[ python-Bugs-1521375 ] ctypes test overwrites /dev/null

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Bugs item #1521375, was opened at 2006-07-12 20:22
Message generated for change (Comment added) made by theller
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Category: Extension Modules
Group: Python 2.5
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Scot Doyle (scotdoyle)
Assigned to: Thomas Heller (theller)
Summary: ctypes test overwrites /dev/null

Initial Comment:
Steps to reproduce on Debian Sarge:
1. ls -l /dev/null
2. wget
http://www.python.org/ftp/python/2.5/Python-2.5b2.tgz
3. tar xvzf Pyth*
4. cd Pyth*
5. ./configure
6. make
7. su
8. make test
9. ls -l /dev/null

/dev/null goes from being a special character device to
a normal file of length zero.

The following command can be used instead of step 8
above to delete /dev/null
./python -c 'import ctypes.test.test_find'


To recreate /dev/null:
1. su
2. rm /dev/null
3. mknod -m 666 /dev/null c 1 3
4. chown root:root /dev/null

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>Comment By: Thomas Heller (theller)
Date: 2006-07-13 19:44

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Thanks.  Commited as r50619.

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Comment By: Scot Doyle (scotdoyle)
Date: 2006-07-13 15:56

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Yes, not executing the command was one way to fix the bug :-)

Thanks for catching that. I verified the new patch to work.

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Comment By: Thomas Heller (theller)
Date: 2006-07-13 10:28

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Scot, your patch is not correct because 'cmd' is never
executed.  However, I was able to reproduce the overwriting
of /dev/null by calling 'ctypes.util.find_library' for a
shared lib that does not exist.  Attached is a new patch
'util.diff' which fixes the problem for me.  Can you please
verify that it also works for you?

Thanks for finding the bug and locating the problem!

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Comment By: Scot Doyle (scotdoyle)
Date: 2006-07-13 00:17

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Hey Thomas, that pointer is just what I needed :-)

/dev/null was being deleted by gcc. Discussion at
http://www.cs.helsinki.fi/linux/linux-kernel/2001-38/1503.html 

The attached patch fixed the problem on Debian Sarge and
Ubuntu 6.06.

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Comment By: Thomas Heller (theller)
Date: 2006-07-12 20:53

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Now, that is an 'interesting' bug.  ctypes.util.find_library
does execute shell commands that happen to have '/dev/null'
in them, but it is completely unclear to me how one can
overwrite /dev/null (even if root).  Can you see anything
that's wrong there (That code is not from me, and I'm not at
all an expert in linux programming)?

BTW, I cannot reproduce this on ubuntu with 'sudo ./python
-c "import ctypes.test.test_find"'.

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