[Python-Dev] PEP 446: Open issues/questions

[Antoine Pitrou]

Le Sun, 28 Jul 2013 12:18:55 +0200,
Charles-François Natali <cf.natali at gmail.com> a écrit :
> 2013/7/28 Antoine Pitrou <solipsis at pitrou.net>:
> >> (C) Should we handle standard streams (0: stdin, 1: stdout, 2:
> >> stderr) differently? For example, os.dup2(fd, 0) should make the
> >> file descriptor 0 (stdin) inheritable or non-inheritable? On
> >> Windows, os.set_inheritable(fd, False) fails (error 87, invalid
> >> argument) on standard streams (0, 1, 2) and copies of the standard
> >> streams (created by os.dup()).
> >
> > I have been advocating for that, but I now realize that
> > special-casing these three descriptors in a myriad of fd-creating
> > functions isn't very attractive.
> > (if a standard stream fd has been closed, any fd-creating function
> > can re-create that fd: including socket.socket(), etc.)
> >
> > So perhaps only the *original* standard streams should be left
> > inheritable?
> 
> Having stdin/stdout/stderr cloexec (e.g. after a dup() to redirect to
> a log file, a socket...) will likely break a lot of code, e.g. code
> using os.system(), or code calling exec manually (and I'm sure there's
> a bunch of it).

Hmm. os.exec*() could easily make standard streams non-CLOEXEC before
calling the underlying C library function. Things are more annoying for
os.system(), though.

> Also, it'll be puzzling to have syscalls automatically set the cloexec
> flag. I guess a lot of people doing system programming with Python
> will get bitten, but that's a discussion we already had months ago...

Perhaps this advocates for a global flag, e.g.
sys.set_default_fd_inheritance(), with False (non-inheritable) being
the default for sanity and security.

Regards

Antoine.