CURLOPT_SSL_OPTIONS: added

Allow an appliction to set libcurl specific SSL options. The first and
only options supported right now is CURLSSLOPT_ALLOW_BEAST.

It will make libcurl to disable any work-arounds the underlying SSL
library may have to address a known security flaw in the SSL3 and TLS1.0
protocol versions.

This is a reaction to us unconditionally removing that behavior after
this security advisory:

http://curl.haxx.se/docs/adv_20120124B.html

... it did however cause a lot of programs to fail because of old
servers not liking this work-around. Now programs can opt to decrease
the security in order to interoperate with old servers better.

6 files changed, 40 insertions, 6 deletions

diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index a7688a7d0..571fe742a 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -2313,6 +2313,16 @@ this to 1 to enable it. By default all transfers are done using the
 cache. While nothing ever should get hurt by attempting to reuse SSL
 session-IDs, there seem to be broken SSL implementations in the wild that may
 require you to disable this in order for you to succeed. (Added in 7.16.0)
+.IP CURLOPT_SSL_OPTIONS
+Pass a long with a bitmask to tell libcurl about specific SSL behaviors.
+
+CURLSSLOPT_ALLOW_BEAST is the only supported bit and by setting this the user
+will tell libcurl to not attempt to use any work-arounds for a security flaw
+in the SSL3 and TLS1.0 protocols.  If this option isn't used or this bit is
+set to 0, the SSL layer libcurl uses may use a work-around for this flaw
+although it might cause interoperability problems with some (older) SSL
+implementations. WARNING: avoiding this work-around loosens the security, and
+by setting this option to 1 you ask for exactly that. (Added in 7.25.0)
 .IP CURLOPT_KRBLEVEL
 Pass a char * as parameter. Set the kerberos security level for FTP; this also
 enables kerberos awareness.  This is a string, \&'clear', \&'safe',
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index a9f8a9d6e..010ebc6fe 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -482,6 +482,7 @@ CURLOPT_SSLVERSION              7.1
 CURLOPT_SSL_CIPHER_LIST         7.9
 CURLOPT_SSL_CTX_DATA            7.10.6
 CURLOPT_SSL_CTX_FUNCTION        7.10.6
+CURLOPT_SSL_OPTIONS             7.25.0
 CURLOPT_SSL_SESSIONID_CACHE     7.16.0
 CURLOPT_SSL_VERIFYHOST          7.8.1
 CURLOPT_SSL_VERIFYPEER          7.4.2
@@ -573,6 +574,7 @@ CURLSSH_AUTH_KEYBOARD           7.16.1
 CURLSSH_AUTH_NONE               7.16.1
 CURLSSH_AUTH_PASSWORD           7.16.1
 CURLSSH_AUTH_PUBLICKEY          7.16.1
+CURLSSLOPT_ALLOW_BEAST          7.25.0
 CURLUSESSL_ALL                  7.17.0
 CURLUSESSL_CONTROL              7.17.0
 CURLUSESSL_NONE                 7.17.0
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 2a9957e9c..3c9c41d8a 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -673,6 +673,15 @@ typedef enum {
   CURLUSESSL_LAST     /* not an option, never use */
 } curl_usessl;
 
+/* Definition of bits for the CURLOPT_SSL_OPTIONS argument: */
+
+/* - ALLOW_BEAST tells libcurl to allow the BEAST SSL vulnerability in the
+   name of improving interoperability with older servers. Some SSL libraries
+   have introduced work-arounds for this flaw but those work-arounds sometimes
+   make the SSL communication fail. To regain functionality with those broken
+   servers, a user can this way allow the vulnerability back. */
+#define CURLSSLOPT_ALLOW_BEAST (1<<0)
+
 #ifndef CURL_NO_OLDIES /* define this to test if your app builds with all
                           the obsolete stuff removed! */
 
@@ -1506,6 +1515,9 @@ typedef enum {
   CINIT(TCP_KEEPIDLE, LONG, 214),
   CINIT(TCP_KEEPINTVL, LONG, 215),
 
+  /* Enable/disable specific SSL features with a bitmask, see CURLSSLOPT_* */
+  CINIT(SSL_OPTIONS, LONG, 216),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 
diff --git a/lib/ssluse.c b/lib/ssluse.c
index 014d5b56a..c3d5ec4c7 100644
--- a/lib/ssluse.c
+++ b/lib/ssluse.c
@@ -1566,7 +1566,10 @@ ossl_connect_step1(struct connectdata *conn,
 #endif
 
 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
-  ctx_options &= ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS;
+  /* unless the user explicitly ask to allow the protocol vulnerability we
+     use the work-around */
+  if(!conn->data->set.ssl_enable_beast)
+    ctx_options &= ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS;
 #endif
 
   /* disable SSLv2 in the default case (i.e. allow SSLv3 and TLSv1) */
diff --git a/lib/url.c b/lib/url.c
index c89234d74..b3040b26d 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -838,6 +838,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
 {
   char *argptr;
   CURLcode result = CURLE_OK;
+  long arg;
 #ifndef CURL_DISABLE_HTTP
   curl_off_t bigsize;
 #endif
@@ -847,12 +848,10 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     data->set.dns_cache_timeout = va_arg(param, long);
     break;
   case CURLOPT_DNS_USE_GLOBAL_CACHE:
-  {
     /* remember we want this enabled */
-    long use_cache = va_arg(param, long);
-    data->set.global_dns_cache = (0 != use_cache)?TRUE:FALSE;
-  }
-  break;
+    arg = va_arg(param, long);
+    data->set.global_dns_cache = (0 != arg)?TRUE:FALSE;
+    break;
   case CURLOPT_SSL_CIPHER_LIST:
     /* set a list of cipher we want to use in the SSL connection */
     result = setstropt(&data->set.str[STRING_SSL_CIPHER_LIST],
@@ -2189,6 +2188,12 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
      */
     data->set.use_ssl = (curl_usessl)va_arg(param, long);
     break;
+
+  case CURLOPT_SSL_OPTIONS:
+    arg = va_arg(param, long);
+    data->set.ssl_enable_beast = arg&CURLSSLOPT_ALLOW_BEAST?TRUE:FALSE;
+    break;
+
 #endif
   case CURLOPT_FTPSSLAUTH:
     /*
diff --git a/lib/urldata.h b/lib/urldata.h
index a959bc716..5725ba86b 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1508,6 +1508,8 @@ struct UserDefined {
   bool ftp_skip_ip;      /* skip the IP address the FTP server passes on to
                             us */
   bool connect_only;     /* make connection, let application use the socket */
+  bool ssl_enable_beast; /* especially allow this flaw for interoperability's
+                            sake*/
   long ssh_auth_types;   /* allowed SSH auth types */
   bool http_te_skip;     /* pass the raw body data to the user, even when
                             transfer-encoded (chunked, compressed) */