 seed for PRNG as last fallback

* rc4: more proper implementation, simplified for clarity

* clarifications

Conflict:NA
Reference:https://github.com/c-ares/c-ares/commit/823df3b989e59465d17b0a2eb1239a5fc048b4e5
---
 CMakeLists.txt              |   2 +
 configure.ac                |   1 +
 m4/cares-functions.m4       |  85 +++++++++++
 src/lib/Makefile.inc        |   1 +
 src/lib/ares_config.h.cmake |   3 +
 src/lib/ares_destroy.c      |   3 +
 src/lib/ares_init.c         |  89 ++----------
 src/lib/ares_private.h      |  19 ++-
 src/lib/ares_query.c        |  36 +----
 src/lib/ares_rand.c         | 274 ++++++++++++++++++++++++++++++++++++
 10 files changed, 387 insertions(+), 126 deletions(-)
 create mode 100644 src/lib/ares_rand.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3987d0ab7..e2290af10 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -393,6 +393,8 @@ CHECK_SYMBOL_EXISTS (strncasecmp     "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_STRNCAS
 CHECK_SYMBOL_EXISTS (strncmpi        "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_STRNCMPI)
 CHECK_SYMBOL_EXISTS (strnicmp        "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_STRNICMP)
 CHECK_SYMBOL_EXISTS (writev          "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_WRITEV)
+CHECK_SYMBOL_EXISTS (arc4random_buf  "${CMAKE_EXTRA_INCLUDE_FILES}" HAVE_ARC4RANDOM_BUF)
+
 
 # On Android, the system headers may define __system_property_get(), but excluded
 # from libc.  We need to perform a link test instead of a header/symbol test.
diff --git a/configure.ac b/configure.ac
index 7884cbb26..54e79d6e2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -683,6 +683,7 @@ CARES_CHECK_FUNC_STRNCASECMP
 CARES_CHECK_FUNC_STRNCMPI
 CARES_CHECK_FUNC_STRNICMP
 CARES_CHECK_FUNC_WRITEV
+CARES_CHECK_FUNC_ARC4RANDOM_BUF
 
 
 dnl check for AF_INET6
diff --git a/m4/cares-functions.m4 b/m4/cares-functions.m4
index 0f3992c7f..d4f4f994c 100644
--- a/m4/cares-functions.m4
+++ b/m4/cares-functions.m4
@@ -3753,3 +3753,88 @@ AC_DEFUN([CARES_CHECK_FUNC_WRITEV], [
     ac_cv_func_writev="no"
   fi
 ])
+
+dnl CARES_CHECK_FUNC_ARC4RANDOM_BUF
+dnl -------------------------------------------------
+dnl Verify if arc4random_buf is available, prototyped, and
+dnl can be compiled. If all of these are true, and
+dnl usage has not been previously disallowed with
+dnl shell variable cares_disallow_arc4random_buf, then
+dnl HAVE_ARC4RANDOM_BUF will be defined.
+
+AC_DEFUN([CARES_CHECK_FUNC_ARC4RANDOM_BUF], [
+  AC_REQUIRE([CARES_INCLUDES_STDLIB])dnl
+  #
+  tst_links_arc4random_buf="unknown"
+  tst_proto_arc4random_buf="unknown"
+  tst_compi_arc4random_buf="unknown"
+  tst_allow_arc4random_buf="unknown"
+  #
+  AC_MSG_CHECKING([if arc4random_buf can be linked])
+  AC_LINK_IFELSE([
+    AC_LANG_FUNC_LINK_TRY([arc4random_buf])
+  ],[
+    AC_MSG_RESULT([yes])
+    tst_links_arc4random_buf="yes"
+  ],[
+    AC_MSG_RESULT([no])
+    tst_links_arc4random_buf="no"
+  ])
+  #
+  if test "$tst_links_arc4random_buf" = "yes"; then
+    AC_MSG_CHECKING([if arc4random_buf is prototyped])
+    AC_EGREP_CPP([arc4random_buf],[
+      $cares_includes_stdlib
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_proto_arc4random_buf="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_proto_arc4random_buf="no"
+    ])
+  fi
+  #
+  if test "$tst_proto_arc4random_buf" = "yes"; then
+    AC_MSG_CHECKING([if arc4random_buf is compilable])
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM([[
+        $cares_includes_stdlib
+      ]],[[
+          arc4random_buf(NULL, 0);
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_arc4random_buf="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_arc4random_buf="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_arc4random_buf" = "yes"; then
+    AC_MSG_CHECKING([if arc4random_buf usage allowed])
+    if test "x$cares_disallow_arc4random_buf" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_arc4random_buf="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_arc4random_buf="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if arc4random_buf might be used])
+  if test "$tst_links_arc4random_buf" = "yes" &&
+     test "$tst_proto_arc4random_buf" = "yes" &&
+     test "$tst_compi_arc4random_buf" = "yes" &&
+     test "$tst_allow_arc4random_buf" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_ARC4RANDOM_BUF, 1,
+      [Define to 1 if you have the arc4random_buf function.])
+    ac_cv_func_arc4random_buf="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_arc4random_buf="no"
+  fi
+])
+
diff --git a/src/lib/Makefile.inc b/src/lib/Makefile.inc
index 140378d67..49bbe6016 100644
--- a/src/lib/Makefile.inc
+++ b/src/lib/Makefile.inc
@@ -45,6 +45,7 @@ CSOURCES = ares__addrinfo2hostent.c	\
   ares_platform.c			\
   ares_process.c			\
   ares_query.c				\
+  ares_rand.c \
   ares_search.c				\
   ares_send.c				\
   ares_strcasecmp.c			\
diff --git a/src/lib/ares_config.h.cmake b/src/lib/ares_config.h.cmake
index fddb78535..798820a3a 100644
--- a/src/lib/ares_config.h.cmake
+++ b/src/lib/ares_config.h.cmake
@@ -346,6 +346,9 @@
 /* Define to 1 if you need the memory.h header file even with stdlib.h */
 #cmakedefine NEED_MEMORY_H
 
+/* Define if have arc4random_buf() */
+#cmakedefine HAVE_ARC4RANDOM_BUF
+
 /* a suitable file/device to read random data from */
 #cmakedefine CARES_RANDOM_FILE "@CARES_RANDOM_FILE@"
 
diff --git a/src/lib/ares_destroy.c b/src/lib/ares_destroy.c
index 7ec2bde5a..62c899f82 100644
--- a/src/lib/ares_destroy.c
+++ b/src/lib/ares_destroy.c
@@ -95,6 +95,9 @@ void ares_destroy(ares_channel channel)
   if (channel->resolvconf_path)
     ares_free(channel->resolvconf_path);
 
+  if (channel->rand_state)
+    ares__destroy_rand_state(channel->rand_state);
+
   ares_free(channel);
 }
 
diff --git a/src/lib/ares_init.c b/src/lib/ares_init.c
index c7ca7af1b..0519f43e5 100644
--- a/src/lib/ares_init.c
+++ b/src/lib/ares_init.c
@@ -87,7 +76,6 @@ static int config_nameserver(struct server_state **servers, int *nservers,
 static int set_search(ares_channel channel, const char *str);
 static int set_options(ares_channel channel, const char *str);
 static const char *try_option(const char *p, const char *q, const char *opt);
-static int init_id_key(rc4_key* key,int key_data_len);
 
 static int config_sortlist(struct apattern **sortlist, int *nsort,
                            const char *str);
@@ -165,6 +153,7 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   channel->sock_funcs = NULL;
   channel->sock_func_cb_data = NULL;
   channel->resolvconf_path = NULL;
+  channel->rand_state = NULL;
 
   channel->last_server = 0;
   channel->last_timeout_processed = (time_t)now.tv_sec;
@@ -218,9 +207,13 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   /* Generate random key */
 
   if (status == ARES_SUCCESS) {
-    status = init_id_key(&channel->id_key, ARES_ID_KEY_LEN);
+    channel->rand_state = ares__init_rand_state();
+    if (channel->rand_state == NULL) {
+      status = ARES_ENOMEM;
+    }
+
     if (status == ARES_SUCCESS)
-      channel->next_id = ares__generate_new_id(&channel->id_key);
+      channel->next_id = ares__generate_new_id(channel->rand_state);
     else
       DEBUGF(fprintf(stderr, "Error: init_id_key failed: %s\n",
                      ares_strerror(status)));
@@ -242,6 +235,8 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
         ares_free(channel->lookups);
       if(channel->resolvconf_path)
         ares_free(channel->resolvconf_path);
+      if (channel->rand_state)
+        ares__destroy_rand_state(channel->rand_state);
       ares_free(channel);
       return status;
     }
@@ -2182,76 +2177,6 @@ static int sortlist_alloc(struct apattern **sortlist, int *nsort,
   return 1;
 }
 
-/* initialize an rc4 key. If possible a cryptographically secure random key
-   is generated using a suitable function (for example win32's RtlGenRandom as
-   described in
-   http://blogs.msdn.com/michael_howard/archive/2005/01/14/353379.aspx
-   otherwise the code defaults to cross-platform albeit less secure mechanism
-   using rand
-*/
-static void randomize_key(unsigned char* key,int key_data_len)
-{
-  int randomized = 0;
-  int counter=0;
-#ifdef WIN32
-  BOOLEAN res;
-  if (ares_fpSystemFunction036)
-    {
-      res = (*ares_fpSystemFunction036) (key, key_data_len);
-      if (res)
-        randomized = 1;
-    }
-#else /* !WIN32 */
-#ifdef CARES_RANDOM_FILE
-  FILE *f = fopen(CARES_RANDOM_FILE, "rb");
-  if(f) {
-    setvbuf(f, NULL, _IONBF, 0);
-    counter = aresx_uztosi(fread(key, 1, key_data_len, f));
-    fclose(f);
-  }
-#endif
-#endif /* WIN32 */
-
-  if (!randomized) {
-    for (;counter<key_data_len;counter++)
-      key[counter]=(unsigned char)(rand() % 256);  /* LCOV_EXCL_LINE */
-  }
-}
-
-static int init_id_key(rc4_key* key,int key_data_len)
-{
-  unsigned char index1;
-  unsigned char index2;
-  unsigned char* state;
-  short counter;
-  unsigned char *key_data_ptr = 0;
-
-  key_data_ptr = ares_malloc(key_data_len);
-  if (!key_data_ptr)
-    return ARES_ENOMEM;
-  memset(key_data_ptr, 0, key_data_len);
-
-  state = &key->state[0];
-  for(counter = 0; counter < 256; counter++)
-    /* unnecessary AND but it keeps some compilers happier */
-    state[counter] = (unsigned char)(counter & 0xff);
-  randomize_key(key->state,key_data_len);
-  key->x = 0;
-  key->y = 0;
-  index1 = 0;
-  index2 = 0;
-  for(counter = 0; counter < 256; counter++)
-  {
-    index2 = (unsigned char)((key_data_ptr[index1] + state[counter] +
-                              index2) % 256);
-    ARES_SWAP_BYTE(&state[counter], &state[index2]);
-
-    index1 = (unsigned char)((index1 + 1) % key_data_len);
-  }
-  ares_free(key_data_ptr);
-  return ARES_SUCCESS;
-}
-
 void ares_set_local_ip4(ares_channel channel, unsigned int local_ip)
 {
   channel->local_ip4 = local_ip;
diff --git a/src/lib/ares_private.h b/src/lib/ares_private.h
index 53043a651..b6eab8a7d 100644
--- a/src/lib/ares_private.h
+++ b/src/lib/ares_private.h
@@ -101,8 +101,6 @@ W32_FUNC const char *_w32_GetHostsFile (void);
 
 #endif
 
-#define ARES_ID_KEY_LEN 31
-
 #include "ares_ipv6.h"
 #include "ares_llist.h"
 
@@ -262,12 +260,8 @@ struct apattern {
   unsigned short type;
 };
 
-typedef struct rc4_key
-{
-  unsigned char state[256];
-  unsigned char x;
-  unsigned char y;
-} rc4_key;
+struct ares_rand_state;
+typedef struct ares_rand_state ares_rand_state;
 
 struct ares_channeldata {
   /* Configuration data */
@@ -302,8 +296,8 @@ struct ares_channeldata {
 
   /* ID to use for next query */
   unsigned short next_id;
-  /* key to use when generating new ids */
-  rc4_key id_key;
+  /* random state to use when generating new ids */
+  ares_rand_state *rand_state;
 
   /* Generation number to use for the next TCP socket open/close */
   int tcp_connection_generation;
@@ -362,7 +356,10 @@ void ares__close_sockets(ares_channel channel, struct server_state *server);
 int ares__get_hostent(FILE *fp, int family, struct hostent **host);
 int ares__read_line(FILE *fp, char **buf, size_t *bufsize);
 void ares__free_query(struct query *query);
-unsigned short ares__generate_new_id(rc4_key* key);
+
+ares_rand_state *ares__init_rand_state(void);
+void ares__destroy_rand_state(ares_rand_state *state);
+unsigned short ares__generate_new_id(ares_rand_state *state);
 struct timeval ares__tvnow(void);
 int ares__expand_name_validated(const unsigned char *encoded,
                                 const unsigned char *abuf,
diff --git a/src/lib/ares_query.c b/src/lib/ares_query.c
index 508274db3..42323bec5 100644
--- a/src/lib/ares_query.c
+++ b/src/lib/ares_query.c
@@ -33,32 +33,6 @@ struct qquery {
 
 static void qcallback(void *arg, int status, int timeouts, unsigned char *abuf, int alen);
 
-static void rc4(rc4_key* key, unsigned char *buffer_ptr, int buffer_len)
-{
-  unsigned char x;
-  unsigned char y;
-  unsigned char* state;
-  unsigned char xorIndex;
-  int counter;
-
-  x = key->x;
-  y = key->y;
-
-  state = &key->state[0];
-  for(counter = 0; counter < buffer_len; counter ++)
-  {
-    x = (unsigned char)((x + 1) % 256);
-    y = (unsigned char)((state[x] + y) % 256);
-    ARES_SWAP_BYTE(&state[x], &state[y]);
-
-    xorIndex = (unsigned char)((state[x] + state[y]) % 256);
-
-    buffer_ptr[counter] = (unsigned char)(buffer_ptr[counter]^state[xorIndex]);
-  }
-  key->x = x;
-  key->y = y;
-}
-
 static struct query* find_query_by_id(ares_channel channel, unsigned short id)
 {
   unsigned short qid;
@@ -78,7 +52,6 @@ static struct query* find_query_by_id(ares_channel channel, unsigned short id)
   return NULL;
 }
 
-
 /* a unique query id is generated using an rc4 key. Since the id may already
    be used by a running query (as infrequent as it may be), a lookup is
    performed per id generation. In practice this search should happen only
@@ -89,19 +62,12 @@ static unsigned short generate_unique_id(ares_channel channel)
   unsigned short id;
 
   do {
-    id = ares__generate_new_id(&channel->id_key);
+    id = ares__generate_new_id(channel->rand_state);
   } while (find_query_by_id(channel, id));
 
   return (unsigned short)id;
 }
 
-unsigned short ares__generate_new_id(rc4_key* key)
-{
-  unsigned short r=0;
-  rc4(key, (unsigned char *)&r, sizeof(r));
-  return r;
-}
-
 void ares_query(ares_channel channel, const char *name, int dnsclass,
                 int type, ares_callback callback, void *arg)
 {
diff --git a/src/lib/ares_rand.c b/src/lib/ares_rand.c
new file mode 100644
index 000000000..a564bc236
--- /dev/null
+++ b/src/lib/ares_rand.c
@@ -0,0 +1,274 @@
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ * Copyright (C) 2007-2013 by Daniel Stenberg
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "ares_setup.h"
+#include "ares.h"
+#include "ares_private.h"
+#include "ares_nowarn.h"
+#include <stdlib.h>
+
+typedef enum  {
+  ARES_RAND_OS   = 1,  /* OS-provided such as RtlGenRandom or arc4random */
+  ARES_RAND_FILE = 2,  /* OS file-backed random number generator */
+  ARES_RAND_RC4  = 3   /* Internal RC4 based PRNG */
+} ares_rand_backend;
+
+typedef struct ares_rand_rc4
+{
+  unsigned char S[256];
+  size_t        i;
+  size_t        j;
+} ares_rand_rc4;
+
+struct ares_rand_state
+{
+  ares_rand_backend type;
+  union {
+    FILE *rand_file;
+    ares_rand_rc4 rc4;
+  } state;
+};
+
+
+/* Define RtlGenRandom = SystemFunction036.  This is in advapi32.dll.  There is
+ * no need to dynamically load this, other software used widely does not.
+ * http://blogs.msdn.com/michael_howard/archive/2005/01/14/353379.aspx
+ * https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
+ */
+#ifdef _WIN32
+BOOLEAN WINAPI SystemFunction036(PVOID RandomBuffer, ULONG RandomBufferLength);
+#  ifndef RtlGenRandom
+#    define RtlGenRandom(a,b) SystemFunction036(a,b)
+#  endif
+#endif
+
+
+#define ARES_RC4_KEY_LEN 32 /* 256 bits */
+
+static unsigned int ares_u32_from_ptr(void *addr)
+{
+    if (sizeof(void *) == 8) {
+        return (unsigned int)((((size_t)addr >> 32) & 0xFFFFFFFF) | ((size_t)addr & 0xFFFFFFFF));
+    }
+    return (unsigned int)((size_t)addr & 0xFFFFFFFF);
+}
+
+
+/* initialize an rc4 key as the last possible fallback. */
+static void ares_rc4_generate_key(ares_rand_rc4 *rc4_state, unsigned char *key, size_t key_len)
+{
+  size_t         i;
+  size_t         len = 0;
+  unsigned int   data;
+  struct timeval tv;
+
+  if (key_len != ARES_RC4_KEY_LEN)
+    return;
+
+  /* Randomness is hard to come by.  Maybe the system randomizes heap and stack addresses.
+   * Maybe the current timestamp give us some randomness.
+   * Use  rc4_state (heap), &i (stack), and ares__tvnow()
+   */
+  data = ares_u32_from_ptr(rc4_state);
+  memcpy(key + len, &data, sizeof(data));
+  len += sizeof(data);
+
+  data = ares_u32_from_ptr(&i);
+  memcpy(key + len, &data, sizeof(data));
+  len += sizeof(data);
+
+  tv = ares__tvnow();
+  data = (unsigned int)((tv.tv_sec | tv.tv_usec) & 0xFFFFFFFF);
+  memcpy(key + len, &data, sizeof(data));
+  len += sizeof(data);
+
+  srand(ares_u32_from_ptr(rc4_state) | ares_u32_from_ptr(&i) | (unsigned int)((tv.tv_sec | tv.tv_usec) & 0xFFFFFFFF));
+
+  for (i=len; i<key_len; i++) {
+    key[i]=(unsigned char)(rand() % 256);  /* LCOV_EXCL_LINE */
+  }
+}
+
+
+static void ares_rc4_init(ares_rand_rc4 *rc4_state)
+{
+  unsigned char key[ARES_RC4_KEY_LEN];
+  size_t        i;
+  size_t        j;
+
+  ares_rc4_generate_key(rc4_state, key, sizeof(key));
+
+  for (i = 0; i < sizeof(rc4_state->S); i++) {
+    rc4_state->S[i] = i & 0xFF;
+  }
+
+  for(i = 0, j = 0; i < 256; i++) {
+    j = (j + rc4_state->S[i] + key[i % sizeof(key)]) % 256;
+    ARES_SWAP_BYTE(&rc4_state->S[i], &rc4_state->S[j]);
+  }
+
+  rc4_state->i = 0;
+  rc4_state->j = 0;
+}
+
+/* Just outputs the key schedule, no need to XOR with any data since we have none */
+static void ares_rc4_prng(ares_rand_rc4 *rc4_state, unsigned char *buf, int len)
+{
+  unsigned char *S = rc4_state->S;
+  size_t         i = rc4_state->i;
+  size_t         j = rc4_state->j;
+  size_t         cnt;
+
+  for (cnt=0; cnt<len; cnt++) {
+    i = (i + 1) % 256;
+    j = (j + S[i]) % 256;
+
+    ARES_SWAP_BYTE(&S[i], &S[j]);
+    buf[cnt] = S[(S[i] + S[j]) % 256];
+  }
+
+  rc4_state->i = i;
+  rc4_state->j = j;
+}
+
+
+static int ares__init_rand_engine(ares_rand_state *state)
+{
+  memset(state, 0, sizeof(*state));
+
+#if defined(HAVE_ARC4RANDOM_BUF) || defined(_WIN32)
+  state->type = ARES_RAND_OS;
+  return 1;
+#elif defined(CARES_RANDOM_FILE)
+  state->type            = ARES_RAND_FILE;
+  state->state.rand_file = fopen(CARES_RANDOM_FILE, "rb");
+  if (state->state.rand_file) {
+    setvbuf(state->state.rand_file, NULL, _IONBF, 0);
+    return 1;
+  }
+  /* Fall-Thru on failure to RC4 */
+#endif
+
+  state->type = ARES_RAND_RC4;
+  ares_rc4_init(&state->state.rc4);
+
+  /* Currently cannot fail */
+  return 1;
+}
+
+
+ares_rand_state *ares__init_rand_state()
+{
+  ares_rand_state *state = NULL;
+
+  state = ares_malloc(sizeof(*state));
+  if (!state)
+    return NULL;
+
+  if (!ares__init_rand_engine(state)) {
+    ares_free(state);
+    return NULL;
+  }
+
+  return state;
+}
+
+
+static void ares__clear_rand_state(ares_rand_state *state)
+{
+  if (!state)
+    return;
+
+  switch (state->type) {
+    case ARES_RAND_OS:
+      break;
+    case ARES_RAND_FILE:
+      fclose(state->state.rand_file);
+      break;
+    case ARES_RAND_RC4:
+      break;
+  }
+}
+
+
+static void ares__reinit_rand(ares_rand_state *state)
+{
+  ares__clear_rand_state(state);
+  ares__init_rand_engine(state);
+}
+
+
+void ares__destroy_rand_state(ares_rand_state *state)
+{
+  if (!state)
+    return;
+
+  ares__clear_rand_state(state);
+  ares_free(state);
+}
+
+
+static void ares__rand_bytes(ares_rand_state *state, unsigned char *buf, size_t len)
+{
+
+  while (1) {
+    size_t rv;
+    size_t bytes_read = 0;
+
+    switch (state->type) {
+      case ARES_RAND_OS:
+#ifdef _WIN32
+        RtlGenRandom(buf, len);
+        return;
+#elif defined(HAVE_ARC4RANDOM_BUF)
+        arc4random_buf(buf, len);
+        return;
+#else
+        /* Shouldn't be possible to be here */
+        break;
+#endif
+
+      case ARES_RAND_FILE:
+        while (1) {
+          size_t rv = fread(buf + bytes_read, 1, len - bytes_read, state->state.rand_file);
+          if (rv == 0)
+            break; /* critical error, will reinit rand state */
+
+          bytes_read += rv;
+          if (bytes_read == len)
+            return;
+        }
+        break;
+
+      case ARES_RAND_RC4:
+        ares_rc4_prng(&state->state.rc4, buf, len);
+        return;
+    }
+
+    /* If we didn't return before we got here, that means we had a critical rand
+     * failure and need to reinitialized */
+    ares__reinit_rand(state);
+  }
+}
+
+unsigned short ares__generate_new_id(ares_rand_state *state)
+{
+  unsigned short r=0;
+
+  ares__rand_bytes(state, (unsigned char *)&r, sizeof(r));
+  return r;
+}
+