[New-bugs-announce] [issue3144] popen / popen[234] inconsistent fd behavior

Justin Cappos report at bugs.python.org
Thu Jun 19 21:18:29 CEST 2008

New submission from Justin Cappos <justincappos at hotmail.com>:

The behavior of popen vs popen[2-4] differs with respect to open file
descriptors (at least on the Linux implementation of popen).   popen
does not close file descriptors, thus processes retain open file
descriptors from their parent.   This is likely not desirable for
security and stability reasons.   

If this isn't fixed, at a minimum it would be a good thing to document.

Here is an example that demonstrates the issue:

<<< start of open_and_popen.py>>>
# This will not be printed if popen closes file descriptors

import os
myfd = os.open("open_and_popen.py",os.O_RDONLY)

readfo = os.popen("python print_from_fd.py "+str(myfd),"r")

print "os.popen results in:"
print readfo.read()
# it will print the first line of the file here

(junkinfo, readfo) = os.popen2("python print_from_fd.py "+str(myfd),"r")

print "os.popen2 results in:"
print readfo.read()
# the child got an error, so this is just the error text

<<< end of open_and_popen.py>>>

<<< start of print_from_fd.py>>>
import os
import sys
print os.read(int(sys.argv[1]),60)
<<< end of print_from_fd.py>>>

components: Library (Lib)
messages: 68416
nosy: justincappos
severity: normal
status: open
title: popen / popen[234] inconsistent fd behavior
type: security

Python tracker <report at bugs.python.org>

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