Decide whether to use SSL flags based on runtime OpenSSL version.

We need to do this because Apple doesn't update its dev-tools headers
when it updates its libraries in a security patch.  On the bright
side, this might get us out of shipping a statically linked OpenSSL on
OSX.

May fix bug 1225.

[backported]

ChangeLog

@@ -8,6 +8,12 @@ Changes in version 0.2.1.23 - 2010-0?-??
       automatically discard guards picked using the old algorithm. Fixes
       bug 1217; bugfix on 0.2.1.3-alpha. Found by Mike Perry.
 
+  o Minor bugfixes:
+    - When deciding whether to use strange flags to turn TLS renegotiation
+      on, detect the OpenSSL version at run-time, not compile time.  We
+      need to do this because Apple doesn't update its dev-tools headers
+      when it updates its libraries in a security patch.
+
   o Minor features:
     - Avoid a mad rush at the beginning of each month when each client
       rotates half of its guards. Instead we spread the rotation out

src/common/tortls.c

@@ -53,6 +53,24 @@
 
 #define ADDR(tls) (((tls) && (tls)->address) ? tls->address : "peer")
 
+/* We redefine these so that we can run correctly even if the vendor gives us
+ * a version of OpenSSL that does not match its header files.  (Apple: I am
+ * looking at you.)
+ */
+#ifndef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
+#define SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION 0x00040000L
+#endif
+#ifndef SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
+#define SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION 0x0010
+#endif
+
+/** Does the run-time openssl version look like we need
+ * SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION? */
+static int use_unsafe_renegotiation_op = 0;
+/** Does the run-time openssl version look like we need
+ * SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION? */
+static int use_unsafe_renegotiation_flag = 0;
+
 /** Structure holding the TLS state for a single connection. */
 typedef struct tor_tls_context_t {
   int refcnt;
@@ -309,9 +327,29 @@ static void
 tor_tls_init(void)
 {
   if (!tls_library_is_initialized) {
+    long version;
     SSL_library_init();
     SSL_load_error_strings();
     crypto_global_init(-1);
+
+    version = SSLeay();
+    if (version >= 0x009070c0L && version < 0x00908000L) {
+      log_notice(LD_GENERAL, "OpenSSL %s looks like version 0.9.7l or later; "
+                 "I will try SSL3_FLAGS and SSL3_OP to enable renegotation",
+                 SSLeay_version(SSLEAY_VERSION));
+      use_unsafe_renegotiation_flag = 1;
+      use_unsafe_renegotiation_op = 1;
+    } else if (version >= 0x009080c0L) {
+      log_notice(LD_GENERAL, "OpenSSL %s looks like version 0.9.8l or later; "
+                 "I will try SSL3_FLAGS and SSL_OP to enable renegotiation",
+                 SSLeay_version(SSLEAY_VERSION));
+      use_unsafe_renegotiation_flag = 1;
+      use_unsafe_renegotiation_op = 1;
+    } else {
+      log_info(LD_GENERAL, "OpenSSL %s has version %lx",
+               SSLeay_version(SSLEAY_VERSION), version);
+    }
+
     tls_library_is_initialized = 1;
   }
 }
@@ -568,7 +606,6 @@ tor_tls_context_new(crypto_pk_env_t *identity, unsigned int key_lifetime)
   SSL_CTX_set_options(result->ctx,
                       SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION);
 #endif
-#ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
   /* Yes, we know what we are doing here.  No, we do not treat a renegotiation
    * as authenticating any earlier-received data.
    *
@@ -577,9 +614,10 @@ tor_tls_context_new(crypto_pk_env_t *identity, unsigned int key_lifetime)
    * seems) broke anything that used SSL3_FLAGS_* for the purpose.  So we need
    * to do both.)
    */
-  SSL_CTX_set_options(result->ctx,
-                      SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION);
-#endif
+  if (use_unsafe_renegotiation_op) {
+    SSL_CTX_set_options(result->ctx,
+                        SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION);
+  }
   /* Don't actually allow compression; it uses ram and time, but the data
    * we transmit is all encrypted anyway. */
   if (result->ctx->comp_methods)
@@ -920,19 +958,16 @@ tor_tls_set_renegotiate_callback(tor_tls_t *tls,
 }
 
 /** If this version of openssl requires it, turn on renegotiation on
- * <b>tls</b>.  (Our protocol never requires this for security, but it's nice
- * to use belt-and-suspenders here.)
+ * <b>tls</b>.
  */
 static void
 tor_tls_unblock_renegotiation(tor_tls_t *tls)
 {
-#ifdef SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
   /* Yes, we know what we are doing here.  No, we do not treat a renegotiation
    * as authenticating any earlier-received data. */
-  tls->ssl->s3->flags |= SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;
-#else
-  (void)tls;
-#endif
+  if (use_unsafe_renegotiation_flag) {
+    tls->ssl->s3->flags |= SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;
+  }
 }
 
 /** If this version of openssl supports it, turn off renegotiation on
@@ -942,11 +977,7 @@ tor_tls_unblock_renegotiation(tor_tls_t *tls)
 void
 tor_tls_block_renegotiation(tor_tls_t *tls)
 {
-#ifdef SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
   tls->ssl->s3->flags &= ~SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;
-#else
-  (void)tls;
-#endif
 }
 
 /** Return whether this tls initiated the connect (client) or