Fix a remotely triggerable assertion failure (CVE-2012-2250)

If we completed the handshake for the v2 link protocol but wound up
negotiating the wong protocol version, we'd become so confused about
what part of the handshake we were in that we'd promptly die with an
assertion.

This is a fix for CVE-2012-2250; it's a bugfix on 0.2.3.6-alpha.
All servers running that version or later should really upgrade.

Bug and fix from "some guy from France."  I tweaked his code slightly
to make it log the IP of the offending node, and to forward-port it to
0.2.4.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/or/channeltls.c b/src/or/channeltls.c
index 4e3c20ab7..d094d15af 100644
--- a/src/or/channeltls.c
+++ b/src/or/channeltls.c
@@ -1229,6 +1229,15 @@ channel_tls_process_versions_cell(var_cell_t *cell, channel_tls_t *chan)
            "handshake. Closing connection.");
     connection_or_close_for_error(chan->conn, 0);
     return;
+  } else if (highest_supported_version != 2 &&
+             chan->conn->base_.state == OR_CONN_STATE_OR_HANDSHAKING_V2) {
+    /* XXXX This should eventually be a log_protocol_warn */
+    log_fn(LOG_WARN, LD_OR,
+           "Negotiated link with non-2 protocol after doing a v2 TLS "
+           "handshake with %s. Closing connection.",
+           fmt_addr(&chan->conn->base_.addr));
+    connection_or_close_for_error(chan->conn, 0);
+    return;
   }
 
   chan->conn->link_proto = highest_supported_version;