[ python-Bugs-1122301 ] marshal may crash on truncated input

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Bugs item #1122301, was opened at 2005-02-14 12:14
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Fredrik Lundh (effbot)
Assigned to: Nobody/Anonymous (nobody)
Summary: marshal may crash on truncated input

Initial Comment:
marshal doesn't behave well on truncated or otherwise 
malformed input.  here's a short demo script, from a 
recent comp.lang.python thread:

:::

the problem is that the following may or may not reach 
the "done!" statement, somewhat depending on python 
version, memory allocator, and what data you pass to 
dumps.

import marshal

data = marshal.dumps((1, 2, 3, "hello", 4, 5, 6))

for i in range(len(data), -1, -1):
    try:
        print marshal.loads(data[:i])
    except EOFError:
        print "EOFError"
    except ValueError:
        print "ValueError"

print "done!"

(try different data combinations, to see how far you get 
on your platform...)

fixing this should be relatively easy, and should result in 
a safe unmarshaller (your application will still have to 
limit the amount of data fed into load/loads, of course).

:::

(also note that marshal may raise either EOFError or 
ValueError exceptions, again somewhat depending on 
how the file is damaged.  a little consistency wouldn't 
hurt, but I'm not sure if/how this can be fixed...)


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