Question

How can you create a temporary FIFO (named pipe) in Python? This should work:

import tempfile

temp_file_name = mktemp()
os.mkfifo(temp_file_name)
open(temp_file_name, os.O_WRONLY)
# ... some process, somewhere, will read it ...

However, I’m hesitant because of the big warning in Python Docs 11.6 and potential removal because it’s deprecated.

EDIT: It’s noteworthy that I’ve tried tempfile.NamedTemporaryFile (and by extension tempfile.mkstemp), but os.mkfifo throws:

OSError -17: File already exists

when you run it on the files that mkstemp/NamedTemporaryFile have created.

Answer 1

os.mkfifo() will fail with exception OSError: [Errno 17] File exists if the file already exists, so there is no security issue here. The security issue with using tempfile.mktemp() is the race condition where it is possible for an attacker to create a file with the same name before you open it yourself, but since os.mkfifo() fails if the file already exists this is not a problem.

However, since mktemp() is deprecated you shouldn’t use it. You can use tempfile.mkdtemp() instead:

import os, tempfile

tmpdir = tempfile.mkdtemp()
filename = os.path.join(tmpdir, 'myfifo')
print filename
try:
    os.mkfifo(filename)
except OSError, e:
    print "Failed to create FIFO: %s" % e
else:
    fifo = open(filename, 'w')
    # write stuff to fifo
    print >> fifo, "hello"
    fifo.close()
    os.remove(filename)
    os.rmdir(tmpdir)

EDIT: I should make it clear that, just because the mktemp() vulnerability is averted by this, there are still the other usual security issues that need to be considered; e.g. an attacker could create the fifo (if they had suitable permissions) before your program did which could cause your program to crash if errors/exceptions are not properly handled.