[ python-Bugs-1177468 ] random.py/os.urandom robustness

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Bugs item #1177468, was opened at 2005-04-05 18:03
Message generated for change (Comment added) made by majid
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Fazal Majid (majid)
Assigned to: Nobody/Anonymous (nobody)
Summary: random.py/os.urandom robustness

Initial Comment:
Python 2.4.1 now uses os.urandom() to seed the random
number generator. This is mostly an improvement, but
can lead to subtle regression bugs.

os.urandom() will open /dev/urandom on demand, e.g.
when random.Random.seed() is called, and keep it alive
as os._urandomfd.

It is standard programming practice for a daemon
process to close file descriptors it has inherited from
its parent process, and if it closes the file
descriptor corresponding to os._urandomfd, the os
module is blissfully unaware and the next time
os.urandom() is called, it will try to read from a
closed file descriptor (or worse, a new one opened
since), with unpredictable results.

My recommendation would be to make os.urandom() open
/dev/urandom each time and not keep a persistent file
descripto. This will be slightly slower, but more
robust. I am not sure how I feel about a standard
library function steal a file descriptor slot forever,
specially when os.urandom() is probably going to be
called only once in the lifetime of a program, when the
random module is seeded.


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>Comment By: Fazal Majid (majid)
Date: 2005-04-05 18:06

Message:
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There are many modules that have a dependency on random, for
instance os.tempnam(), and a program could well
inadvertently use it before closing file descriptors.

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