From patchwork Thu Jan 31 19:01:40 2013
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Subject: tests: fix toctou race in tinyproxy.py (issue3795)
From: Mads Kiilerich <mads@kiilerich.com>
X-Patchwork-Id: 775
Message-Id: <9f4ee36491d826a07141.1359658900@mk-desktop>
To: mercurial-devel@selenic.com
Date: Thu, 31 Jan 2013 20:01:40 +0100

# HG changeset patch
# User Mads Kiilerich <madski@unity3d.com>
# Date 1359655993 -3600
# Branch stable
# Node ID 9f4ee36491d826a0714164721e631f026d63b324
# Parent  2a1fac3650a5b4d650198604c82ab59969500374
tests: fix toctou race in tinyproxy.py (issue3795)

test-http-proxy.t sometimes failed with:
    File ".../tests/tinyproxy.py", line 110, in _read_write
      data = i.recv(8192)
  error: (104, 'Connection reset by peer')

This might have started showing up with a9fd11ffa13f ... but it has apparently
also been seen before. I don't see anything in a9fd11ffa13f that can explain
it. It seems to be a race in test, in the tinyproxy helper:

Tinyproxy found an incoming socket using select(). It would break the loop if
an error had been detected on the socket, but there was no error and it tried
to recv() from the socket. That failed - apparently because it had been reset
after select().

Errors in the recv() will now be caught and will break the loop like errors
detected by select() would.

(send() could also fail in a similar way ... but using the same solution there
and losing data we have read doesn't feel right.)

diff --git a/tests/tinyproxy.py b/tests/tinyproxy.py
--- a/tests/tinyproxy.py
+++ b/tests/tinyproxy.py
@@ -107,7 +107,10 @@
                         out = self.connection
                     else:
                         out = soc
-                    data = i.recv(8192)
+                    try:
+                        data = i.recv(8192)
+                    except socket.error:
+                        break
                     if data:
                         out.send(data)
                         count = 0