New submission from Sebastian Rittau:
Consider the attached test case. This test will run fine with Python 2.7, but
will fail with Python 3.3. If cgi.FieldStorage() tries to parse a multipart
request without a Content-Length header in the main section, segments will have
a length of 0.
During the parse process, two instances of FieldStorage are involved. The outer
one reads the whole request and creates and delegates reading of the fragment
to inner instances.
The main problem is that FieldStorage.read_lines_to_outerboundary() of the
inner FieldStorage will read nothing, since self.limit is lower than zero.
def read_lines_to_outerboundary(self):
...
while 1:
if _read >= self.limit:
break
...
This happens, since limit is passed when creating the inner instance in
FieldStorage.read_multi():
def read_multi(self, environ, keep_blank_values, strict_parsing):
...
part = klass(self.fp, headers, ib, environ, keep_blank_values,
strict_parsing,self.limit-self.bytes_read,
self.encoding, self.errors)
...
Now, if the total request did not have a Content-Length header, self.limit will
be -1.
The naive fix works for the test case, at least, but I don't know if there are
other repercussions:
--- /usr/lib/python3.3/cgi.py 2014-02-03 22:31:16.649431125 +0100
+++ cgi.py 2014-02-03 22:32:14.849704379 +0100
@@ -788,7 +788,7 @@
last_line_lfend = True
_read = 0
while 1:
- if _read >= self.limit:
+ if self.limit >= 0 and _read >= self.limit:
break
line = self.fp.readline(1<<16) # bytes
self.bytes_read += len(line)
----------
components: Library (Lib)
files: cgi-bug.py
messages: 210166
nosy: srittau
priority: normal
severity: normal
status: open
title: cgi.FieldStorage, multipart, missing Content-Length
versions: Python 3.3
Added file: http://bugs.python.org/file33891/cgi-bug.py
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<http://bugs.python.org/issue20504>
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