ctypes test overwrites /dev/null

[scotdoyle]

BPO	1521375
Nosy	@theller
Files	gccdevnull.txt: Patch for Lib/ctypes/util.py util.diff: Another patch for Lib/ctypes/util.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/theller'
closed_at = <Date 2006-07-13.17:44:47.000>
created_at = <Date 2006-07-12.18:22:15.000>
labels = ['extension-modules']
title = 'ctypes test overwrites /dev/null'
updated_at = <Date 2006-07-13.17:44:47.000>
user = 'https://bugs.python.org/scotdoyle'

bugs.python.org fields:

activity = <Date 2006-07-13.17:44:47.000>
actor = 'theller'
assignee = 'theller'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2006-07-12.18:22:15.000>
creator = 'scotdoyle'
dependencies = []
files = ['2066', '2067']
hgrepos = []
issue_num = 1521375
keywords = []
message_count = 6.0
messages = ['29144', '29145', '29146', '29147', '29148', '29149']
nosy_count = 2.0
nosy_names = ['theller', 'scotdoyle']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1521375'
versions = ['Python 2.5']

[scotdoyle]

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

[theller]

Logged In: YES
user_id=11105

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"'.

[scotdoyle]

Logged In: YES
user_id=1554504

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.

[theller]

Logged In: YES
user_id=11105

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!

[scotdoyle]

Logged In: YES
user_id=1554504

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

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

[theller]

Logged In: YES
user_id=11105

Thanks. Commited as r50619.