[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20181213171310.GR6830@bombadil.infradead.org>
Date: Thu, 13 Dec 2018 09:13:10 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Mickaël Salaün <mickael.salaun@....gouv.fr>
Cc: Mickaël Salaün <mic@...ikod.net>,
linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
James Morris <jmorris@...ei.org>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Matthew Garrett <mjg59@...gle.com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Shuah Khan <shuah@...nel.org>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
Yves-Alexis Perez <yves-alexis.perez@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH v1 0/5] Add support for O_MAYEXEC
On Thu, Dec 13, 2018 at 04:17:29PM +0100, Mickaël Salaün wrote:
> On 13/12/2018 04:02, Matthew Wilcox wrote:
> > On Wed, Dec 12, 2018 at 09:17:07AM +0100, Mickaël Salaün wrote:
> >> The goal of this patch series is to control script interpretation. A
> >> new O_MAYEXEC flag used by sys_open() is added to enable userland script
> >> interpreter to delegate to the kernel (and thus the system security
> >> policy) the permission to interpret scripts or other files containing
> >> what can be seen as commands.
> >
> > I don't have a problem with the concept, but we're running low on O_ bits.
> > Does this have to be done before the process gets a file descriptor,
> > or could we have a new syscall? Since we're going to be changing the
> > interpreters anyway, it doesn't seem like too much of an imposition to
> > ask them to use:
> >
> > int verify_for_exec(int fd)
> >
> > instead of adding an O_MAYEXEC.
>
> Adding a new syscall for this simple use case seems excessive. I think
We have somewhat less than 400 syscalls today. We have 20 O_ bits defined.
Obviously there's a lower practical limit on syscalls, but in principle
we could have up to 2^32 syscalls, and there are only 12 O_ bits remaining.
> that the open/openat syscall familly are the right place to do an atomic
> open and permission check, the same way the kernel does for other file
> access. Moreover, it will be easier to patch upstream interpreters
> without the burden of handling a (new) syscall that may not exist on the
> running system, whereas unknown open flags are ignored.
Ah, but that's the problem. The interpreter can see an -ENOSYS response
and handle it appropriately. If the flag is silently ignored, the
interpreter has no idea whether it can do a racy check or whether to
skip even trying to do the check.
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
