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Date: Mon, 11 Mar 2024 11:30:04 -0400
From: "Skyler Ferrante (RIT Student)" <sjf5462@....edu>
To: Andreas Schwab <schwab@...e.de>
Cc: Alejandro Colomar <alx@...nel.org>, Thorsten Glaser <tg@...bsd.de>, Rich Felker <dalias@...c.org>,
musl@...ts.openwall.com, NRK <nrk@...root.org>,
Guillem Jover <guillem@...rons.org>, libc-alpha@...rceware.org,
libbsd@...ts.freedesktop.org, "Serge E. Hallyn" <serge@...lyn.com>,
Iker Pedrosa <ipedrosa@...hat.com>, Christian Brauner <christian@...uner.io>
Subject: Re: Re: Tweaking the program name for <err.h> functions
Hmm, maybe I'm missing something, but it seems you can close(fd) for
the standard fds and then call execve, and the new process image will
have no fd 0,1,2. I've tried this on a default Ubuntu 22.04 system.
This seems to affect shadow-utils and other setuid/setgid binaries.
Here is a repo I built for testing,
https://github.com/skyler-ferrante/fd_omission/. What is the correct
glibc behavior? Am I misunderstanding something?
Skyler
On Mon, Mar 11, 2024 at 11:09 AM Andreas Schwab <schwab@...e.de> wrote:
>
> On Mär 11 2024, Skyler Ferrante (RIT Student) wrote:
>
> > It seems like this is the main thing shadow-utils (and other projects)
> > should be concerned about. Every setuid/setgid program should check
> > for fd 0,1,2 being open at the start of execution, and either abort or
> > open new fds to /dev/null to prevent file descriptor omission attacks.
>
> That's what glibc already does.
>
> --
> Andreas Schwab, SUSE Labs, schwab@...e.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."
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