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Date: Fri, 6 Nov 2009 03:09:22 +0000
From: Joe Orton <jorton@redhat.com>
To: dev@httpd.apache.org, openssl-dev@openssl.org
Subject: Re: TLS renegotiation attack, mod_ssl and OpenSSL
Message-ID: <20091106030922.GA3764@redhat.com>
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References: <20091105140126.GA32416@redhat.com> <4AF2F19A.9010509@links.org>
 <20091105173221.GA1059@redhat.com> <4AF337BF.1080003@apache.org>
 <20091105213100.GA2171@redhat.com> <20091106000006.GA2911@redhat.com>
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User-Agent: Mutt/1.5.19 (2009-01-05)
Organization: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor,
 Berkshire, SL4 1TE, United Kingdom.
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 Matt Parson (USA), Charlie Peters (USA)

On Fri, Nov 06, 2009 at 12:00:06AM +0000, Joe Orton wrote:
> On Thu, Nov 05, 2009 at 09:31:00PM +0000, Joe Orton wrote:
> > * we can detect in mod_ssl when the client is renegotiating by using the 
> > callback installed using SSL_CTX_set_info_callback(), in conjunction 
> > with suitable flags in the SSLConnRec to detect the cases where this is 
> > either a server-initiated renegotiation or the initial handshake on the 
> > connection.
> 
> Here is a very rough first hack (for discussion/testing purposes only!):

A second hack, slightly less rough hack:

Index: ssl_private.h
===================================================================
--- ssl_private.h	(revision 832979)
+++ ssl_private.h	(working copy)
@@ -335,6 +335,20 @@
     int is_proxy;
     int disabled;
     int non_ssl_request;
+
+    /* Track the handshake/renegotiation state for the connection so
+     * that all client-initiated renegotiations can be rejected, as a
+     * partial fix for CVE-2009-3555. */
+    enum { 
+        RENEG_INIT = 0, /* Before initial handshake */
+        RENEG_REJECT, /* After initial handshake; any client-initiated
+                       * renegotiation should be rejected */
+        RENEG_ALLOW, /* A server-initated renegotiation is taking
+                      * place (as dictated by configuration) */
+        RENEG_ABORT /* Renegotiation initiated by client, abort the
+                     * connection */
+    } reneg_state;
+    
     server_rec *server;
 } SSLConnRec;
 
@@ -618,7 +632,7 @@
 int          ssl_callback_NewSessionCacheEntry(SSL *, SSL_SESSION *);
 SSL_SESSION *ssl_callback_GetSessionCacheEntry(SSL *, unsigned char *, int, int *);
 void         ssl_callback_DelSessionCacheEntry(SSL_CTX *, SSL_SESSION *);
-void         ssl_callback_LogTracingState(MODSSL_INFO_CB_ARG_TYPE, int, int);
+void         ssl_callback_Info(MODSSL_INFO_CB_ARG_TYPE, int, int);
 #ifndef OPENSSL_NO_TLSEXT
 int          ssl_callback_ServerNameIndication(SSL *, int *, modssl_ctx_t *);
 #endif
Index: ssl_engine_init.c
===================================================================
--- ssl_engine_init.c	(revision 832979)
+++ ssl_engine_init.c	(working copy)
@@ -520,10 +520,7 @@
     SSL_CTX_set_tmp_rsa_callback(ctx, ssl_callback_TmpRSA);
     SSL_CTX_set_tmp_dh_callback(ctx,  ssl_callback_TmpDH);
 
-    if (s->loglevel >= APLOG_DEBUG) {
-        /* this callback only logs if LogLevel >= info */
-        SSL_CTX_set_info_callback(ctx, ssl_callback_LogTracingState);
-    }
+    SSL_CTX_set_info_callback(ctx, ssl_callback_Info);
 }
 
 static void ssl_init_ctx_verify(server_rec *s,
Index: ssl_engine_io.c
===================================================================
--- ssl_engine_io.c	(revision 832979)
+++ ssl_engine_io.c	(working copy)
@@ -103,6 +103,7 @@
     ap_filter_t        *pInputFilter;
     ap_filter_t        *pOutputFilter;
     int                nobuffer; /* non-zero to prevent buffering */
+    SSLConnRec         *config;
 } ssl_filter_ctx_t;
 
 typedef struct {
@@ -193,7 +194,13 @@
 static int bio_filter_out_write(BIO *bio, const char *in, int inl)
 {
     bio_filter_out_ctx_t *outctx = (bio_filter_out_ctx_t *)(bio->ptr);
-
+    
+    /* Abort early if the client has initiated a renegotiation. */
+    if (outctx->filter_ctx->config->reneg_state == RENEG_ABORT) {
+        outctx->rc = APR_ECONNABORTED;
+        return -1;
+    }
+    
     /* when handshaking we'll have a small number of bytes.
      * max size SSL will pass us here is about 16k.
      * (16413 bytes to be exact)
@@ -476,6 +483,12 @@
     if (!in)
         return 0;
 
+    /* Abort early if the client has initiated a renegotiation. */
+    if (inctx->filter_ctx->config->reneg_state == RENEG_ABORT) {
+        inctx->rc = APR_ECONNABORTED;
+        return -1;
+    }
+
     /* In theory, OpenSSL should flush as necessary, but it is known
      * not to do so correctly in some cases; see PR 46952.
      *
@@ -1699,6 +1712,8 @@
 
     filter_ctx = apr_palloc(c->pool, sizeof(ssl_filter_ctx_t));
 
+    filter_ctx->config          = myConnConfig(c);
+
     filter_ctx->nobuffer        = 0;
     filter_ctx->pOutputFilter   = ap_add_output_filter(ssl_io_filter,
                                                        filter_ctx, r, c);
Index: ssl_engine_kernel.c
===================================================================
--- ssl_engine_kernel.c	(revision 832979)
+++ ssl_engine_kernel.c	(working copy)
@@ -733,6 +733,10 @@
                                        (unsigned char *)&id,
                                        sizeof(id));
 
+            /* Toggle the renegotiation state to allow the new
+             * handshake to proceed. */
+            sslconn->reneg_state = RENEG_ALLOW;
+            
             SSL_renegotiate(ssl);
             SSL_do_handshake(ssl);
 
@@ -754,6 +758,8 @@
             SSL_set_state(ssl, SSL_ST_ACCEPT);
             SSL_do_handshake(ssl);
 
+            sslconn->reneg_state = RENEG_REJECT;
+
             if (SSL_get_state(ssl) != SSL_ST_OK) {
                 ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r,
                               "Re-negotiation handshake failed: "
@@ -1814,76 +1820,55 @@
     return;
 }
 
-/*
- * This callback function is executed while OpenSSL processes the
- * SSL handshake and does SSL record layer stuff. We use it to
- * trace OpenSSL's processing in out SSL logfile.
- */
-void ssl_callback_LogTracingState(MODSSL_INFO_CB_ARG_TYPE ssl, int where, int rc)
+/* Dump debugginfo trace to the log file. */
+static void log_tracing_state(MODSSL_INFO_CB_ARG_TYPE ssl, server_rec *s,
+                              conn_rec *c, int where, int rc)
 {
-    conn_rec *c;
-    server_rec *s;
-    SSLSrvConfigRec *sc;
-
     /*
-     * find corresponding server
+     * create the various trace messages
      */
-    if (!(c = (conn_rec *)SSL_get_app_data((SSL *)ssl))) {
-        return;
+    if (where & SSL_CB_HANDSHAKE_START) {
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Handshake: start", SSL_LIBRARY_NAME);
     }
-
-    s = mySrvFromConn(c);
-    if (!(sc = mySrvConfig(s))) {
-        return;
+    else if (where & SSL_CB_HANDSHAKE_DONE) {
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Handshake: done", SSL_LIBRARY_NAME);
     }
-
-    /*
-     * create the various trace messages
-     */
-    if (s->loglevel >= APLOG_DEBUG) {
-        if (where & SSL_CB_HANDSHAKE_START) {
+    else if (where & SSL_CB_LOOP) {
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Loop: %s",
+                     SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
+    }
+    else if (where & SSL_CB_READ) {
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Read: %s",
+                     SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
+    }
+    else if (where & SSL_CB_WRITE) {
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Write: %s",
+                     SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
+    }
+    else if (where & SSL_CB_ALERT) {
+        char *str = (where & SSL_CB_READ) ? "read" : "write";
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
+                     "%s: Alert: %s:%s:%s",
+                     SSL_LIBRARY_NAME, str,
+                     SSL_alert_type_string_long(rc),
+                     SSL_alert_desc_string_long(rc));
+    }
+    else if (where & SSL_CB_EXIT) {
+        if (rc == 0) {
             ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Handshake: start", SSL_LIBRARY_NAME);
-        }
-        else if (where & SSL_CB_HANDSHAKE_DONE) {
-            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Handshake: done", SSL_LIBRARY_NAME);
-        }
-        else if (where & SSL_CB_LOOP) {
-            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Loop: %s",
+                         "%s: Exit: failed in %s",
                          SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
         }
-        else if (where & SSL_CB_READ) {
+        else if (rc < 0) {
             ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Read: %s",
+                         "%s: Exit: error in %s",
                          SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
         }
-        else if (where & SSL_CB_WRITE) {
-            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Write: %s",
-                         SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
-        }
-        else if (where & SSL_CB_ALERT) {
-            char *str = (where & SSL_CB_READ) ? "read" : "write";
-            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                         "%s: Alert: %s:%s:%s",
-                         SSL_LIBRARY_NAME, str,
-                         SSL_alert_type_string_long(rc),
-                         SSL_alert_desc_string_long(rc));
-        }
-        else if (where & SSL_CB_EXIT) {
-            if (rc == 0) {
-                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                             "%s: Exit: failed in %s",
-                             SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
-            }
-            else if (rc < 0) {
-                ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
-                             "%s: Exit: error in %s",
-                             SSL_LIBRARY_NAME, SSL_state_string_long(ssl));
-            }
-        }
     }
 
     /*
@@ -1903,6 +1888,60 @@
     }
 }
 
+/*
+ * This callback function is executed while OpenSSL processes the SSL
+ * handshake and does SSL record layer stuff.  It's used to trap
+ * client-initiated renegotiations, and for dumping everything to the
+ * log.
+ */
+void ssl_callback_Info(MODSSL_INFO_CB_ARG_TYPE ssl, int where, int rc)
+{
+    conn_rec *c;
+    server_rec *s;
+    SSLSrvConfigRec *sc;
+    SSLConnRec *scr;
+
+    /*
+     * find corresponding server
+     */
+    if (!(c = (conn_rec *)SSL_get_app_data((SSL *)ssl))) {
+        return;
+    }
+
+    scr = myConnConfig(c);
+    if (!scr) {
+        return;
+    }
+
+    /* If the reneg state is to reject renegotiations, check the SSL
+     * state machine and move to ABORT if a Client Hello is being
+     * read. */
+    if ((where & SSL_CB_ACCEPT_LOOP) && scr->reneg_state == RENEG_REJECT) {
+        int state = SSL_get_state(ssl);
+        
+        if (state == SSL3_ST_SR_CLNT_HELLO_A 
+            || state == SSL23_ST_SR_CLNT_HELLO_A) {
+            scr->reneg_state = RENEG_ABORT;
+            ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, c,
+                          "rejecting client initiated renegotiation");
+        }
+    }
+    /* If the first handshake is complete, change state to reject any
+     * subsequent client-initated renegotiation. */
+    else if (where & SSL_CB_HANDSHAKE_DONE && scr->reneg_state == RENEG_INIT) {
+        scr->reneg_state = RENEG_REJECT;
+    }
+
+    s = mySrvFromConn(c);
+    if (!(sc = mySrvConfig(s))) {
+        return;
+    }
+   
+    if (s->loglevel >= APLOG_DEBUG) {
+        log_tracing_state(ssl, s, c, where, rc);
+    }
+}
+
 #ifndef OPENSSL_NO_TLSEXT
 /*
  * This callback function is executed when OpenSSL encounters an extended