From: Nick Mathewson <nickm@torproject.org>
Date: Mon, 17 Sep 2012 13:52:43 +0000 (-0400)
Subject: Avoid sign-extending when computing rend auth type.
X-Git-Tag: tor-0.2.4.3-alpha~25^2
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=96d2a21683cdfe25b549e13fa450d4b12fb945b2;p=thirdparty%2Ftor.git

Avoid sign-extending when computing rend auth type.

Right-shifting negative values has implementation-defined behavior.
On all the platforms we work on right now, the behavior is to
sign-extend the input.  That isn't what we wanted in

    auth_type_val = (descriptor_cookie_tmp[16] >> 4) + 1;

Fix for 6861; bugfix on 0.2.1.5-alpha; reported pseudonymously.

The broken behavior didn't actually hurt anything, I think, since the
only way to get sign-extension to happen would be to have the top bit
of descriptor_cookie_tmp[16] set, which would make the value of
descriptor_cookie_tmp[16] >> 4 somewhere between 0b11111111 and
0b11111000 (that is, between -1 and -8).  So auth_type_val would be
between -7 and 0.  And the immediate next line does:

    if (auth_type_val < 1 || auth_type_val > 2) {

So the incorrectly computed auth_type_val would be rejected as
invalid, just as a correctly computed auth_type_val would be.

Still, this stuff shouldn't sit around the codebase.
---

diff --git a/changes/bug6861 b/changes/bug6861
new file mode 100644
index 0000000000..1040bd7a36
--- /dev/null
+++ b/changes/bug6861
@@ -0,0 +1,3 @@
+  o Minor bugfixes:
+    - Fix handling of rendezvous client authorization types over 8.
+      Fixes bug 6841; bugfix on 0.2.1.5-alpha.
diff --git a/src/or/rendclient.c b/src/or/rendclient.c
index 73e1c41d7b..2104a5b3d4 100644
--- a/src/or/rendclient.c
+++ b/src/or/rendclient.c
@@ -1250,7 +1250,7 @@ rend_parse_service_authorization(const or_options_t *options,
                descriptor_cookie);
       goto err;
     }
-    auth_type_val = (descriptor_cookie_tmp[16] >> 4) + 1;
+    auth_type_val = (((uint8_t)descriptor_cookie_tmp[16]) >> 4) + 1;
     if (auth_type_val < 1 || auth_type_val > 2) {
       log_warn(LD_CONFIG, "Authorization cookie has unknown authorization "
                           "type encoded.");