formpost: better random boundaries

When doing multi-part formposts, libcurl used a pseudo-random value that
was seeded with time(). This turns out to be bad for users who formpost
data that is provided with users who then can guess how the boundary
string will look like and then they can forge a different formpost part
and trick the receiver.

My advice to such implementors is (still even after this change) to not
rely on the boundary strings being cryptographically strong. Fix your
code and logic to not depend on them that much!

I moved the Curl_rand() function into the sslgen.c source file now to be
able to take advantage of the SSL library's random function if it
provides one. If not, try to use the RANDOM_FILE for seeding and as a
last resort keep the old logic, just modified to also add microseconds
which makes it harder to properly guess the exact seed.

The formboundary() function in formdata.c is now using 64 bit entropy
for the boundary and therefore the string of dashes was reduced by 4
letters and there are 16 hex digits following it. The total length is
thus still the same.

Bug: http://curl.haxx.se/bug/view.cgi?id=1251
Reported-by: "Floris"

12 files changed, 115 insertions, 135 deletions

diff --git a/lib/Makefile.inc b/lib/Makefile.inc
index 4228bf6b8..f3845a0fb 100644
--- a/lib/Makefile.inc
+++ b/lib/Makefile.inc
@@ -13,7 +13,7 @@ CSOURCES = file.c timeval.c base64.c hostip.c progress.c formdata.c	\
   netrc.c getinfo.c transfer.c strequal.c easy.c security.c krb4.c	\
   curl_fnmatch.c fileinfo.c ftplistparser.c wildcard.c krb5.c		\
   memdebug.c http_chunks.c strtok.c connect.c llist.c hash.c multi.c	\
-  content_encoding.c share.c http_digest.c md4.c md5.c curl_rand.c	\
+  content_encoding.c share.c http_digest.c md4.c md5.c	\
   http_negotiate.c inet_pton.c strtoofft.c strerror.c amigaos.c		\
   hostasyn.c hostip4.c hostip6.c hostsyn.c inet_ntop.c parsedate.c	\
   select.c gtls.c sslgen.c tftp.c splay.c strdup.c socks.c ssh.c nss.c	\
@@ -30,7 +30,7 @@ CSOURCES = file.c timeval.c base64.c hostip.c progress.c formdata.c	\
 HHEADERS = arpa_telnet.h netrc.h file.h timeval.h qssl.h hostip.h	\
   progress.h formdata.h cookie.h http.h sendf.h ftp.h url.h dict.h	\
   if2ip.h speedcheck.h urldata.h curl_ldap.h ssluse.h escape.h telnet.h	\
-  getinfo.h strequal.h krb4.h memdebug.h http_chunks.h curl_rand.h	\
+  getinfo.h strequal.h krb4.h memdebug.h http_chunks.h	\
   curl_fnmatch.h wildcard.h fileinfo.h ftplistparser.h strtok.h		\
   connect.h llist.h hash.h content_encoding.h share.h curl_md4.h	\
   curl_md5.h http_digest.h http_negotiate.h inet_pton.h amigaos.h	\
diff --git a/lib/curl_darwinssl.h b/lib/curl_darwinssl.h
index 4c0e53ff1..432d3d7ce 100644
--- a/lib/curl_darwinssl.h
+++ b/lib/curl_darwinssl.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 2012, Nick Zitzmann, <nickzman@gmail.com>.
+ * Copyright (C) 2012 - 2013, Nick Zitzmann, <nickzman@gmail.com>.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -52,6 +52,10 @@ void Curl_darwinssl_md5sum(unsigned char *tmp, /* input */
                            unsigned char *md5sum, /* output */
                            size_t md5len);
 
+/* this backend provides these functions: */
+#define have_curlssl_random 1
+#define have_curlssl_md5sum 1
+
 /* API setup for SecureTransport */
 #define curlssl_init() (1)
 #define curlssl_cleanup() Curl_nop_stmt
diff --git a/lib/curl_rand.c b/lib/curl_rand.c
deleted file mode 100644
index dc49289a1..000000000
--- a/lib/curl_rand.c
+++ /dev/null
@@ -1,61 +0,0 @@
-/***************************************************************************
- *                                  _   _ ____  _
- *  Project                     ___| | | |  _ \| |
- *                             / __| | | | |_) | |
- *                            | (__| |_| |  _ <| |___
- *                             \___|\___/|_| \_\_____|
- *
- * Copyright (C) 1998 - 2009, Daniel Stenberg, <daniel@haxx.se>, et al.
- *
- * This software is licensed as described in the file COPYING, which
- * you should have received as part of this distribution. The terms
- * are also available at http://curl.haxx.se/docs/copyright.html.
- *
- * You may opt to use, copy, modify, merge, publish, distribute and/or sell
- * copies of the Software, and permit persons to whom the Software is
- * furnished to do so, under the terms of the COPYING file.
- *
- * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
- * KIND, either express or implied.
- *
- ***************************************************************************/
-
-#include "curl_setup.h"
-
-#include <curl/curl.h>
-
-#include "curl_rand.h"
-
-#define _MPRINTF_REPLACE /* use our functions only */
-#include <curl/mprintf.h>
-
-#include "curl_memory.h"
-/* The last #include file should be: */
-#include "memdebug.h"
-
-/* Private pseudo-random number seed. Unsigned integer >= 32bit. Threads
-   mutual exclusion is not implemented to acess it since we do not require
-   high quality random numbers (only used in form boudary generation). */
-
-static unsigned int randseed;
-
-/* Pseudo-random number support. */
-
-unsigned int Curl_rand(void)
-{
-  unsigned int r;
-  /* Return an unsigned 32-bit pseudo-random number. */
-  r = randseed = randseed * 1103515245 + 12345;
-  return (r << 16) | ((r >> 16) & 0xFFFF);
-}
-
-void Curl_srand(void)
-{
-  /* Randomize pseudo-random number sequence. */
-
-  randseed = (unsigned int) time(NULL);
-  Curl_rand();
-  Curl_rand();
-  Curl_rand();
-}
-
diff --git a/lib/curl_rand.h b/lib/curl_rand.h
deleted file mode 100644
index 26cfb7f03..000000000
--- a/lib/curl_rand.h
+++ /dev/null
@@ -1,29 +0,0 @@
-#ifndef HEADER_CURL_RAND_H
-#define HEADER_CURL_RAND_H
-/***************************************************************************
- *                                  _   _ ____  _
- *  Project                     ___| | | |  _ \| |
- *                             / __| | | | |_) | |
- *                            | (__| |_| |  _ <| |___
- *                             \___|\___/|_| \_\_____|
- *
- * Copyright (C) 1998 - 2009, Daniel Stenberg, <daniel@haxx.se>, et al.
- *
- * This software is licensed as described in the file COPYING, which
- * you should have received as part of this distribution. The terms
- * are also available at http://curl.haxx.se/docs/copyright.html.
- *
- * You may opt to use, copy, modify, merge, publish, distribute and/or sell
- * copies of the Software, and permit persons to whom the Software is
- * furnished to do so, under the terms of the COPYING file.
- *
- * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
- * KIND, either express or implied.
- *
- ***************************************************************************/
-
-void Curl_srand(void);
-
-unsigned int Curl_rand(void);
-
-#endif /* HEADER_CURL_RAND_H */
diff --git a/lib/curl_sasl.c b/lib/curl_sasl.c
index 39d451a37..fcb001948 100644
--- a/lib/curl_sasl.c
+++ b/lib/curl_sasl.c
@@ -32,7 +32,7 @@
 
 #include "curl_base64.h"
 #include "curl_md5.h"
-#include "curl_rand.h"
+#include "sslgen.h"
 #include "curl_hmac.h"
 #include "curl_ntlm_msgs.h"
 #include "curl_sasl.h"
@@ -314,7 +314,7 @@ CURLcode Curl_sasl_create_digest_md5_message(struct SessionHandle *data,
 
   /* Generate 64 bits of random data */
   for(i = 0; i < 8; i++)
-    cnonce[i] = table16[Curl_rand()%16];
+    cnonce[i] = table16[Curl_rand(data)%16];
 
   /* So far so good, now calculate A1 and H(A1) according to RFC 2831 */
   ctxt = Curl_MD5_init(Curl_DIGEST_MD5);
diff --git a/lib/easy.c b/lib/easy.c
index 51da1c254..9d4e01176 100644
--- a/lib/easy.c
+++ b/lib/easy.c
@@ -74,7 +74,6 @@
 #include "connect.h" /* for Curl_getconnectinfo */
 #include "slist.h"
 #include "amigaos.h"
-#include "curl_rand.h"
 #include "non-ascii.h"
 #include "warnless.h"
 #include "conncache.h"
@@ -330,10 +329,6 @@ CURLcode curl_global_init(long flags)
 
   init_flags  = flags;
 
-  /* Preset pseudo-random number sequence. */
-
-  Curl_srand();
-
   return CURLE_OK;
 }
 
diff --git a/lib/formdata.c b/lib/formdata.c
index 49c5d2943..decb84d9f 100644
--- a/lib/formdata.c
+++ b/lib/formdata.c
@@ -24,9 +24,6 @@
 
 #include <curl/curl.h>
 
-/* Length of the random boundary string. */
-#define BOUNDARY_LENGTH 40
-
 #if !defined(CURL_DISABLE_HTTP) || defined(USE_SSLEAY)
 
 #if defined(HAVE_LIBGEN_H) && defined(HAVE_BASENAME)
@@ -35,7 +32,7 @@
 
 #include "urldata.h" /* for struct SessionHandle */
 #include "formdata.h"
-#include "curl_rand.h"
+#include "sslgen.h"
 #include "strequal.h"
 #include "curl_memory.h"
 #include "sendf.h"
@@ -56,7 +53,7 @@ static char *Curl_basename(char *path);
 #endif
 
 static size_t readfromfile(struct Form *form, char *buffer, size_t size);
-static char *formboundary(void);
+static char *formboundary(struct SessionHandle *data);
 
 /* What kind of Content-Type to use on un-specified files with unrecognized
    extensions. */
@@ -1101,7 +1098,7 @@ CURLcode Curl_getformdata(struct SessionHandle *data,
   if(!post)
     return result; /* no input => no output! */
 
-  boundary = formboundary();
+  boundary = formboundary(data);
   if(!boundary)
     return CURLE_OUT_OF_MEMORY;
 
@@ -1157,7 +1154,7 @@ CURLcode Curl_getformdata(struct SessionHandle *data,
          the magic to include several files with the same field name */
 
       Curl_safefree(fileboundary);
-      fileboundary = formboundary();
+      fileboundary = formboundary(data);
       if(!fileboundary) {
         result = CURLE_OUT_OF_MEMORY;
         break;
@@ -1464,28 +1461,12 @@ char *Curl_formpostheader(void *formp, size_t *len)
  * formboundary() creates a suitable boundary string and returns an allocated
  * one.
  */
-static char *formboundary(void)
+static char *formboundary(struct SessionHandle *data)
 {
-  char *retstring;
-  size_t i;
-
-  static const char table16[]="0123456789abcdef";
-
-  retstring = malloc(BOUNDARY_LENGTH+1);
-
-  if(!retstring)
-    return NULL; /* failed */
-
-  strcpy(retstring, "----------------------------");
-
-  for(i=strlen(retstring); i<BOUNDARY_LENGTH; i++)
-    retstring[i] = table16[Curl_rand()%16];
-
-  /* 28 dashes and 12 hexadecimal digits makes 12^16 (184884258895036416)
+  /* 24 dashes and 16 hexadecimal digits makes 64 bit (18446744073709551615)
      combinations */
-  retstring[BOUNDARY_LENGTH]=0; /* zero terminate */
-
-  return retstring;
+  return aprintf("------------------------%08x%08x",
+                 Curl_rand(data), Curl_rand(data));
 }
 
 #else  /* CURL_DISABLE_HTTP */
diff --git a/lib/gtls.h b/lib/gtls.h
index 84e1396b5..453542e1e 100644
--- a/lib/gtls.h
+++ b/lib/gtls.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -55,6 +55,10 @@ void Curl_gtls_md5sum(unsigned char *tmp, /* input */
                       unsigned char *md5sum, /* output */
                       size_t md5len);
 
+/* this backend provides these functions: */
+#define have_curlssl_random 1
+#define have_curlssl_md5sum 1
+
 /* API setup for GnuTLS */
 #define curlssl_init Curl_gtls_init
 #define curlssl_cleanup Curl_gtls_cleanup
diff --git a/lib/nssg.h b/lib/nssg.h
index a881a9ad2..cd32706a7 100644
--- a/lib/nssg.h
+++ b/lib/nssg.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -60,6 +60,10 @@ void Curl_nss_md5sum(unsigned char *tmp, /* input */
                      unsigned char *md5sum, /* output */
                      size_t md5len);
 
+/* this backend provides these functions: */
+#define have_curlssl_random 1
+#define have_curlssl_md5sum 1
+
 /* API setup for NSS */
 #define curlssl_init Curl_nss_init
 #define curlssl_cleanup Curl_nss_cleanup
diff --git a/lib/sslgen.c b/lib/sslgen.c
index 48758742a..ba995cb5d 100644
--- a/lib/sslgen.c
+++ b/lib/sslgen.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -45,6 +45,16 @@
 
 #include "curl_setup.h"
 
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_STAT_H
+#include <sys/stat.h>
+#endif
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+
 #include "urldata.h"
 #define SSLGEN_C
 #include "sslgen.h" /* generic SSL protos etc */
@@ -63,6 +73,7 @@
 #include "curl_memory.h"
 #include "progress.h"
 #include "share.h"
+#include "timeval.h"
 /* The last #include file should be: */
 #include "memdebug.h"
 
@@ -159,6 +170,63 @@ void Curl_free_ssl_config(struct ssl_config_data* sslc)
   Curl_safefree(sslc->random_file);
 }
 
+
+/*
+ * Curl_rand() returns a random unsigned integer, 32bit.
+ *
+ * This non-SSL function is put here only because this file is the only one
+ * with knowledge of what the underlying SSL libraries provide in terms of
+ * randomizers.
+ *
+ * NOTE: 'data' may be passed in as NULL when coming from external API without
+ * easy handle!
+ *
+ */
+
+unsigned int Curl_rand(struct SessionHandle *data)
+{
+  unsigned int r;
+  static unsigned int randseed;
+  static bool seeded;
+
+#ifdef have_curlssl_random
+  if(!data) {
+#endif
+
+    if(!seeded) {
+
+#ifdef RANDOM_FILE
+      /* if there's a random file to read a seed from, use it */
+      int fd = open(RANDOM_FILE, O_RDONLY);
+      seeded = TRUE;
+      if(fd > -1) {
+        /* read random data into the randseed variable */
+        read(fd, &randseed, sizeof(randseed));
+        close(fd);
+      }
+      else
+#endif /* RANDOM_FILE */
+      {
+        struct timeval now = curlx_tvnow();
+        randseed += (unsigned int) now.tv_usec + (unsigned int)now.tv_sec;
+        Curl_rand(data);
+        Curl_rand(data);
+        Curl_rand(data);
+      }
+    }
+    /* Return an unsigned 32-bit pseudo-random number. */
+    r = randseed = randseed * 1103515245 + 12345;
+    return (r << 16) | ((r >> 16) & 0xFFFF);
+
+#ifdef have_curlssl_random
+  }
+  else {
+    Curl_ssl_random(data, (unsigned char *)&r, sizeof(r));
+    return r;
+  }
+#endif
+}
+
 #ifdef USE_SSL
 
 /* "global" init done? */
@@ -518,17 +586,18 @@ void Curl_ssl_free_certinfo(struct SessionHandle *data)
   }
 }
 
-#if defined(USE_SSLEAY) || defined(USE_GNUTLS) || defined(USE_NSS) || \
-    defined(USE_DARWINSSL)
-/* these functions are only used by some SSL backends */
+/* these functions are only provided by some SSL backends */
 
+#ifdef have_curlssl_random
 void Curl_ssl_random(struct SessionHandle *data,
                      unsigned char *entropy,
                      size_t length)
 {
   curlssl_random(data, entropy, length);
 }
+#endif
 
+#ifdef have_curlssl_md5sum
 void Curl_ssl_md5sum(unsigned char *tmp, /* input */
                      size_t tmplen,
                      unsigned char *md5sum, /* output */
@@ -536,6 +605,6 @@ void Curl_ssl_md5sum(unsigned char *tmp, /* input */
 {
   curlssl_md5sum(tmp, tmplen, md5sum, md5len);
 }
-#endif /* USE_SSLEAY || USE_GNUTLS || USE_NSS || USE_DARWINSSL */
+#endif
 
 #endif /* USE_SSL */
diff --git a/lib/sslgen.h b/lib/sslgen.h
index 17ad8e343..182dd8f24 100644
--- a/lib/sslgen.h
+++ b/lib/sslgen.h
@@ -33,6 +33,8 @@ bool Curl_clone_ssl_config(struct ssl_config_data* source,
                            struct ssl_config_data* dest);
 void Curl_free_ssl_config(struct ssl_config_data* sslc);
 
+unsigned int Curl_rand(struct SessionHandle *);
+
 #ifdef USE_SSL
 int Curl_ssl_init(void);
 void Curl_ssl_cleanup(void);
@@ -83,6 +85,13 @@ void Curl_ssl_md5sum(unsigned char *tmp, /* input */
 
 #define SSL_SHUTDOWN_TIMEOUT 10000 /* ms */
 
+#ifdef have_curlssl_random
+#define HAVE_CURL_SSL_RANDOM
+#endif
+#ifdef have_curlssl_md5sum
+#define HAVE_CURL_SSL_MD5SUM
+#endif
+
 #else
 /* When SSL support is not present, just define away these function calls */
 #define Curl_ssl_init() 1
diff --git a/lib/ssluse.h b/lib/ssluse.h
index bdec2b513..d6efcb271 100644
--- a/lib/ssluse.h
+++ b/lib/ssluse.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -73,6 +73,10 @@ void Curl_ossl_md5sum(unsigned char *tmp, /* input */
                       unsigned char *md5sum /* output */,
                       size_t unused);
 
+/* this backend provides these functions: */
+#define have_curlssl_random 1
+#define have_curlssl_md5sum 1
+
 /* API setup for OpenSSL */
 #define curlssl_init Curl_ossl_init
 #define curlssl_cleanup Curl_ossl_cleanup